A piston is the part that moves up and down inside the engine cylinder. When fuel burns, it pushes the piston, and that motion turns the crankshaft to make power.
An engine rebuild is when you take the engine apart and replace worn parts so it runs like it should again. People do it when mileage or wear makes the engine less reliable.
A “bottom end” build focuses on the lower rotating assembly (crankshaft, connecting rods, and pistons) to increase strength for higher power. The episode frames a common misconception: that you must always build the bottom end when you turn up diesel power, when the right piston choice and application matter more.
The piston has a little “cup” on top where combustion happens. That cup shape matters because it helps the fuel burn the right way, which affects power and how smooth the engine runs.
“24 valve” means the engine has more valves than a 12-valve setup. More valves can help the engine breathe and run differently, so piston and combustion parts may need to match that design.
With direct injection, the fuel is sprayed right into the engine’s burning area. That helps the engine control the burn more accurately, which can improve power and fuel economy.
Duramax is GM’s diesel engine line. The host is saying GM changed the shape of the combustion area in the piston over the years so the engine burns fuel more cleanly and efficiently.
Powerstroke is Ford’s diesel engine family. The point here is that Ford’s diesel combustion design has been updated over time to meet emissions and improve how the fuel burns.
Cummins builds diesel engines, especially for trucks. The host is saying their diesel combustion design has evolved over the years to meet changing emissions rules.
Mercedes is mentioned as another diesel manufacturer that changed combustion design over time. The underlying idea is that bowl/head geometry and injection strategy evolve across brands as emissions regulations tighten.
TDI is Volkswagen’s diesel technology branding. In this segment, it’s used to illustrate that even within the same general diesel concept, manufacturers altered combustion-chamber/bowl design as injection systems and emissions requirements changed.
Concept
combustion chamber location (piston vs head)
The episode contrasts diesel designs where the combustion chamber is largely in the piston (with a flat cylinder head) versus designs where the chamber is in the head. This “flip-flop” affects airflow, valve placement, and how engineers package the engine for performance and emissions.
Concept
bigger valves because of angled valve placement
The host claims that with the diesel’s combustion-chamber packaging (piston-based chamber and flat head), valve angles allow larger valves and more effective flow area. In general, valve size and angle influence how well the engine breathes, which can improve combustion efficiency and power potential.
Diesel engines don’t breathe and burn fuel the same way as gas engines. Because of that, they can get away with smaller valves since the fuel-injection and in-cylinder mixing do a lot of the work. It’s a design tradeoff, not a simple “bigger is better” rule.
In many diesel engines, the piston crown includes a bowl-shaped cavity that helps capture the injected fuel and promote mixing with air. Bowl geometry (depth, width, and shape) strongly influences swirl, fuel distribution, and combustion quality, which is why different “bowl styles” exist for different engine targets like emissions and efficiency.
The fuel injector is what sprays diesel fuel into the cylinder. Because diesel doesn’t use a spark like gasoline, the injector’s spray pattern and timing are crucial for getting the fuel to mix with air and burn properly. That’s why injector behavior and piston bowl shape are linked.
The intake charge is what the engine pulls into the cylinder during the intake stroke. In gasoline engines it’s often a more ready-to-burn mixture, while diesels bring in mostly air and then add fuel later by injection. That’s why the “mixing job” is different between gas and diesel.
Diesel needs good mixing inside the cylinder. The fuel has to break up and spread out so it can mix with air and burn efficiently. Bowl shape and spray direction help create that swirling motion.
Mixing action is how well the fuel and air get blended together. If they mix well, the diesel burns more completely, which usually means less smoke and better response.
Swirl is the spinning motion of air inside the cylinder. “Swirl numbers” are a way to describe how much that spinning happens, and more swirl usually helps the fuel mix better so you get less smoke and better drivability.
Throttle response is how quickly the truck feels like it reacts when you press the pedal. If the fuel-air mixing is better, the engine tends to respond more cleanly and quickly.
Term
PM
PM is basically soot/smoke particles from incomplete burning. When the engine mixes fuel and air better, it tends to make less PM.
Injector open time is how long the diesel nozzle sprays fuel. If it sprays for a shorter time, you may get less “help” from the spray to mix the fuel, so the cylinder’s swirl and piston shape matter more.
EcoBoost is Ford’s name for a turbo gas engine. It’s designed to make good power while using less fuel, and it can use direct injection—meaning fuel is sprayed directly into the cylinder.
A “diesel bowl” refers to the piston crown bowl/combustion chamber geometry used in many diesel engines to shape airflow and fuel spray for reliable ignition. The host is contrasting diesel piston bowl design with newer gasoline engines that are adding similar piston bowl features due to direct injection and boosting.
Term
common road
This is referring to “Common Rail,” a modern diesel fuel system. Instead of each injector making its own pressure, a shared high-pressure line feeds the injectors so the engine can inject fuel more precisely.
Term
non re-entrant vs entrant
This is about the shape of the combustion chamber. Different shapes change how air moves and how the fuel mixes, which can affect how smoothly the diesel runs and how clean it burns.
On a diesel piston, the top has a “bowl” where fuel sprays and burns. A re-entrant bowl is shaped like it dips in and then comes back out, which helps the fuel and air mix better so it burns more cleanly.
QSP here refers to a wide-bowl piston meant more for off-road work. The wider bowl changes how the fuel and air swirl together, which can help under tough conditions even if it’s not as focused on street cleanliness.
ISB here means a narrow-bowl piston meant for highway/road use. The bowl shape helps the diesel fuel mix with air in a way that usually makes the engine burn cleaner during normal driving.
In a diesel, the piston bowl helps create a swirling motion of air. That swirl direction and strength determine how well the fuel mixes, which can change how cleanly the engine burns.
Common-rail is a modern diesel fuel system where fuel pressure is stored in a shared “rail” and injected electronically. Because injection is more precise, the piston bowl shape and airflow swirl matter a lot for how cleanly the diesel burns.
Nitrous oxide is a chemical you can inject into the engine to make it produce extra power. It’s like a temporary boost because it helps the engine burn more fuel. Because it makes the engine work harder, the engine parts need to handle the extra stress.
Term
white bowl
“White bowl” sounds like a nickname for a particular piston top shape used in diesel builds. Different bowl shapes can change how the engine burns fuel. The host is saying some people swear by that design, but their results may depend on how they set up fueling.
Top dead center is the moment when the piston is at the very top of its travel. When diesel fuel is injected before or after that point, it changes how smoothly the engine burns. In this segment, they’re saying some piston bowl shapes work best with fuel injected right around that top position.
Concept
injection timing vs piston bowl geometry
It’s not just the piston shape or just the fuel timing—both have to work together. The piston bowl helps control how the fuel mixes and burns, and the timing of when fuel is injected changes that mixing. If they don’t match, the engine can run dirtier or make less power.
A split injection means the engine sprays fuel in two stages instead of all at once. For example, “80/20” means most of the fuel is injected before the piston reaches its highest point, and the rest is injected after. That helps the engine burn fuel more smoothly and can reduce smoke.
The Toyota Supra is a sports car built for speed and driving fun. People talk about it a lot because it’s popular with car enthusiasts who like to modify and tune cars. When it’s mentioned alongside “split” ideas, it usually means different ways of setting up how power or traction is handled.
The “bowl” is the shaped recess in the piston crown that helps direct airflow and fuel spray for diesel combustion. A “wide bowl” changes how the injected fuel mixes as the piston moves, which can affect smoke/haze and combustion stability. The segment suggests that when you use split injection with a wide bowl, you may see more visible haze under high power.
BSFC is basically a “miles-per-gallon” style number, but for engines: it tells you how much fuel you burn to make a certain amount of power. Lower BSFC means better efficiency. The hosts are saying factories might pick piston and combustion designs to hit better BSFC numbers for certain equipment.
Concept
piston bowl design tradeoffs for RPM range and emissions
Diesel piston bowl design is a balancing act between combustion efficiency, performance, and emissions compliance. Bowl shape can favor either a narrow RPM band (better transient behavior) or steady RPM operation (better long-duration efficiency), while emissions requirements constrain the final design.
A “narrow bowl” means the diesel’s top-pocket is smaller and more focused. That can help the engine burn fuel more consistently when you’re not just holding one steady RPM.
Diesel efficiency depends a lot on where the engine is operating (RPM and how hard it’s working). Generators usually run at one steady speed, so the piston design can be chosen to be best at that condition.
“Robust piston” here refers to piston strength and thermal tolerance—how well it resists cracking or melting under heat and cylinder pressure. The speaker claims narrow-bowl pistons are more abuse-tolerant, which matters in higher-load diesel builds.
The “eighth mile” is a drag strip measurement that’s shorter than the quarter mile. It’s commonly used to see how well a build launches and accelerates.
Concept
bottom end (engine strength)
“Bottom end” is the engine’s lower parts that take the hardest loads—like the crank and rods. When diesel guys mention it, they mean making sure those parts can handle the extra force from high power.
Diesel engines inject fuel at a specific moment in the engine cycle. If you inject it earlier or later, the engine burns the fuel differently, which can affect power, smoke, and emissions.
In a diesel, the combustion chamber has a “bowl” shape that helps the fuel spray mix with air. A wide bowl gives more space for the fuel to spread and burn, especially when you’re injecting in multiple stages.
The shape of the combustion chamber changes how the fuel spray behaves. Because of that, tuning (fuel timing and injection amounts) often has to be adjusted depending on whether the engine uses a wide or narrow bowl.
As emissions rules get stricter, manufacturers often change how the engine burns fuel and how it injects fuel. That can mean different injector and combustion-chamber designs to keep exhaust cleaner.
Instead of spraying all the fuel at once, some diesel setups inject it in stages. That helps the engine burn cleaner and can reduce noise and exhaust smoke.
Diesel engines can inject fuel in more than one burst. The “pilot” and “post” are smaller injections around the main injection to help the burn happen the way the calibration wants.
A timing map is basically the computer’s “schedule” for when the engine’s combustion happens. It changes depending on how hard you’re driving and how fast the engine is spinning, so the engine burns fuel efficiently.
Instead of using extra exhaust gadgets to clean the smoke, the engine can be tuned to burn fuel more cleanly inside the cylinder. That usually involves changing how and when fuel is injected and how the piston’s combustion chamber is shaped.
This is a piston shape choice. The “bowl” on top of the piston changes how the fuel-air mixture burns, and the hosts prefer the narrow version for everyday performance builds because it tends to work better in practice.
This is the same idea as the narrow ball piston, but with a wider shape on top. The hosts say it can help make a little more power for some setups, but it may not be the best choice if you care most about longevity and clean operation.
Concept
diesel piston efficiency vs fuel mileage
They’re warning you not to assume that if a piston is “a little more efficient,” your fuel economy will improve by the same percentage. Real fuel mileage depends on how you drive and how the whole engine system is set up, not just the piston.
A 90/10 split is another two-shot injection strategy where almost all the fuel goes in before the piston reaches the top. The idea is that the piston’s bowl shape can handle that better.
The Ford F-150 is a large pickup truck used for hauling, towing, and general driving. Some owners upgrade engine parts to make more power, including pistons. The podcast is basically asking whether certain upgrades are necessary or smart for a specific truck and model year.
Compression height is a measurement that affects where the piston sits in the engine. Changing it can change clearances and compression, so it’s important when you’re building a custom piston.
Cast pistons are the more common, mass-produced type of piston. They’re usually cheaper than forged pistons, but the host is explaining that diesel engines can be harder on piston/ring areas.
The ring land is where the piston rings sit. Using a steel ring land helps the top ring survive longer because it’s more resistant to wear, which matters a lot in diesel engines.
Soot is the black, dusty stuff that can come out of the exhaust when fuel doesn’t burn completely. In diesel engines, soot can be harsh on internal parts, so builders think about piston and ring wear.
Anodized coatings are a protective surface layer that makes parts harder and more wear-resistant. The host is saying this helps forged pistons last longer in diesel-style conditions.
Piston rings need a little space to move correctly. If they’re too tight, soot can build up and stop them from working; if they’re designed with the right clearance, they can keep cleaning themselves.
A factory piston is the stock piston that came with the engine from the factory. It’s designed for normal driving and normal power. If you push the engine harder, it may not last as long as a stronger aftermarket piston.
A keystone ring is a piston ring shaped like a wedge. That shape helps it seal better and can help control oil by scraping it more effectively. The idea is that the ring design can improve how the engine manages oil and compression.
A rectangle ring is the more traditional piston ring shape—basically a rectangular profile. It doesn’t have the wedge/keystone geometry that can change how the ring seals and controls oil. The hosts bring it up mainly to compare designs.
The oil ring helps control how much engine oil gets wiped onto the cylinder walls. If it doesn’t work well, you can burn more oil or get more buildup. The hosts are saying the diesel-focused ring sets they like use a different oil-ring design for better control.
Pistons have rings that help control oil inside the engine. The oil control ring is the one that keeps extra oil from getting into the combustion area. If it doesn’t do its job well, the engine can burn more oil.
A hyper-eutectic piston is a special cast piston made with extra silicon. That silicon helps the piston stay more stable as the engine heats up and cools down. So it tends to change size less than other piston materials.
Piston wall clearance is the designed gap between the piston and the cylinder wall when cold. Builders set it based on expected operating temperatures and piston expansion so the piston doesn’t seize or scuff when hot. The segment describes using “very, very large” clearances for race engines to prevent contact under extreme conditions.
“Scuffed” refers to damage where the piston surface or skirt rubs against the cylinder wall, leaving marks and potentially accelerating wear. In performance builds, scuffing often points to incorrect clearances, poor piston fit, or insufficient lubrication under heat/load. The hosts connect scuffing risk to piston clearance choices.
Concept
cast vs forged piston tradeoffs
The segment is essentially comparing cast vs forged piston tradeoffs for diesel street trucks: cast pistons may be noisier, burn more oil, and wear bores faster due to more piston movement, but they can include complex OEM oil-cooling passages. Forged pistons are described as more rigid and better for high-RPM durability, but they may lack certain internal cooling grooves that require casting. This is a practical concept for choosing piston strategy based on intended use and cooling design.
Forged pistons are made by compressing and shaping metal, which usually makes them tougher and more rigid. Because they fit more tightly, they can reduce the piston’s side-to-side movement in the cylinder. That can mean less noise and less oil burning, but they may not include the same built-in oil-cooling shapes as some factory cast pistons.
Piston rocking means the piston isn’t perfectly steady in the cylinder—it shifts slightly as the engine loads change. When that happens, it can scrape or stress the cylinder walls more and can also disturb the oil control rings. Over time, that can wear the engine faster and may increase oil burning.
Bore wear is when the inside cylinder wall slowly gets worn down. The piston and rings rub against it every time the engine runs. If the piston isn’t stable, that rubbing gets worse, so the cylinder wears out faster.
An oil cooling galley is a built-in oil channel inside the piston that sends oil where it’s needed for cooling. The idea is to keep the piston from getting too hot during heavy driving. Cooler pistons are less likely to fail from heat stress.
A “J jet” is basically an oil sprayer/nozzle in the engine. It shoots oil onto the piston to help cool it down. More effective cooling helps the engine handle heavy load without overheating.
This is how hot the engine gets when you’re driving hard or towing. The segment is saying that better oil cooling helps keep piston temperatures under control. That reduces the chance of heat damage.
Car
Cummins 5.9 common rail
The 5.9L Cummins common-rail diesel is a popular diesel engine setup. They’re saying that for this engine you can choose different piston materials, including steel.
Car
Ford Power Stroke
Power Stroke is Ford’s diesel engine. They’re saying newer versions came with steel pistons, and older trucks can be upgraded to that style.
Piston-to-wall clearance is the small gap between the piston and the cylinder. Too much gap can reduce performance and increase wear; too little can cause rubbing when everything heats up.
A steel piston is made from steel instead of the more common aluminum. It can be chosen for durability in certain heavy-duty uses. In a build, the key is making sure the piston’s expansion matches the engine’s cylinder/block so it doesn’t rub when hot.
This is the little gap between the piston and the cylinder wall. When the engine heats up, the piston grows, so you need enough space to prevent rubbing. The “right” gap depends on the piston material and how it expands compared to the engine block.
Concept
piston material expansion vs block material
Different materials expand at different rates when they heat up. If the piston and the engine block expand similarly, you can run a tighter gap safely. If they don’t match, the piston can grow into the cylinder wall and cause damage.
The Tesla Semi is an electric truck built to move freight over long distances. Because it’s electric, it doesn’t use a traditional engine with pistons like many diesel trucks do. That’s why the conversation compares “semi truck applications” to what’s actually used in an electric design.
Concept
semi truck vs passenger-car diesel build parts sourcing
Some parts are common in heavy-duty trucks but harder to find for other diesel builds. If you can’t easily source the right pistons, it can limit what power level or setup you can safely run. Builders often rely on what’s proven and available for their engine type.
VP44 is a specific diesel fuel injection pump design used on some engines. Changing to or from a VP44 setup can change how much fuel the engine can deliver and how hard the internals have to work. That’s why it comes up when planning what power level to build for.
Low compression means the engine squeezes the air/fuel mixture less than usual. That usually makes the engine run with less stress inside the cylinder. Builders use it when they want the engine to handle more abuse or different fuel/tuning.
Valve relief pistons have small notches on the top of the piston. Those notches give extra space so the valves don’t hit the piston. It’s a safety/fitment thing, especially after engine modifications.
“12 valves” is how many valves the engine has in total. More valves usually means more ways to breathe, but the key point is that this specific head design changes how the fuel burns. That’s why piston shape and compression matter a lot.
Non-intercooled means the turbocharged air goes straight into the engine without being cooled first. Hot intake air can make the engine run harder and can increase smoke/heat. So builders often adjust piston/compression to match that setup.
Injectors are the parts that spray diesel fuel into the engine. If they’re the right ones and the computer is tuned correctly, the fuel burns cleaner and you can make more power.
“Deckplating” means machining the engine block’s deck surface to change piston-to-head clearance and effectively alter compression and combustion geometry. In high-power diesel builds, it’s used to fine-tune compression ratio and help manage cylinder pressure when running extreme fueling.
They’re describing a situation where the engine is forced to behave like it has higher compression than you’d normally get. That can make huge power, but it also makes the engine harder on parts like pistons and the block.
Horsepower is basically how much “pull” the engine can make. A big number on paper doesn’t always mean the truck will feel good to drive—how it makes power and how cleanly it burns matters.
On a diesel, smoke usually means the fuel isn’t burning as completely as it should. A build that’s “smoky” may feel strong, but it can be inefficient and unpleasant (and sometimes harder on components) compared to a cleaner, more balanced setup.
Compression is how tightly the engine squeezes the fuel/air before it lights. More compression can make more power, but you have to tune everything else so it burns correctly and doesn’t cause problems.
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Hello, everybody. Welcome back to the Power Juven podcast.
Today we're going to talk about pistons, fat pistons, white pistons,
If you have a question about pistons, we're here for you.
Now, a lot of people, their trucks are getting higher mileage
and they need to refresh or rebuild their engine.
So we get a lot of questions.
What piston is best for my application or my purpose?
The other reason this topic comes up is outside of the diesel performance world.
When you build an engine and you build the bottom end, you get in there
and you put these aftermarket forged erase pistons in there and, you know,
to hold the power.
And so a lot of guys are if they're coming from the other performance world,
in the diesel, they think they need to build the bottom end
because they're going to turn up the power.
So we're going to answer all those questions today.
Yeah. And so where do you start?
Like, I mean, I think we should start with a fact of like piston bull design.
There's lots of different designs.
You can get, you know, 12 valve, 24 valve, you know, common rail stuff.
They have different designs.
Why do they offer different designs and what's the benefits of each?
On a diesel, they're direct injected.
And so the air comes in the chamber.
It's in there and you inject the fuel into it.
The combustion chamber on a diesel is the piston bull.
That's where that fuel and air mixture action happens.
And so there's a bunch of different bull designs
because depending on the injection system, the pressure comes in.
The time that it was made was this designed in the 80s,
was designed in emission era.
They've changed the design of the bull quite a bit on Cummins,
Powerstroke, Duramax, all of them.
Mercedes, TDI, Volkswagen, all of them have changed over the years,
depending on what's happened.
But the reason that it's there is because that's where the fuel and the air
mix and that's what controls the burn characteristics of the engine.
And this seems like super common sense to us.
Like we don't even think about it like to me, the opposite would be weird.
But I still run into people that don't realize that a Cummins head
and most diesel heads are completely flat.
There's no chamber in the head.
It's all in the piston.
So they flip flopped it.
And that is a benefit in the gas rule in that you can put bigger valves
because the valves come in at an angle you have more surface area to work with.
And that is a big limitation the diesel has,
is that's why diesels have much smaller valves for a given cubic inch
because they don't have the surface area to work with
because they're not coming at an angle they're restricted to the flat level.
And so our valves are quite small compared to a gasoline of this similar.
And you think about it, but yeah, gas head, they have a chamber
and tons of chamber designs, what the application is, emission standards,
whatever the chamber of a diesel is in the piston in the bowl.
And they do that.
I mean, I'm sure there's many reasons, but at least partially
because the diesel engine throws fuel from from the injector
and it shoots it downwards into the chamber
and you need a nice deep chamber to grab that fuel.
Gas obviously comes in with the intake charge.
They don't really care where that chamber is and how it works necessarily
as long as it's there and it's designed within whatever criteria they're looking for.
And so because we're shooting fuel into the cylinder while that pistons coming up,
we need a nice deep chamber for that fuel to go in, swirl around, mix up and burn in.
And that's that's why and that's also a lot of the reasons
why there's different styles of pistons and different bowls, wide bowls, narrow bowls,
different profiles there because you're changing kind of how the fuel
when it gets sprayed in, how the fuel is swirling or mixing and then ultimately burning.
So there's a couple of things I want to unpack for that.
You said how the fuel is injected while a pistons coming up enough for you guys
to understand the home, not like the whole time is coming up.
It's the very, very end.
The last little eighth of an inch to top to the centers
when the fuel actually gets shot in is being shot into that bowl.
We talked about mixing action where gasoline, the fuel and air in general,
I mean, they do have some direct injection stuff now,
but in general, the mixing action happens in the actual runner.
We're here. That mixing happen.
That mixing action has to happen in the piston bowl.
That's why we talk a lot about swirl numbers is that as that our cylinder heads,
we want the head to swirl, get that circular motion.
So it's it helps mix the fuel and air.
So that's actually very important.
Not so much for peak power, but for like emissions and smoke and idle haze,
throttle response, like difference peak power.
It's not really full boost, full load, higher PM.
There's so much like your mixture action going on there, just from the natural,
you know, there's a lot of air moving around at high boost.
And ultimately, I mean, we touched on in a previous podcast,
but I think like when you were at that big, big power,
where you're throwing the injector on for such a long time,
that's ultimately causing a mixing action as well.
When the injector is only open for a little bit of time,
you don't have all the turbulence is going on.
You're really relying on the swirl of the head and a good piston bowl
to help get everything mixed up.
So you don't end up hazing going down the road at these low powers.
Now, one other just I wanted to pull this in more than just diesel.
Recently, we were playing with like a EcoBoost engine had the heads off.
And I noticed that they have a little bowl in the piston now, kind of a little bowl.
It's not like a diesel bowl, but it definitely has its own little chamber.
Some of this direct injection gas stuff, they have a little bowl there too.
Now, I believe they they don't spray on the direct injection on the gas.
They don't spray it right at the end like a diesel.
They spray it kind of on the downstroke of the piston,
but it maybe because it stays on as the pistons come up,
maybe they're making a little room there or maybe that's doing some mixture action.
But actually some gas engines now are getting boosted, direct injected.
They're all have little bowls besides the chamber.
And then they have a little bowl in the piston, but they're catching up
with the diesel technology while the turntables have turned.
Yes. So we normally start with oldest and work our way up.
I think we should start backwards.
So I'm going to start common on work our way back to 12 up.
We always start 12 off and work our way up.
So let's go common road.
One of the things like you may have read or heard is entrant versus non re-entrant.
This is the most stupid terms in technology is like non re-entrant versus entrant.
What are we even talking about?
It's kind of a big deal in the common world.
You're a common road guy, so go ahead.
OK, now it's funny.
Yeah. So I'll be like, I'm fully honest.
I can't never keep those two square away.
I'm pretty sure the re-entrant is so re-entrant is non re-entrant is where it
goes into the middle and goes out re-entrant is where it goes out.
And it re-enters the bowl.
I know it's a terrible way.
I'm pretty sure that's what it means.
But those are the two things we're talking about.
The way I call it is there's an ISB and a QSP.
ISB is your over the road narrow bowl piston.
Like on your six sevenths, that's your narrow bowl.
That's also your 0304 59 piston.
Then you have your QSP, which is your wide bowl.
And that's your 05 or 0407.
And then you're off highway six, seven stuff.
That's a very wide bowl.
Generally speaking, oh, yeah, as you kind of covered, when the fuel goes in,
it's basically you're trying to decide how it's going to swirl through the bowl.
Is it going to swirl from the inside going out?
Is it going to swirl from the outside going in and how you're trying to
what approach you're trying to take with trying to get everything to mix up?
Um, as far as what piston I would do, that one's a really easy one for me
on the six or on your common rails.
The narrow bowl to me is just it's so much better for clean cleanliness on the street.
I will basically always recommend it for big nitrous hits.
They they're a little bit thicker on the outside, so they're less likely to crack.
The wide bowl, though, does have an advantage in that it does seem to make
better power fuel only.
So if you're like a sled bowl class or something where you're like limited
and you're just trying to get everything you can out of it, then you can make
another 20, 30, whatever horsepower on that wider bowl.
But it's just hazy all the time to where it has to be a very specific
build for me to actually recommend it.
I know some people will disagree with that and say like the white
bowl is actually the greatest and everyone has their opinion.
But from what I found, those people are the ones that are running
really massive injectors that are trying to make that big power.
And the reason the wide bowl is not as ideal is because it doesn't
ultimately want to be injected over top dead center.
And when you have a very small injector or a reasonable sized injector,
like let's just say less than 100 percent, you have to in order to get
the fuel in the cylinder, you have to inject for a long enough period of time.
It's very hard to not get that to happen over top dead center.
Either your timing is ridiculously high, ridiculously low.
And so running a narrow bowl, that that bowl design loves to be
injected across top dead center.
And it just, it just runs cleaner.
So I'm going to kind of explain what he's talking about here.
Injected across top dead center.
So in the older technology, the racers, they want all the fuel in the piston
before or at top dead centers.
The pistons coming up, injections done by top dead center.
So that's not necessarily true.
That's like older, older thinking.
Now in the common old world, they call a split, like I run a 80, 20 split
or a 50, 50 split.
And that's like how much before top dead center comes up.
And then 20% of your time is after top dead center and you run a split.
So what he's saying, like this, the wide bowl, if you have to run a split
where you're injecting across as a pistons coming all the way up and going
back down, you're injecting that window, you're going to have some nasty haze
and things like that, which like, if you're under full power and you're
making 1500 horsepower, a slight haze.
I mean, it's kind of almost nature of the beast for power, but go before we
get off of those pistons in general, though, why do we think the factory
had a narrow bowl for on highway applications and they had this wider
bowl that's common in like a stationary generator or a piece of equipment,
something that's not a mission controlled.
Why would they even put a wide bowl in something?
So I'm sure there's a point you're trying to make, you just go for it.
Well, I just, I, clearly there's, there's a fuel economy advantage that they
found on, because if they had a more efficient engine application, that
they could advertise better break specific fuel consumption for a fire
pump or for a fertilizer, they would have done it or a generator.
And so clearly they found something, something economy wise there that
wouldn't meet a mission standards because you want an economy on the street too.
And so traditionally those, those marine bowl or wider bowl pistons or
non re-entrant depends on which generation of vehicle.
There is a, you could say a slight performance or economy advantage that
they found at a moderate, you know, low horsepower level.
We're not talking.
You feel that perhaps the narrow bowl is better for a varying RPM band or the
wide bowl, maybe better for like your generator, your boats, things that can
operate at a constant RPM for a long period of time.
Maybe that's a better design.
Maybe it could be considerations for that as well.
Could be.
100.
And yeah, that fuel economy isn't necessarily the whole band.
Like you're saying in transitional, that could be at your set 3600 RPM that
a generator runs at that is the best efficiencies that there's obviously some
on highway emission things they have to bring into consideration when they're
designing, you know, piston bowls for trucks.
I don't know if there's a better thing.
It's just something to think about to hypothesize.
Is it a better for one RPM range versus a wide RPM?
But we do know, like he talked about the narrow bowl versus wide bowl.
We always go narrow bowl and all of our stuff because it's a very much more
robust piston, having a lot more abuse before it's going to crack melt.
All that kind of this, because it's much more material outside of the bowl,
between the bowl and the edge of the cylinder compared to the wide bowl.
I mean, yeah, it's more robust.
But like I said before, it's also just a cleaner running piston.
So if you're running something on the street or even my like my race truck,
when I'm idling through the pits, I don't want to be this hazy piece of crap.
And so having it be having that narrow bowl just helps everything
mix up and helps everything just burn clean, which obviously is really nice.
So your truck over here that ran 4.99 seconds, the eighth mile,
the factory race track is on factory narrow bowl, six, seven pistons.
Yes, like actual factory.
We did put a coating on them.
We want to try and we're experimenting with some coatings and they are coated.
So they're kind of experimental, but yeah, is the factory cast piston.
Yeah, not a forge.
Like you were talking earlier about bottom end and forged pistons.
These are cast pistons.
And you figured you're averaging it down the track.
Twenty two hundred horsepower give or take.
So I would say like, I mean,
I guess I wanted to talk about the last topic a little bit first.
Sorry, sorry. No, you're good.
But also with the wide bowl, like with the narrow bowl,
there's kind of like a strategy you want to have where either you inject it
very close to top dead center, where it can go from the inside and mix outwards
or you want to inject it, like get the start of injection to happen later.
So that way it goes from the outside and works inwards.
And so that is kind of like the tuning strategy you take on those with a wide bowl.
And I can see why the factory would do this.
If you're fighting emissions, like in those five or six, whatever,
is in your trying to just like you have to have a very wide range of where
you can throw fuel at with pilot and post and main shot.
Like a big one, that big large bowl injector is basically a vat
where you can kind of just throw fuel at it at any point in pilot post, whatever.
As long as it's not too close to top dead center, it will sit there
and it will mix and it will burn.
And so I think that it might be one reason why they did that on those later trucks
is because they needed more flexibility to be able to meet emission standards.
Once they went to a six, seven and had to add all the hardware to make
it pass emissions, they were able to go back to the narrow bowl.
So I don't know if it's an economy thing or not.
Like I haven't seen anything personally.
Yeah, I guess I wasn't really following it first, what you're saying.
But now I'm getting you brought up a very good point from 04 to 07.
They went to a wide bowl for the highway use.
So it's like it's not like it's cut and dry.
The wide bowls, highway or industrial or narrow bowls, highway or industrial,
they've had different flavors that they've chosen over the years.
But if you and if you look at the timing tables between the two factory,
those two tunes, a narrow bowl injector is generally like the factories
kind of all over the place, regardless.
But you look at a narrow bowl, like timing table from the factory.
It looks a little bit more like what you'd expect it to look like.
You look at that wide bowl.
What what what is what you'd expect to look like for a listener?
Like a little higher timing, a higher PM, higher timing, higher fuel
quantities, higher timing.
It looks more like a hill where it slowly ramps up and the different points.
Obviously it's a little spiky.
It's got some high points, low points, whatever.
A wide bowl timing map looks like a freaking mountain range where it's a high,
low, high, low, just like, I don't know what testing they had to do to make
that like make sense to them.
Like how, how like a 20% increase in fuel somehow warrants a complete flip
of the timing, like I don't, I don't get it.
But either way, I think that they needed that, that flexibility just to be able
to meet whatever emission standards they were trying to do.
Because they're trying to do it with purely fuel and no, no, no aftermarket
treatments or anything, not aftermarket, after gr.
Yeah.
But, but anyway, then you talked about like in the gas world, and this is
kind of your point where you're making was in the gas world, you build your
engine, you put pistons in it.
Like here, if it's a real build, you're going to put pistons in this thing.
Diesel's a factory race pistons.
They're, they're made to deal with some crap and they do it pretty well.
Yeah.
Every Cummins piston is even in the 12 of older stuff is a thousand horsepower
capable. None of them are going to bat an eye at a thousand horsepower.
Yeah.
Ultimately, like every diesel piston is about as strong as the block.
Yeah.
Really close.
And then when you start like, you know, ramping up block structures, and you
might start thinking otherwise.
So, yeah.
So for the common old guys, like if we can, if you're calling us in general,
we're going to recommend a narrow ball piston because we just think it's better.
We've had better luck.
We do know fuel only will make a touch more power with a wide ball piston.
And so if you said sled polling, air, air limited classes, you know, power
outer limited stuff, we can use nitrous, then a wide ball makes a lot of sense.
If it's your over the road truck, you want to get a lot of miles out of it
and have a word, good.
We're probably going to say, give up a little bit of power, get your exhaust
clean, enjoy it.
And, and so we also talked about like the efficiency of the piston, whatever else.
However, I don't want people to think that like, oh, well, if it's a 10%
increase or 5% increase, 2% whatever increase in efficiency, that's, that's
fuel mileage, like going down the road.
That's not necessarily true.
Like the reason generally they make more power is because that wider bowl
allows you to run more timing at that big RPM, big power while still staying in
the bowl, like then the, and it's important to stay in the bowl because
that controls the way the fuel is rolling and mixing with the air and you
spread out of the bowl, splattering fuel against the piston wall.
You aren't going to really make great power with that fuel.
And so that narrow bowl works really good.
However, when you start getting super high at timing, you start spraying
on the outside of the bowl and you start losing that efficiency.
So like a narrow bowl, like an 80 split is pretty common and pretty, like pretty safe.
And that's generally what a lot of steps will want to make peak power.
A split means he's injecting fuel 80% before top dead center, 20% after top dead center.
And obviously the size of the injector and everything else plays a part in that.
So considering like pretending like you have a reasonably sized injector for
your goals, 80% split, whereas like the wide bowl will do like a 90% split much
better and much easier.
And you can go even higher.
Like I remember an old setup I had that made really good power at like 130%
split, didn't realize I was doing that, but it did.
And so it's just much more flexible.
So if you're the average Tom Dicker Harry and you have a 2008 to 2018 Dodger
Ram truck and it needs a rebuild, you would just take the exact same
piston that came in their factory style, maybe it's 20 over because you got to
clean up your block, whatever you'd put that same piston right back in there.
And you're going to have something capable of a ton of power.
If you want it, great economy, fuel emissions are low.
Now, some guys are going to be like, well, I run forged pistons on my whatever
my coyote F 150.
Why, why shouldn't I put forged pistons in my 2012 Dodge, Todd?
When I go to put it back to you.
There are some good reasons, honestly, for one, they're very expensive.
Now, Molly has some aftermarket forged, which are much more affordable than
like your diamond ones, and they're pretty good.
They're very expensive and they're cool because they can put any bull you want.
They'll put any compression height you want.
Like you can build a custom piston.
It's awesome.
The problem, the forged pistons and diesels in a diesel cast piston, they have
a steel ring land for the top cylinder ring, piston ring, excuse me.
And it's steel and it's cast into the piston itself.
So the aluminum piston, the steel cast ring land and the pistons and diesels,
they have a lot of, they have to deal with so loading a lot more than
gasoline, they call it a so load, but you've seen it in your oils, black.
I mean, that's what's coming out of your pipe.
If you see smoke, it's so it.
And so those kind of just, they just very abrasive, very abrasive.
And so they do anodized coatings now on forged pistons, which is a helpful,
it's much stronger.
So it is better than like a, just a true force piston that doesn't have any
coating, but you will not get mileage out of that piston, not, not good knowledge
at all.
You'll have terrible wear, the piston will wear out before the rest of the
business, two parts of that.
You saw, you said the factory pistons have a steel ring land.
Obviously forged pistons do not have that.
At least not a lot of them do.
Um, the other part to that, like that, that matters for the conversation is
because diesels deal with that, um, all that soot, they're running a keystone
top ring and that keystone top ring is designed to cycle.
Every time it goes up and down, it helps like, it keeps itself moving.
So it keeps itself free of soot.
It cleans out the, it cleans the soot out of the ring land.
If you've seen old gas engines from a long time ago, sometimes the rings will
be locked up with, you know, or combustion products, a diesel's even worse.
I mean, there's a lot of stuff going on there.
And so that because of that, the ring has, it's moving in that ring land.
It's wearing out the ring land and it's designed to be a little bit loose in there.
So it's just hammering, but, but it's not wearing on a steel ring land.
So you have a, a, you have a steel ring wearing on a steel ring land.
This is in factory, the factory piston steel ring land.
This is a non-existent issue.
Yeah.
But forge piston aluminum, you're not going to, that's not a 50,000 mile piston.
No.
So a forge pistons, they definitely exist in the diesel world.
We have lots of sets here.
We're big believers in them, but that's for a real performance engine.
That's not, you're not looking for mileage.
If there's something is going to go on the street, I would not put a force piston
on anything I plan on driving on the street and, and why?
I mean, you're at 2,200 horsepower, which is going to last forever like that.
Probably not, but the force pistons are stronger.
Fifteen horsepower through a factory piston for quite a while.
Exactly.
Now I want to talk a little bit about keystone ring and rectangle.
A lot of guys don't know that.
So keystone, if you've ever seen an arch or if you ever were in an art class,
that top piece, that's the keystone, that wedge piece.
Well, the ring is wedge shaped when you look at a side profile and that's
what a keystone ring is where regular ring is rectangular.
If you look at a side profile and so that, that keystone design is that
cleaning action they have, and it's not really common.
I can't think of any keystone rings I've seen outside of diesel and all the
engines and dirt bikes and stuff I've ever played with.
Have you ever seen a keystone ring?
Never seen diesel.
So they also have what we believe is a better oil ring.
The little spring, like it's a very different design oil control ring.
Yes.
Control ring is very different design in a diesel than it is in a gasoline.
Even the forged diesel pistons run the gasoline style of controlling that.
And we believe the OE is quite a bit better.
Yeah, I don't know that, but we think that.
So the oil control ring is better.
So you will burn more oil with a forged piston for two reasons.
One, their oil control ring is not as good as the diesel, you know,
the OEM design ones.
And then two, forged pistons grow a lot more.
A factory cast piston is actually a hyper eutectic, which means it has
silicon mixed into the aluminum, which means it has more thermal stability.
It doesn't grow as much with heat.
Doesn't shrink as much when it gets cold.
A forged piston, there's a couple of different alloys of aluminum.
There's kind of two main alloys a lot of guys use, but both of them grow a lot more.
One has more silicon in it, so it's more cast like.
That's kind of what Molly is using on them.
But like diamond and some of these other companies, they're using the stronger
forging because they're going for ultimate power and they have more growth.
Yeah. So our race engines, we run very, very large piston, the wall clearances.
I mean, and you have to, otherwise every time you put your pistons out and be
scuffed by pissing while you're talking, how loose the pistons fit in the engine.
When you're checking, you can rock them back and forth in there.
Like you can physically build your engine, grab that piston and rock it back and
forth like a lot.
I mean, you can move a little bit on a cast one, but it's very noticeably
different how much more piston the wall we have to run.
And so that wide piston, a wall on the forge piston, that's a downside for a
street truck. One, it'll make a little bit more noise, build a noisier till it
warms up. Two, it's going to burn more oil because it's moving.
So even if it had an equal oil ring, I don't even know if an OEM style
oil ring would handle that much rocking.
It might destroy.
That might be why they're not even using that.
And then three, because the piston is looser and it rocks more, it's going to
wear the bores out faster, where the ring changes direction.
It's going to wear the engine faster.
That's the other reason it's not going to go a million miles is, but it will
handle a crap ton of RPM without rippling the guts out of the bottom.
Like they are superior for that.
They also, the other final little thing, those factory cast pistons, when you
get into these six sevens, they have an oil cooling galley cast into them.
They have a hollow place and the engine has a J jet that sprays oil constantly.
An oil nozzle on the bottom of the piston to cool it.
And that's kind of how they can maintain this, this higher engine
temperature under load than where the aluminum could potentially melt and fail.
They have that a forge piston does not have a groove like that.
Cause it's a forging.
You can't, you can't machine a whole canal through the.
Yeah.
And so that's, and so that's kind of the, the main difference there.
So when you're Tom Dicker, Harry, and you have a, like, like I said, a pretty
much, let's be honest, if you're Tom Dicker, Harry, you have any model year of
Cummins, you're going to run a cast piston on the street.
It's better period.
Now, as you go down to like the five nine common rail, you do have the option
of steel pistons, Molly makes a steel piston.
I don't know why they've never offered it in the six seven.
And I don't know how wildly popular it is.
I know some guys ran it, but it's never seemed like it's been this
wildly popular option because they're very expensive.
I've never ran one.
The, I mean, and then steel is a proven technology.
It's kind of newer in the Cummins world.
There's not a lot of guys doing it.
The Ford power stroke guys out there, once you get to, I think, 2021, they're
all steel from the factory and it's a very common upgrade.
All were, but like certain model year, certain, maybe the higher output
ones or something, but it's very common for people with older six, seven
power strokes to upgrade to the new steel pistons and you can run much
tighter piston to wall because they are, they don't expand like an aluminum.
Even your cast pistons, you're going to tighter with that.
So that's, that's, I mean, we can put some numbers on there.
So let's say the smallest you'd ever be in a forge pistons, probably
eight to 10,000ths, pissed in a wall, a cast piston.
I've seen some of those spec down at 4,000ths, pissed in a wall, pretty
commonly steel, that's like 4,000, like stock engine, like stock engine, not real
power. You're talking about any, but I'm just saying how small you get just
like a forge piston. I've seen them specced down to eight, but generally
guys don't run them for big power that tight, but as low as eight as I've seen.
And then on a steel piston, they recommend 2,000ths piston wall.
One and a half is the tightest they've seen those spec.
I mean, that is like, you talked to any engine builder, like you want to, what?
One and a half, 2,000ths piston.
Well, they're like, no way.
But if you have a steel piston that grows the same rate as your cast iron block,
it doesn't need, it needs clearance.
That's all it needs.
And so there could be a wear advantage there.
I know steel pistons are a lot more popular in semi truck applications.
But, but like, so we really have not done much with them here.
I just never had a good source of there out there.
They are there was a steel six, seven piston.
We were to try them.
Oh, you're stuck with the power level of the block.
So it's like the pistons can maintain with the block and hold before you start
modifying the block as you drop down the cut to VP 44, there's just one piston.
All VP 44s, there's no option.
Oh, there, there's two models of them, but there was a really high output,
just the high output in the standard.
So they're a little different.
And it's just the, the bowls bigger on the standard output and they're a little
lower compression.
But so that's the preferred VP.
If you're making power purely because you can run more timing and still keep
the fuel in the bowl.
So you can make a little bit more power, the VP with a standard output piston.
But we're talking two millimeters.
It's like most people don't even know that.
So Meyer didn't know that.
I did not know that.
I used to be a VP guy.
I used to be a big blue 24 valve.
And we are now, I'm a now VP guy, dude.
Willard has converted.
You have drawings of VP pistons, cutaways on my computer desktop.
So I could just, you know, reference them.
Everybody needs that.
You talked about compression.
That's something we didn't mention with forged pistons.
You can also, because you can design your piston, you can get a very low
compression piston.
In the older Mali cast pistons, you have options like in the 12 valves for
lower compression pistons.
I don't know that you do in the common real world have lower compression
pistons from the, from Mali or things like that.
Like power pack pistons give you low compression.
I've never looked.
No, I don't think Molly does anything.
I mean, obviously they call low compression options because they have valve
relief ones, but yeah, but real piston design change.
So now we're down to the 12 valves.
This is kind of like we, where we cut our teeth.
Will and I, and this is, and Myers played it quite a bit too.
There's the standard bowl, which comes from the, from the, uh, your trucks.
It's very narrow.
It's really small bowl compared to anything else.
And then it's very common upgrade for us as we put in like the non-intercooled
first gen, like early 89.
So when you get pre 91, they were non-intercooled.
So the Cummins on highway, they're not intercooled.
They had a wider, pretty wide bowl, but they, uh, they're also high compression.
They're 17 and a half to one.
And that was, like I said, a really, just a really popular, um, really popular
piston bowl that we like a lot on, on 12 valves.
It's a good ratio of big enough bowl to make power and compression ratio.
That's what's in Vindy with the blue collar truck.
We didn't even know that.
So we swapped the head, somebody put non-intercooled pistons in it.
And, uh, yeah.
So they run clean with, uh, with the right injectors and tuning, great power.
And, uh, for most 12 off stuff, we kind of steer people that direction.
We have played in the past also with the Molly power pack pistons with lower
compression down to 13 to one.
I mean, quite a bit lower compression.
I think the lowest of guns, like 12 and a half to one was a total dog.
We are not in love with low compression pistons.
We used to be, cause that was like the, that was the norm.
That's what you got to do.
If you're going to run higher power, higher PM, lots of boost.
You got to run a low compression pistons and maybe before we had common
rail blocks and the guys were in the 12 out blocks that maybe in the
play to keep them alive, run a low compression piston and then your block
doesn't split.
That's a very possible thing and why they kind of went that direction.
But now that we're most of the horror guys are using six, seven blocks and
P pumping them for the comment for the, you know, P pump guys or common rail,
except for Will, who's just breaking 12 out blocks left and right.
You know, I was thinking of deckplating a 12 out block though, cause I was
like, just, just, just to flex on everybody.
That is a sin.
So when you're talking about like the ultimate, like, say the high
level of sled pulling where, I mean, they're throwing stupid fuel at the cylinder.
You, you're injecting a solid into the cylinder before the pistons all the way up.
You're kind of artificially increasing your compression ratio, because
you're displacing air that compresses with fuel that doesn't.
And I'd never done the math to know like exactly how much that's affecting it.
But just to say that we don't believe in high compression or low compression.
If you're doing something like that, there is a need, there's a reason
to exist.
We just haven't really experienced it.
But if you're on the street doing reasonable street things so far, higher
compression is always just better.
It drives better.
Like that's something I always go back to is that I think anyone, like someone
like tries to say, Oh man, this truck makes 800 horsepower.
You should drive it when I drive it.
I know what 800 horsepower feels like.
I trust you.
It probably makes 800.
I want to see how well it makes, how well it drives around.
Well, be able to make 800 if it's a smoky dog.
Cool.
I'm glad that it makes 800, but it's a terrible build.
Yeah.
But if it's clean, I can drive it on the street clean and just it's peppy.
It's fun.
It comes up good.
I don't have to smoke out any intersections just to get up and going.
Like that's a good build.
That's a fun and so when to build something like that, you like higher compression.
And that's a huge part of the six seven crank that we do with the six one
stroker, you're bumping your compression ratio up a bunch.
And so like my dad's is like 19 to one.
And that was with a domes.
Yeah, I built him a six one stroker.
It's got, I was, that was like early, early days of six one strokers.
And so I was worried about the 21 or 20 to one compression.
It was going to have, I did the wide bowl.
So I did a two 15 bowl on that thing and it was a tow truck.
It's like, it's not, it's got 18 degrees of timing.
Like, yeah, it's fine.
Like it's, it's fine for what it's doing.
Um, but it runs really well.
It runs great.
It's super clean, super peppy.
And that compression is a huge part of that, I'm sure.
So, so the 12 hours has been around forever.
There are, so they started with the non-intercooled first gen bowl, which is
kind of some people call it the Mexican hat bowl.
Cause it's got kind of like a little dome in the middle.
And it kind of looks like a little bit.
And so that was like a common.
They called it the Mexican hat.
I've never heard that before.
That's what they called them.
Then in 91 and a half, and they went intercooled, they kind of went to a
re-entrant style bowl where it's got a, the dome in the middle looks almost
like the head of a mushroom or something.
It's got a little bit, it looks a little funny and it's got a lip on the bowl
where that first gen, it's just angled, but it's open.
There's no lip.
It's got a little bit of an angle.
The, the intercooled ones that, and it's still pretty good size, but it's,
it's smaller than the non-intercooled and the compression ratio.
You know, all of them ended up there around, you know, 17 and a half to one, 17,
three just depends.
Then when they went into like, uh, 94 and they went into the actual P pump,
12 hours, the bowl got a little bit smaller.
Again, probably some emissions reasons or something there.
And then in 96, they made a little bit of a change, slightly bigger, smaller.
They moved the height of the ring.
They moved it up closer to the top of the cylinder, which that early first gen
non-intercooled, the ring is way down.
It's like 14 millimeters down.
And so the rings very protected from heat, which you'd want in a non-intercooled
application, cause they're just, they're just kind of a dirty hot engine, in my
opinion.
Anyway, they moved it up, but the further you ring is down, the more trapped
gases and weird combustion products you can get between the ring and the
top of the piston, and it's just not as good for emissions.
There's, there's just, there's problems with that.
It seems like as they get newer, they move the ring higher on the piston and
performance guys generally move the ring down to protect it.
If they're, they're hitting it or they move it up.
If they're trying to make the piston shorter and some of the gas world, they're
trying to move the route.
Anyway, there's tons of strategies there on stability, the piston, but long story
short, they, over time on the 12 hours, they moved the ring higher and higher.
Then you get into like 96, 97, when they went to the 215, the bowl is even a
little bit different.
So it's like, there's tons of little variations, but we've kind of found that
if you have an on highway 12 valve piston and you want that style, that, that
OEM style, the 215 is the most common one made in the aftermarket and they're
close enough and the rings.
They moved the ring land down on the 215 again.
So it's, it moved it down, which makes it a great six one stroker piston, because
you don't have enough meat on top of the ring land on like a 180, 160 piston to
be able to machine off and have like good margin there.
So, I mean, you can do it, but it's not ideal.
It's not ideal.
A 215 bowl, they moved that ring down the two millimeters or whatever it is to
where you deck it, the 80 thou, it gets you pretty close to what a 160, 180.
And I would say, I don't know exact, I can't remember, but I think the furthest
rings down is 14 millimeter on the earliest ones.
And the shallows I've seen, I think it's like 9.9 millimeters down.
So basically you've got about a four millimeter difference in ring heights.
And, uh, when you're doing a six one stroke, you're taking 80,000s off the
top of the piston, you know, if you're using a factory length rod with a six,
seven crank and so 80,000s, what's that two millimeters, two millimeters.
So, so you're, you're well within, you know, what they've already proven is good.
It is good, but that's kind of gets you through all those years at 12 hours.
And so because we like a little bit wider bowl, a lot of guy, we recommend that
non-intercooled first gen piston.
It's just a very good piston to do that.
In fact, Molly and their motor sports power pack pistons, they have two versions.
They have one with that bowl design, it's the height compression, but they've,
they've reduced the, uh, the top of the piston a little bit.
They've changed the pin height.
And so they're about 16 and a half to one instead of 17 and a half to one,
like a factory, but they took that bowl design, they just changed the orientation.
And then the lower compression Molly power pack, those have the early Marine
bowl, which is even wider, lower compression.
And, uh, I mean, we're getting on a whole tyrant here, but there's a ton
of different piston bowl designs on the 12 valves.
It is interesting how much they changed there and it's kind of gone away.
They kind of got figured out, I guess, for what are we going to do now?
Maybe it's because you have the aftermarket emission systems or the after,
after turbo, I mean, like we've said, like a 12 valve is tuned by the parts
you put in it.
They were having to tune the truck with the pistons very true, very true with
common rail, like, ah, here's throw this bowl at it and we can, we can tune
our way around it.
Yeah, it's very valid point.
I mean, don't, don't undersell that.
I mean, there was very little they could do to tune a 12 valve.
They had a torque plate in there and a boost reference AFC foot.
And it, the timing was pretty much fixed, you know, and so you have that,
you get a modern common rail where they can change the fuel pressure.
They can change the, the fuel duration and the start point.
They can do a lot of changes to make a standard bowl work the same, you know,
or meet their application.
Another thing I could say we're playing with when you're playing on
Meyer's truck is coatings.
It's very common people upgrade their pistons.
They want to talk about coatings with different coatings, different companies.
I wouldn't say we're experts yet.
We were definitely like getting into that as well.
We do like coatings, which I would say like early on, we were kind of a naysayer
on coatings because nothing would actually hold up.
You'd put a coated piston in, put the super special, special, whatever
crap in there you make, however many dino hits ultimately it blows up and you
take it apart and there's no coating left.
It all like vaporized.
Yeah, you're like, cool.
I'm like, I'm glad I spent however much money on that and slowed down the
build and did all those things.
Well, we are trying out some new stuff, which is much more promising so far.
Yeah, it's excited for it.
Yeah.
Now, coating on the skirts, a slick coating, that's common.
Normally there's an oil film on the cylinder wall that the piston rides on.
And as far as factory coating, the Marine early 12 out pistons, they had
coating Teflon Teflon on the skirts.
We're talking clear back in the 80s.
They were doing this.
So it's not, it's not new technology, but on the highway applications, the
first time I saw coatings was at 13 or 14 on the six, seven pistons.
Maybe it's 2014 15 has it.
I don't remember maybe even 2015 and they have coating and I know the new
like 19s and stuff, they have coating.
And so the factory is definitely putting coatings on the skirts.
And this isn't like you get in the popular LS engines, they have coated skirts.
So it's, it's like a lot of the OEMs started really getting heavy on
coatings and at least with, with a GM and the, the, you know, late 2000s.
And then with Cummins, it seems like about 20, you know, for highway use, it
wasn't until 2014, 2015 model years, they started putting coatings, but that
does seem to be a little bit of a benefit.
Cause sometimes your piston gets loaded hard and pushes through the oil film
and that, that, you know, slick skirt helps a little bit.
I will say, you know, no coating can survive improper clearance.
I would say the most of the damage we see from coatings is probably due
to not enough piston wall clearance.
I don't think, like you said, you're going to side load it.
The 12 valves are worse because of the offset bowl.
And so it seems to kind of push it over to the side a little worse than the common
rails, but I mean, we've had race owners come out with very little
damage to the skirts at all.
Yeah.
Yeah.
And other ones that were way or smoked, like, well, there was enough clearance
there.
And I mean, coatings are great, but nothing's going to survive not enough
piston wall for what you're doing.
So make sure when you're building your engines, that you have enough
a piston wall, you know, whoever's building it for you or working with you
or maybe you have enough knowledge, all that's for happy to talk to you.
But you do need enough clearance for what you're doing.
Yeah.
And I should, and I should clarify, like we talked about how my engine was a
little tighter than I wanted to be.
So we coated the pistons.
Looser than you wanted to be.
No, my, my, my engine was tighter than I wanted to be.
So I coated the pistons.
I was talking about the top of the piston to keep the heat out of the piston.
I'm not going to coat the sides of the piston to somehow fix a misclearance
issue, like you're saying.
And so that should be some distinction.
Like, like we're talking about, like coatings not actually holding up.
Like that's, I'm, I'm referring to the top of the piston.
Actually, we've had on both, like on the side where it just all flaked off,
like literally flakes in the oil pan.
Like, well, I was stupid.
Didn't wear through.
It just flaked off.
Um, but yeah, anything we can do to keep the heat out of the piston and keep it
in pressure, pushing the piston down is a benefit mileage, power, all that stuff.
I mean, that's, that's a big deal.
So, so, I mean, so then I did want to kind of hit a little bit.
So we're talking a little bit about piston to wall clearance.
Um, I feel like in the past, when we were developing 12 of engines, we kept
budding rings and scuffing pistons and we had to learn to go looser and looser
clearance.
And one thing I kind of, of this theory, we, we started getting very loose
piston to wall clearance, like, like obscene.
We're talking like over, I mean, I had some that were like 12,000
piston wall on a cast piston that doesn't hardly grow.
And back then we did not have a nice home where we could do a torque plate
home and I feel like with 12 valves, the board distorts a lot.
I think you need more piston to wall clearance.
When you do not have a torque plate home, you have to open it up bigger
because the board distorts and gets tight in the wrong places where we were
having trouble.
And so back in the day, I would say, if you were at 1000 horsepower, you needed
10,000 pistons to wall or maybe even a little bit more to be, you know, if
you're going to get it hot or do burnout contests or just, you know, really
abuse it at 1000 where I found with a torque plate home, we can probably
tighten that up 2000 on the piston to wall and it will survive.
And it has better ring seal, it makes more power.
And so for a street application, you're better off to stay tighter on the
clearance as long as it's loose enough that it doesn't rub.
With a good torque plate home though.
A torque plate home and a proper home.
That's true.
That's a big deal.
Like getting your valleys deep enough to hold the oil, but not so deep as
going to burn oil.
Like you've learned a ton about honing.
This isn't a piston bull design, but it's directly relates to how
piston rings and how long your pistons will live.
So maybe talk quickly about your home that you've been doing.
Yeah.
So the cross hatch in the cylinder holds the oil and that's what lubricates
the piston.
If the valleys or the, there's peaks and valleys when you, when you, when you hone
something and when your engine breaks in, the rings knock all the peaks off and
all you're left with is the valleys.
And so a lot of times people used to call it a plateau home.
And what they would do is they would, they'd hone it and get it really close to
size and they go with a really fine stone at the end and do their last
thousandth of clearance with the fine stone.
But what we found with modern pro-philometers, things that it can
actually measure the surface is whatever stone you set the size with, that sets
the valley depth.
So if you finish with a really fine 400 grit stone, you have almost zero
valley depth in there.
It's even worse on a Cummins application because the blocks are pretty good hard
iron Cummins and power strokes are even harder iron I found.
And so if you have like old, they call it like, you know, stones, you know, the,
the breakdown instead of diamonds, the stones don't get as much valley depth
because the block material is hard, more carbide particles and stuff.
Just the iron is better.
And so you need a hone that has, that can get you to size, but it needs to be a
fairly aggressive grit when they get there.
And then what you're doing instead of letting the rings where the top peaks off,
which wears the coating on your rings off on your pistons, which is another,
another whole topic, but there's like special coatings they put on the rings
to help them hold oil and that wears off when it breaks in.
And so if you can pre break in the engine with some diamond CBN stones that can
actually do an extreme plateau and they actually knock the peaks off,
you're left with the valley depth you want from your aggressive hone,
but then you have a smooth surface finish.
And you can see that on the profilometer graph.
Like when you do a before and after like you do your hone,
then you do the extreme plateau.
It's like your visor is still there, but it's, it's flat wall.
It's not this jagged wall your rings are going over.
And this is microscopic stuff, of course,
but it's just measured in microns.
So like a good valley on like one of race engines, over a hundred microns deep.
I mean, that's pretty small, but you start looking at microns.
Yeah, that's millions of a,
a hundred millions deep.
Yes, very deep, but, but it matters.
It actually, it's, it's known now after that's what's fun.
It's, we live in a time where it is known what needs to happen.
We have the machines like you have, we got the hone here,
so we could do it on our race engines and the engines we build.
We have this capacity, but then that, that holds the oil there.
And that's what allows you to have regular piss in a wall clearance.
Cause as soon as your piston skirt pushes through the oil and rubs,
it makes heat and it grows even more.
And it's like a cascading effect that goes downhill quickly.
And so that's why you need clearance, but I feel like with a proper
extreme plateau hone with good valley depth that's holding the oil
and with torque plate hone, so the board is round, you can go tighter,
which means there's less piston rock, which means better fuel economy
because the ring seal is better longer engine, longer engine life
because there's less, there's less rock in there.
And your rings didn't get the coding word off.
And there's less friction there.
The more true it runs, all of that goes together to make more economy,
more power and more reliability.
And so if anybody asks us like piss in a wall clearance,
I now tell them it depends.
Is this going to be done with a torque plate?
All right.
Is it a sun and hone?
Okay.
Do they have the upgraded to the diamond stones in the sun?
And are they using typical stones?
If it's a new rattler hone, well, with a torque plate,
yeah, you can go a lot tighter.
Yeah.
So yeah, definitely on your build varies a lot.
So anyway guys, I think that's about our time.
I think we kind of got through our piston knowledge.
Hope you guys enjoyed this episode.
It's always fun to talk about, you know, nerdy stuff like this.
We like pistons.
We like Londoner stuff.
And so I hope you're still here.
If you're here, we appreciate hanging out.
Yeah.
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About this episode
The Power Driven Podcast dives deep into diesel piston design—why the combustion chamber (piston bowl) matters for mixing, emissions, smoke, and idle quality. The hosts compare narrow vs wide bowl (re-entrant vs non re-entrant) and explain tuning concepts like injection timing splits around top dead center. They argue narrow bowls typically run cleaner and are more robust for street/over-the-road builds, while wide bowls can make more fuel-only power in specific racing classes. The discussion also covers cast vs forged vs steel pistons, piston-to-wall clearance, keystone rings, and why forged pistons often hurt mileage and oil consumption on street engines.
Pistons are one of those parts everybody installs but not everybody actually understands. Todd, Will, and Myer break down piston design from top to bottom, and if you have ever wondered why there are so many options or which one belongs in your build, this is the episode you need.
They start with piston bowl design and why it matters more than most guys think. Narrow bowl versus wide bowl, reentrant versus non-reentrant, and how each design affects the way fuel and air mix inside a diesel cylinder. Because diesels fire fuel directly into that bowl at the very end of the compression stroke, bowl geometry has a direct impact on combustion quality, smoke, and power output in a way gasoline engines never have to deal with. Swirl numbers get covered too, and why that circular mixing motion plays a bigger role in emissions and haze than it does in outright peak power.
The conversation moves through piston options platform by platform. Common rail, 24 valve, VP44, and 12 valve all get their own breakdown. The guys talk about why they almost always steer people toward a narrow bowl for over-the-road use, but also when a wide bowl makes sense, like sled pulling and nitrous-limited classes where you are chasing every last horsepower.
Cast versus forged is a big chunk of this episode and the guys do not sugarcoat it. Forged pistons are stronger and handle RPM abuse better, but the increased wall clearance required, the wear characteristics, and the oil ring differences make them a poor choice for anything that sees regular street miles. They even mention their factory 6.7 cast pistons surviving a truck that averages 2200 horsepower down the track, and what that says about how capable a properly built cast piston really is.
The 12 valve guys get their section too. Stock pistons, the early first gen wider bowl swap, and why the shop has largely moved away from recommending low compression pistons now that six seven blocks are the go-to platform for high-output Cummins builds.
Piston coatings and cylinder honing round out the episode. The guys cover their coating experiments on Myer's race truck, what coatings can and cannot protect against, and why proper piston wall clearance is still the thing that determines whether any of it survives.
Subscribe on YouTube and follow the Power Driven Podcast on Spotify or Apple Podcasts so you do not miss episodes like this one.
Everything from pistons to full build components for your diesel is available at PowerDriven.com. If anything from this episode sparks a build question, the team there can point you in the right direction.
