Field Report: Why Not Fit The BIGGEST Exhaust Manifold You Can?

In the motorsport world, there's a tendency to believe that bigger is better, and this certainly is a belief when it comes to exhaust manifold sizing, particularly for turbocharged vehicles.

I'm here with Ben from R-Tech to talk about their design trend and finding out that maybe bigger isn't always better.

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So, ben, for a start, bigger is better.

Why has that been the trajectory that a lot of people have taken with designing exhaust manifolds?

Well, I actually think it was started a bit earlier on in the 90s, tuning with HKS and Grety.

They all had their sort of certain pipe size that they used and they would always use the same pipe size for no matter what turbo manifold it was or what application.

And back then it was all about making as much power as you could on pump fuel Japanese pump fuel so they would sacrifice everything to gain as much power with as little back pressure and as top ends.

That's why even the turbos back then had very big turbines versed the compressor cover because they were limited on boost due to the fuel.

But they wanted to get as much power so they reduced the back pressure as much as possible.

So they had huge lag.

Right then the industry, when it came to fabricating manifolds, would use normally inch and a half or inch and a quarter inch pipe.

Now when we're looking at designing manifolds, we're trying to optimize a drivability for the car, not necessarily peak power, because most people in the industry or using the car is for the street.

Now we find that when you're driving a car on the street the rev range is more so 1500 to 5000 rpm, not above that.

Now what we look at is we try and design the runner size for the application of the manifold and the engine specifications.

So, for example, sr20 that we design uses the 33 millimeter ID runner, whereas our American KA24 Nissan runs a 36 millimeter ID.

So you're not stuck with one size fits all.

Yeah, so we change every manifold.

We're not using the same size, so some of our Honda stuff is a bit bigger, so we go up to 38 millimeter and some of our GDR stuff is 36, some of it's 33.

Now that's due to the capacity per cylinder and also the compression.

Alright, so where do you come to the conclusion in terms of what runner size suits a particular application, like you've just said, is is there something to do with your turbo sizing or head flow port sizes?

The entry to the turbine housing I mean, there's so many elements here that come into play the power band and, as you mentioned, the rev range.

You want that power band and give us a little bit more insight into those considerations.

So, for example, an inch and a half with a three mil wall thickness is has a 42 millimeter ID runner.

Now, at precision 6466.82

, rear housing has a 44 millimeter ID at the beginning of its scroll.

So for me I was like, well, why would I be running four runners that have 42 millimeter ID versus the turbine as in a 44.

So the entry of a precision turbo is a 50 millimeter ID.

So what we're looking at is how much flow the cylinder head has per cylinder.

So most, most ported race stuff will go from 180 CFM maybe 250 on a maximum drag application.

So we're talking here about what the exhaust port will flow.

Yeah.

So people will say, oh, my exhaust port size is a certain diameter.

It must.

The runner must be that size also.

But what we look at is, well, how much does the exhaust port flow, not how big the exhaust port is.

So yeah, there's no point having a runner that can flow 350, 400 CFM when the runner itself only flows 250 or 220.

Okay, I mean that makes sense, sort of matching the flow capability between the exhaust port and the runner.

So what happens with the traditional manifold, which is massively oversized relative to its flow requirements?

Is this just going to add lag, and how do you sort of quantify how much lag there is?

Yeah, so again, one of the couple of key rules that we look for is high flow and low internal volume of the manifold.

So this is actually validated by the industry through the OEMs.

Like you look at McLaren, nissan, all the guys that are doing high-end turbo cars they're trying to reduce the volume of the manifold to the point where a lot of them actually bolt the turbo to the head and design the head to be the exhaust manifold itself.

So, yeah, so what that means is in the real world is how it feels whilst you're driving your part throttle, acceleration, and how that correlates to how much you push the pedal down, to how much acceleration you get in return.

Now, because this whole industry in the aftermarket has sort of been brought up with this bigger is better mentality, are you facing sort of an uphill battle changing that message in the aftermarket and getting people to understand your message and buy a manifold which on face value looks tiny?

Yeah, what we find is, if we make a manifold that works well, has good response, is easy to fit and is readily available, the workshops and customers, it just follows.

Are there any downsides?

Is there a power level above which your runners are actually restrictive, or what's the take on that?

Yeah, there's certain manifolds are designed for a certain power range.

For example our Evo manifolds and SR manifolds.

They both run a 33mm ID runner.

A lot of workshops and customers and people thought that was going to be a limit of causing back pressure.

But even our four cylinder ones are hitting 800 wheel horsepower with zero back pressure.

So the way I say it's easy to look at back pressure is what heats up first in the system and it's the scroll of the turbo and the heat works its way back to the head.

So that means the pressure is building up at a greater level and temperature at the restriction, which is the turbo working backwards.

If the manifold was a restriction it would be having a hot spot at the beginning of the runner, not at the end of it.

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If we take it to extremes, I'm guessing you probably wouldn't be recommending these manifolds for a 4G63 drag car that's aiming for 1400 horsepower.

Would you be reconsidering your sizing at that point?

And obviously that's not relevant to 99.9%

of the market.

So I'm not taking away from what you're doing.

I just want to get the fact that there is potentially a range here.

Yeah, 100%, I totally get that.

You should try and make a product for the application.

We actually have a 4G63 Big Daddy manifold coming out which is specifically designed to suit the 70mm turbos.

So you can run up to a 7675 or 8385 or a G42 compact or a G40.

And that actually that particular item, is designed for a street car.

It can run AC, four inch downpipe air intake, full size radiator.

That one's coming out later this year.

But yeah, I 100% agree with there is a certain range that a turbo, otherwise you're compromising.

Everyone says what about this, what about this?

I'm like well, there's a you have to compromise the entire manifold for some reason packaging costs, availability, complexity, casting capabilities, like we've been developing casting for over 10 years now.

The process in itself is extremely complicated.

So that's another compromise that we have to look at with how we're designing them.

Since you've raised the manufacturing process, casting, the majority of the aftermarket manifolds, or mainstream aftermarket exhaust manifolds, still tend to be fabricated.

Why did you go the casting route and can you give us sort of the pros and cons list between fabricated versus cast manifolds?

Well, we're trying to make a product available to suit most people's needs.

Like people say I've got to get custom, is custom that?

Well, your intercooler is not custom.

Your turbo is not custom.

Your wastegate is not custom.

Your intake manifolds not custom.

We're just trying to make it a bit more readily available for the workshop to increase the throughput.

So not waiting for that part to be made.

Now there is a compromise with casting.

We can't change the design or make a specific, specific version for your car.

Like.

We're close to a 12 month development time for every model.

So, yeah, we can't make a change quickly.

Like if we make a revision to the tooling, we're probably looking at a delay of four months.

I mean that makes sense, talking about the material that you're using for these manifolds.

Again, I'm guessing there's a range that you could select for an exhaust manifold and obviously it has to handle the heat.

So what have you gone with?

and again, pros and cons 10 years or probably 12 years ago, we were casting in 304 stainless.

To be honest, we've never had one issue with that at all.

We use 347 now.

Another thing we're also we are experimenting with Incanel.

That's something we hope to release at the end of this year.

They're very, very expensive but very specific applications.

It's the heat range that is safe or applicable to the manifold.

So, for example, stainless 347 is like structurally safe until about 820 degrees C and then the strength of the material drops off dramatically.

So at roughly 820 degrees it's about a third of its room temperature strength.

So, and as you go to Incanel and titanium, they all have much higher ceilings but the cost is amazingly expensive.

Yeah, I guess again it all comes down to that compromise.

I imagine 820 C would be more than sufficient for the majority of applications, but in some dedicated motorsport scenarios you might be starting to push the boundaries beyond that, correct, yeah?

One thing that we've noticed with the installation of a lot of manifolds and feedback and just designs that we see people doing fabricating with the parts, is it's thinking that because the parts are aftermarket, it's indestructible.

So we also recommend people always brace the turbo, like we always say well, look at how your OEM turbo was made, produced and braced and you do the same for an aftermarket.

Doesn't matter if it's our manifold or any other manufacturer out there.

Always expect there to be excessive load because you've got exhaust temperatures have probably doubled what the OEM was right.

So you've already weakened the material over what the OEM was and you're putting it through a lot more abuse limiter bashing, drifting, all these things.

So that's what we sort of.

We are developing kits to try and make it easier for people to do that.

But that's one thing.

We say that probably they should be taking more care on the installation.

That is a tricky one, and you're 100% correct.

It's very easy to forget the fact that that manifold is supporting quite a significant amount of mass with the turbocharger, maybe wastegate the front pipe as well, and bracing that is really important, no matter whether it's a fabricated or a cast manifold for reliability.

Obviously a tricky one, though, because a solid brace for the turbo and manifold doesn't allow any movement and obviously the manifold will tend to change dimensionally as it heats up correct.

Yeah, I'm always seeing people not putting the flexes in the right spot.

So I always say to people try and put the flex roughly one foot away from the turbo, right.

So yes, you would be getting movement of the whole system, but then at the same time you've got a brace.

In my opinion is better than no brace.

So, and then putting a flexible brace is, we'll say, very complex for a normal person to fabricate.

We've always tried in-house to do a brace that sort of uses rod ends at both ends so that it can actually have some movement.

It's not a perfect solution, but better than solid.

I just want to also talk about the wastegate integration, because this can really make or break the boost control with an external wastegate.

So what's important to understand with that?

Well, since we're not restricted by a certain collector design runner size, we actually design every wastegate position to suit an application.

So we always design our stuff to be able to run a plumb back wastegate and we always put the wastegate in a position where it's fine to be both externally vented or plumb back and also clearanced everything, clearancing the chassis rails, probably tight to the block.

Yeah, so in terms of flow, that's the biggest thing that we probably see with boost control, not the actual wastegate size.

So if you look at the flow of the wastegate compared to flow of the manifold, that's probably the biggest thing that's out with our different manifolds and wastegates on the market.

To date we've actually had no wastegate boost control issues whatsoever.

That is a problem I do see with a lot of aftermarket manifolds where they really haven't prioritized flowing into the wastegate, and it does make such a difference when you're trying to tune that boost curve, luke being great to get some insight into the product.

If people want to find out more about it, how are they best to do so?

Yeah, just artechperformancecom.

That'll take you to the closest website to Suture.

Perfect.

Thank you very much for your time.

Thanks very much.

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Field Report: Why Not Fit The BIGGEST Exhaust Manifold You Can?

BMW G42

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