Exploring the intricacies of tuning a turbocharged 2JZ-GE engine, Mitch from Haltech discusses the balance between power and reliability. The conversation dives into managing torque, the importance of rod bolt strength, and the challenges of optimizing ignition timing. With a focus on a specific Supra setup, they detail how boost control is used to maintain a flat torque curve while ensuring the engine remains within safe limits. The episode highlights the technical nuances of tuning for performance without compromising engine longevity.
But like anything, if you know the weaknesses to watch out for it is easier to manage and avoid them as Haltech's Mitch Smith explains in relation to this 780whp 2JZ-GE being used in a time attack applications.
Using modern aftermarket ECU systems one tool tuners have on hand is torque management, and Mitch explains how vis boost and ignition control, he can maintain a flat torque curve with the goal of mechanical sympathy on this stock 2jz bottom end.
With a stock bottom end, build cylinder head, Precision 6870 turbo pushing 25 PSI at max boost this Supra is limited to around 7,500 rpm in order to help keep the stock rod bolts intact and the car doing laps.
"...nd us has a stock bottom end out of a very old NA Supra, so it's a 2JZ GE bottom end in this, probably go..."
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Usually, when it comes to engine tuning, most people would think that we just tuned the engine to make as much power and torque as we possibly can, but the reality can often be somewhat different.
We're here with Mitch from Haltech to talk about how we go about managing engine torque.
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So, mitch, for a start let's talk about the engine in the super behind us and why this is even a consideration in terms of limiting or managing the torque and power output.
Yeah for sure.
So John Super behind us has a stock bottom end out of a very old NA Supra, so it's a 2JZ GE bottom end in this, probably got a couple of hundred thousand Ks on it.
Okay, so this is still turbo charged, even though it's running a naturally aspirated block.
Yeah, correct.
So it's got a built cylinder head on it, precision 6870 on it, all of the intake and exhaust mods that you'd have on a circuit car, but, yeah, everything below the cylinder head still as Toyota intended it.
Alright.
So there's a couple of considerations there with the 2JZ that I just wanted to mention.
So obviously naturally aspirated with stock piston, it's a cast piston.
Strength is an issue there.
Compression ratio is up, although I'm guessing you're probably running on a good fuel like E85, where that is not necessarily an issue.
We've got corner rod strength to consider.
Another known weak point with the 2JZ is the strength of the main bearing cap or the cap that holds the crankshaft and the engine.
Rod bolts are also a big thing, so, yeah, keeping the RPM down is something that you need to definitely keep in mind.
Let's talk about those rod bolts, because I think this is an area that is a little bit of confusion and misconception.
There's a variety of different grades of rod bolts.
Obviously, in this engine, it's a stock rod bolt.
There are upgrades for stock rod bolts, and then, even if we're looking at aftermarket rods, there's a variety of different rod bolts available, different materials, different strengths.
What's important here, though, is it's not actually related to the engine power, is it in terms of what rod bolt we want?
Talk to us about that.
Yeah, so again, I've not spun one to destruction with standard rod bolts, but the general consensus is that, yeah, you really do need to just be careful of that RPM limiter, mainly because the factory components whenever really designed to go that high.
I'm not really sure how that constitutes to strength, but yeah, it's definitely a rotational thing.
Well, I mean the issue, I think, where people get confused is that the power level really doesn't affect the requirement of rod bolt strength, because power is compression, it's forcing the piston and the connecting rod down onto the crankshaft, it's the RPM.
That's really the issue with the rod bolt strength, because the rod bolt and the connecting rod itself has to slow that piston down and reverse its movement as it goes across the top dead centre on the exhaust stroke where there's no compression to actually sort of soften the piston's movement.
So that's the issue.
We've got there.
Alright, let's move into the tuning element.
So for a start, I just want to talk about what we're trying to achieve generally.
If we've got an engine with, let's say, unlimited strength, it's a unicorn when we're on the dyno and we are tuning ignition timing.
We're looking for a term referred to as MBT minimum timing for best torque, maximum brake torque timing.
What is that?
Can you give us a description?
Yeah, so that's where the engine's making the best amount of torque at the earliest RPM possible.
That's when the engine is generally under the most stress.
So with this engine we're trying to manage that amount of torque so that we're nice to those standard Conrods.
It's got a fairly small wastegate spring in there.
So with the big turbocharger we're actually able to manage that torque curve, mainly with boost control, so we don't have to really spend a lot of time chasing timing numbers and things like that.
So yeah, it's a pretty simple setup but yeah, it works well.
So just to dive a little deeper into that, when it comes to optimizing our ignition timing, what we'll generally do is start with a safe, relatively retarded ignition timing number, and we're looking at the torque numbers on the dyno and we'll creep that timing up.
And what we're trying to do is basically start the combustion event so that we achieve maximum cylinder pressure at a point in the engine cycle where we can get maximum mechanical advantage from that pressure acting down on the piston.
Maybe somewhere around maybe 14 to 18 degrees after TDC.
We've got the piston a little bit down and it's got the angulation on the connector on.
When we push down on that piston it actually rotates the crankshaft.
So that's what we're trying to achieve.
But the end result of this as well is when we're achieving that, we've got a lot of cylinder pressure correct and that can be damaging to our engine components.
Yeah for sure.
And when you're running a fuel like E85 it can sometimes be hard to find that point of MBT, because you can actually continue to put ignition timing in and the engine will take it until you come to a mechanical failure because you haven't reached the knock limit of the fuel.
So in circumstances like this you sort of have to draw from a bit of experience to know where that point you know should be.
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In terms of the tools we've got available in our tool belt to control torque you've mentioned them we've got ignition timing and we've got boost.
Either of those can affect cylinder pressure, hence engine torque and engine power.
How do you decide, as a tuner, which of those elements you're going to manipulate to get the result you want?
Yeah.
So for this specific car we've chosen to use boost control as the main sort of torque limiter.
So I mentioned before, it's got a fairly light wastegate spring in it and so we're relying pretty heavily on the closed-loop boost control to give it a nice boost curve to keep that torque fairly flat.
The ignition timing that's just sort of a known setup that I generally use with these engines.
I know that they last like that.
So yeah, the ECU has full closed-loop boost control.
We've got a few different levels in there that the driver can choose from and that sort of just changes the power level and that torque curve.
When you talk about managing the torque curve of the boost control, though, most people again would assume that we run a flat boost curve.
Let's say it's 20 psi of boost.
We get that 20 psi as early in the rev ranges we can and we just hold that flat and that sort of results in a conventional torque curve, if I can call it conventional one.
That sort of rises, peaks lower in the RPM and then as the RPM continues to climb it'll drop away again.
You're talking about creating a flat torque curve.
What will your boost curve look like in order to achieve that?
Yeah.
So being a 6870 with a fairly small rear housing, it wants to come on quite early and quite aggressively.
So we try and tame that down a little bit through the mid-range and then once we find that nice sort of peak torque number that we want to have, we'll then bring the boost in with engine RPM to hold that torque curve flat.
So you've got a boost curve, that sort of starts relatively low and then continuously.
Once you get past peak torque it will start to climb.
Yeah, correct, we're also doing a little bit of drubber wire throttle control as well, so we don't over throttle the engine down low either.
That sense of help with throttle responsiveness down low also helps you to sort of not have such a sharp spike of torque as the turbocharger comes on.
Now, so far, we've been looking at it from a perspective of engine strength and engine reliability.
Are there any advantages with this process or the way you've approached this in terms of making the car easier for the driver to actually race?
Yeah, definitely so.
It's a big engine, like I said, with a fairly small turbo, relatively speaking.
So that sort of part throttle, mid-range RPM can make the car quite hard to drive through mid-corner and that sort of stuff.
So yeah, we're trying everything that we can to sort of tame the car down.
So far we haven't talked about specific power numbers.
Can you let us know what?
it's making.
Yeah, so on the dyno it made a little over 780 at the hubs horsepower, that's on mid 20 pounds of boost, which is where I'd be comfortable with this thing to sort of live at how long it'll last at that, I'm not really sure.
John, he's gonna use those first lower boost control settings earlier on in the event, and then maybe Saturday morning we might send it full boost.
See what happens.
I'm guessing at some point there is actually a built turbo short block in the in the pipeline to suit this car a little bit more, will make it a little bit more suited to its applications, so you can actually lean on it as hard as you can.
Oh, yeah, yeah, yeah, definitely.
So yeah, he'll have a forged bottom in there that we can maybe spend to 82 or 85 or something.
It's.
The other element is what RPM is it currently running to?
We've got the limiter at 75 at the moment.
So pretty mild again in defense of those connecting rod bolts.
Yeah, yeah, yeah, definitely.
Alright, thanks for the chat much slightly different angle than what we normally go, but just important for our followers to understand that tuning is not always about just trying to achieve maximum value.
So thanks and good luck for the weekend.
Thank you, cheers.
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