Fundamental 2JZGTE flaw?

[Digsy]

Has anyone got those cam timings for the GE and GTE?

Found them on the NZ site

[chilli]

wow post them or a link, it might well be quite revealing!

[Digsy]

Cam timings and a load of other base engine stuff is here

 

Yeah, Toyota will have done in-cylinder traces. Would be interesting info to see, but not sure how much use it would be to the average tuner.

[JohnA]

Ok, yeah, I get it. That's pretty much the same as using the final compression calc but replacing the geometric CR with a CR figure calculated from the compression height at the intake valve closing point, rather than at BDC.

pretty much.

In good models it varies with revs, lobe height (and profile), and pressure ratio (for overlap adjustment)

[chilli]

I wonder, at 0.8 bar stock, the supra was designed with two small turbos (and a sequential system) for minimal lag. These would have been picked on the usual criteria of "pick the smallest turbo that can cope" for the desired bhp/flow and I'm assuming they chose the bhp's we ended up with by design as a trade off against the other factors mentioned before, not due to a flaw or issue with the engine itself. The turbo sizing is fairly self evident as anyone who wants to seriously tune the car soon realises.

 

Has anyone put a larger turbo (that would give more lag but less exhaust backpressure) in and run it at around the .08 or 1 bar (rather than the usual loads of boost). I'm wondering if you can get a bit closer to the ideal if you don't mind trading lag for bhp and using a bigger turbo that offers less backpressure load on the exhaust of the engine, along with a free flowing exhaust system etc. Don't forget just a de-cat (and cat back) can raise the efficiency a little, all these little losses add up.

 

With a laggy but larger turbo and a free flowing exhaust, I wonder if that regains some of the power that appears to have gone astray and you get closer to the ideal.

[JohnA]

I wonder, at 0.8 bar stock, the supra was designed with two small turbos (and a sequential system) for minimal lag. .

low boost threshold more likely

[chilli]

well most likely both don't you think, no good having a low boost threshold and loads of lag...

[Guest kingsley]

Hi all,

 

There is lots of interesting information on this thread but I can't help feeling that everyone seems to be missing John's rather simple point. I've rambled on a bit here so please bear with me.

 

John is saying that, with simple optimisation for the boost pressure in question, at 15psi of boost you would expect an engine to produce almost twice the power output of its NA stablemate. By simple optimisation, he means that the charge temps are decent and fuelling and ignition curves are close to optimal (that's what I think he means anyway).

 

I gather that this isn't something he's just made up but something that he's seen as a fairly normal result from what he's seen/read from experiences of various tuners, and is also borne out by his own experiences with his Calibra.

 

John's Calibra had a large (for a Calibra) FMIC to sort out the charge temps. His Supra also has got well sorted charge temps because he's got pre-compressor injection and his charge temps are no higher than ambient. While you could argue that his Calibra was more modded than his Supra, this actually levels the playing field because the intercooling on the stock Calibra is so rubbish it would not be a realistic comparison. He's done the required modifications to each to bring the charge temps down to reasonable levels and so the comparison is good and valid.

 

As has been mentioned earlier on this thread, the NA version of John's Calibra engine (the C20XE) in stock form develops a peak of 150bhp. You would therefore expect two of them together to make 300bhp ... and 1.5 of them to make 225bhp. The NA Mk4 Supra engine is remarkably simimar to 1.5 of the C20XE - both 86x86mm, similar shaped head, etc and the power outputs per cylinder are comparable (ie about 37bhp each).

 

So why does the same comparison not apply to the turbos? Same boost, very similar charge temps, same cylinder dimensions, yet the Supra TT's power per cylinder is way down on the Calibra T with what appear to be near-identical parameters.

 

[the stock Calibra Turbo makes 50bhp per 500cc cylinder with a rubbish intercooler and about 0.6/0.7 bar and correspondingly high charge temps so why does the Supra TT only make similar amounts with a far better intercooler and 0.8 bar?]

 

You can have complex discussions about volumetric efficiency etc until the cows come home but at first glance the same argument ought to apply to both engines ... yet it doesn't seem to affect the Calibra.

 

Clearly there are some differences else the power outputs per 500cc cylinder of the Supra TT really would be very similar to the Calibra T in this case. It is these differences that John is trying to find.

 

Areas that I would be inclined to look at are:

 

• exhaust manifold pressure - does the complexity of the plumbing in the sequential system plus whatever is in the rest of the exhaust system add up to being a more restrictive exhaust system than was on the Calibra?
  
• cam profiles - are the Calibra T's cam profiles more similar to the C20XE's than the Supra TT's are to those of the NA Supra? (ie have Toyota made more changes to their turbo cams than Vauxhall did?)
  
• fuelling - an over rich mixture is super safe but can dampen power output
  
• ignition timing - the Calibra had a clever auto-advance knock sensing system that kept timing optimal - is the Supra's timing too retarded?
  
• compression ratio - the Calibra is 9.0:1 (I think) yet the Supra is 8.5:1. Down the pub everyone would say that 9.0:1 is better but in a turbo environment the lower CR of the Supra may actually be more condusive to higher power output as it allows more advanced ignition timing ... so the mystery deepens even further because maybe the Supra should be producing more power per 500cc cylinder than that Calibra partly because of this, not less.
  

 

I suspect the problem may be a combination of at least some of the above factors and possibly a few others I've not thought of. Due to the amount of the discrepency of per-cylinder outputs between the Calibra and the Supra, I would expect that more than one of the above is at play here.

 

Comments welcome. Um, or expected. Encouraged. Whatever

[JohnA]

...[*]exhaust manifold pressure - does the complexity of the plumbing in the sequential system plus whatever is in the rest of the exhaust system add up to being a more restrictive exhaust system than was on the Calibra?

broadly speaking, yes. The turbos are relatively small and tight, below 4Krpm all gases are routed to just the first one, so exh backpressure is particularly high most of the time.

cam profiles - are the Calibra T's cam profiles more similar to the C20XE's than the Supra TT's are to those of the NA Supra? (ie have Toyota made more changes to their turbo cams than Vauxhall did?)

For starters, the supraTT cams have practically no overlap, to compensate for the abnormally high exh/intake pressure ratio during most of the rev range

 

fuelling - an over rich mixture is super safe but can dampen power output

This I am optimising currently. Different supra ECUs have different patterns (in the States they swap early ECUs with late ones to avoid a lean zone we haven't even got in the UK)

In general supraTTs run rich as hell under high load.

 

ignition timing - the Calibra had a clever auto-advance knock sensing system that kept timing optimal - is the Supra's timing too retarded?

no, it is more advanced

Empirical evidence shows that the range of movement is more extended too. (it can take advantage of high-octane fuel and retard quicker and further, compared to the Motronic)

No decent datalogging though, so can't say how much

 

compression ratio - the Calibra is 9.0:1 (I think) yet the Supra is 8.5:1. Down the pub everyone would say that 9.0:1 is better but in a turbo environment the lower CR of the Supra may actually be more condusive to higher power output as it allows more advanced ignition timing ... so the mystery deepens even further because maybe the Supra should be producing more power per 500cc cylinder than that Calibra partly because of this, not less.

Indeed, at 1 bar boost the supra should be better optimised overall. It also has the 'swirl' action on the intake, FWIW under boost.

 

 

PS

 

Kingsley is from the skyline camp, but don't hold this against him, lol...

I did not ask him to contribute here, but it's all the better that he did, doesn't hurt.

 

I'll revisit this thread after I've brought my AFRs down to human levels and done a few RR runs at 1.1 - 1.15 bar.

I won't rest until it does at least 450 horses at this boost level. (horses of the 'flywheel' variety, basically double the n/a figures)

[Digsy]

Welcome to the board Kingsley.

 

While the thread has wandered about a bit, I don't think eveyone has missed the point entirely. However, as you can see I think its been talked to death.

 

As I've said before, in stock form the 2JZ makes more bhp/psi.litre than the C20. John apparantley had / has a C20 with near ambient intake temps which made more. AFAIK he does not actually have pre-compressor injection on his Supra. We've done what may or may not happen when the Supra's charge temps come down to death.

 

I can't see any point in further critiquing the 2JZ based on the data available. The only way this is going to move forward is for someone to post up a powercurve, an AFR trace and an intake temp trace for a suitable BPU Supra with low intake temps.

 

[JohnA]

bit more info on the subject.

A 'mild' BPU supra -UKSpec (around 1.1bar at max power rpms) runs from the factory an AFR=10:1 which is well on the rich side.

Leaning this down to low 12s produced a mild increase in torque and 5% increase in max power. Not exactly earth-shattering material.

 

So the bulk of the missing horsepower is still at large. The 'safety richness' accounts for a modest drop in power, nothing to lose sleep about though.

 

The efficiency of the turbos is now under the microscope, I saw some pretty strong power increases while injecting before the compressors, which became more dramatic as the boost injection point was lowered down to 8psi. That's supposed to be well inside the efficient island, so there should be no gains (even mild losses perhaps) yet it jumped 15bhp just from lowering the activation point. And we're talking boost pressures of only 1-1.1 bar.

 

I'll get to the bottom of this eventually, I suspect that the stock turbos can be pushed far harder than people think...

[chilli]

I'll get to the bottom of this eventually, I suspect that the stock turbos can be pushed far harder than people think...

 

When you say this, I presume you mean "more bhp from stock turbos within the same safe pressure limits" not "we can get more pressure out of them in order to get more BHP"? Just checking because thats not really pushing them far harder is it?

 

It would be great if you can uncover some way to do this of course

[JohnA]

When you say this, I presume you mean "more bhp from stock turbos within the same safe pressure limits"

yes of course, if one can speak of 'safe limits' while operating outside the manufacturer's range

 

It would be great if you can uncover some way to do this of course

It's precompressor injection, I've said it before.

Same pressure ratio, higher output air mass, lower output temps (hence no need for FMIC), lower need for higher-octane too.

There's always a catch of course, I wouldn't want to describe anything in detail until it's proven to be safe.

[chilli]

Well it's all good stuff, this thread has been an intriguing one in general. Keep us posted with what you find, I for one am very interested.

 

Whilst I do agree that the standard set up could be considered down on power a little (but then it was primarily designed for a jap market originally with its particular constraints/requirements), I think people have shown that a simple BPU car can start to realise the power levels you would expect, given what is there to work with in the first place.

 

For example, approaching 475fwhp at 1.2 bar (using standard turbos) as members here have, shows that the engine itself is capable of roughly what you would expect - given the right conditions... and that’s with turbos pushed right to the limits, beyond their peak efficiency range.

 

If you can find a way to achieve this (or more) at lower pressures then thats great, still not sure that means the original set up is that far off the mark though.

 

As a slight aside, have you considered a CW SMIC John? I'm thinking of this now as an upgrade rather than the obligatory FMIC (which I am less convinced by at the moment).

[JohnA]

Whilst I do agree that the standard set up could be considered down on power a little

A lot

 

For example, approaching 475fwhp at 1.2 bar (using standard turbos) as members here have,

I'm not too sure about this, I only believe before/after measurements when they've been done in the same way.

 

Hypothetical example, pure fiction: someone goes into a RR and they measure 300hp at the wheels, then pump that up to 440 'flywheel' claptrap (30% losses, plus it's an auto, plus it's hot etc etc)

Then the punter assumes that the car in stock form would produce 320hp (flywheel or whatever) on that same RR, so hey-presto, he got another 120 thoroughbreds. Yee-blody-Ha.

 

If a RR (or hub dyno) shows a stock supra to be producing 320bhp (or thereabouts) then shows this 1.2bar boosted example producing 475 of the same kind of horses, then this whole thread is a waste of cyberspace, electron torture and timewasting...

I'd be proven wrong in starting the thread in the first place.

 

As a slight aside, have you considered a CW SMIC John?

yes I did consider buying one, but I was lucky enough to find a stock SMIC in excellent condition for £50.

My plans have always involved low turbo-discharge temps, so the new-ish SMIC was the best option for me.