Fundamental 2JZGTE flaw?

[JohnA]

i'm still a bit unsure of why you expect 15bhp/psi. is it because of the extra 50% capacity over the 2litre (10hp/psi + 50% = 15hp/psi)?.

basically yes

.

Can you explain your logic here?

Cheers.

search for 'grotesque' in the first page of this thread mate.

[Digsy]

But at the risk of going around in a circle again, the only justification for the 10/psi figure seems to be John's experience with the Vauxhall 2 litre, but that only makes 5hp per psi in stock trim (apparently because of poor intercooling), and (with John's FMIC fitted) 8.8hp per psi

 

So that's 2.5hp per psi.litre (stock) and 4.4hp per psi.litre (modded)

 

By comparison the Supra makes 9.6hp per psi, or 3.2hp per psi.litre (stock).

 

John is expecting to see 5hp per psi.litre, but so far none of the examples given have actually achieved that.

 

Before we go searching for a problem that actually may not even exist, I'd like to see more justification for this 5hp per psi.litre target figure.

[Ian C]

Now that's a summation

 

7 pages to find out it's a non-argument lol

 

-Ian

[JohnA]

But at the risk of going around in a circle again, the only justification for the 10/psi figure seems to be John's experience with the Vauxhall 2 litre,

It is standard practice, as I keep repeating time and again.

 

This I had first experimentally confirmed when I was into turbo bikes, the vaux 2 litre reconfirmed that it also works for car engines too (bigger cylinders)

The vaux engine is just an example because I had it recently 'trimmed' to shape. It's nothing special.

but that only makes 5hp per psi in stock trim (apparently because of poor intercooling), and (with John's FMIC fitted) 8.8hp per psi

Yes, and with everything else in place it pretty much did 300bhp at 1.0-1.1bar held, which is 10bhp/psi

 

The supra has no obvious flaws that send it away from the theoretical ideal, not at the stock 10psi boost.

 

That's why I am wondering why they didn't get 150bhp out of that boost pressure. It should have.

[chilli]

At the risk of being really dumb here (so excuse my ignorance) even with the reduced CR of the GTE engine you are still burning more fuel in the same space (at one bar potentially twice as much, but does all of it get time to burn fully - well that’s another issue)- and this creates more heat, heat = lost energy...

 

Where in the simple 1bar = twice the power is this taken account of? Sorry if I've missed the obvious, mechanical engineering/thermodynamics is not my specialist subject but I'd like to know how this is accounted for.

[eyefi]

**more posts happend between hitting reply and actually sending the reply. i'll leave the post here though**

 

yeah, ive already read the thread and it just doesn't convince me that your expectations are realistic.

 

are you saying that a for a blown 1ltr engine you would expect 5hp/psi and for a 6ltr engine you would expect 30hp/psi, a 12ltr 60hp/psi? i don't think it's quite as simple as that.

 

i've never known anyone expect double the power (under the conditions you mention) from a turbo engine compared to the na.

 

can you name any other 3ltr blown engines that produce 15bhp/psi?

[JohnA]

... even with the reduced CR of the GTE engine you are still burning more fuel in the same space

more accurately, you are burning more air & more fuel in a slightly larger space (CR reduction)

Under operating conditions the aim is for the 'effective' CR at full boost to be similar to that of the n/a version at full throttle. (at max torque revs, if we want to dig deeper)

The extra amount of mixture burnt pushes the piston down harder and for longer, hence the increase in engine torque.

That is whole idea behind forced induction.

(at one bar potentially twice as much, but does all of it get time to burn fully - well that’s another issue)- and this creates more heat, heat = lost energy...

That is why you need to 'readjust' several parameters when turbocharging (properly) a n/a engine.

Good OEM designs (like that of the supra) do this pretty well --- for std boost pressures.

As you increase boost yourself, the parameters start veering off the optimal, hence the diminishing returns hitting hard and fast (a stock engine running at 1.5bar will make nowhere near the theoretical maximum, predicted by the new pressure ratio)

[Digsy]

I'm not following this 5hp per psi.litre standard target at all.

 

The 2JZ and the Vauxhall 2 litre are engines of a similar vintage, both 86x86 square, both iron blocks and ali heads, both pent-roof combustion chambers, both 4 valve, DOHC, both direct acting tappets, both running 10 / 11 psi boost. They are similar engines. In stock form they both produce similar hp per psi.litre numbers.

 

If you want to look at a more contemporary engine, GM's latest 2.0 litre NA and turbo engines produce 140 and 175 hp respectively at about 5.8 psi boost. - that's 3 hp per psi.litre still under what the Supra managed almost ten years before it.

[JohnA]

yeah, ive already read the thread and it just doesn't convince me that your expectations are realistic.

....i've never known anyone expect double the power (under the conditions you mention) from a turbo engine compared to the na....

 

Maybe I wasn't clear enough, I'll try elaborating further (trying to keep the tech level reasonably low, it does mean risking some people finding it paedantic, and others boringly incomprehensible )

 

There is no such thing as 'absolute' bhp/psi for all engines.

 

Take 3 litre 6cyl engines for example. One will make 150bhp in n/a form (old 2valve/cyl design), another will make 220bhp (new pentroof etc).

 

Suppose now that we 'ideally' turbo/supercharge both of them at 1 bar boost.

The 'old' one will be expected to roughly make an extra 150bhp, the 'new' one an extra 220bhp.

This exta power comes from operating at 15 (say) psi boost pressures.

So the 'old' one gains 150bhp/15psi = 10bhp/psi

The 'new' one gains 220bhp/15psi =~ 15bhp/psi

 

Life isn't ideal and theoretical figures cannot be achieved, but with good intercooling, decent manifolds, proper pistons and decent mapping it is fair to expect that sort of gains at 1.1bar, trust me.

 

My expectations for 15bhp/psi when it comes to the 2JZGTE came from the n/a performance of the GE, combined with the attention to detail Toyota appears to have spent on this design.

The 50% increase over a 2litre's 10bhp/psi (15 vs 10bhp/psi) came from my own comparison to the Vaux 2lt engine which I've happened to be intimate with recently, and had it at some point 'optimised' for 1 bar operation, close to theoretical perfection. And indeed it made double the power of the n/a version (2 x 150bhp) at 1.1bar.

 

I regard this comparison to the 2JZGTE as relevant, because that engine (C20LET) is practically 2/3 of the supra engine. It has 2/3 of cylinders, each cylinder has identical dimensions, and the head/valve design is very similar. They come from similar design 'age' and it's no surprise that the n/a versions make similar bhp/litre.

 

Now if that engine can produce roughly an extra 10bhp/psi (up to 1 bar, while the 'parameters' are fairly optimised)

 

....I think it is fair to expect an extra 15bhp/psi from the 2JZGE engine running similar boost.

 

That is where the psi/boost came, it is not an absolute figure. I thought it was made clear from my first post, but no problem, I now hope that it is clearer.

[JohnA]

...The 2JZ and the Vauxhall 2 litre are engines of a similar vintage, both 86x86 square, both iron blocks and ali heads, both pent-roof combustion chambers, both 4 valve, DOHC, both direct acting tappets, both running 10 / 11 psi boost. They are similar engines. ....

precisely

(Ok, the vaux has hydraulic tappets, but for this comparison this is irrelevant)

[chilli]

more accurately, you are burning more air & more fuel in a slightly larger space (CR reduction)

 

Yes ok it's a slightly larger volume obviously because the CR is lower, in terms of heat generation (and the dissapation of this heat) isn't it effectively the same? i.e. much more heat with no better way to get rid of it from the chambers...

[chilli]

Ok, I've thought about this some more, how about thinking of it in a totally practical sense (since that's where the question was originally aimed):

 

Take the N/A engine, add all the pipe work, turbos (and get them doing the work of compressing) but don't connect the pressure into the engine intake. Now measure its actual BHP as an N/A but with losses of a turbo’d system (it will now be less). Now that is the figure that "in theory" you might be able to double at 1bar, but even then losses such as the ones above such as heat still mean you won't get 100%, but at least you will be starting from the right point.

 

Does that perspective help anyone?

[JohnA]

Does that perspective help anyone?

Chilli, you are right in thinking that the turbocharger is a restriction in the exhaust, however this is a very basic concept that is not really relevant here. Turbocharging a n/a engine (properly) does not simply involve slapping a turbo manifold. Other changes are done as well, cam timing and phasing being in the mix.

It is a new balance we try to achieve on-boost.

The turbocharger is also a restriction in the intake, that's why turbocharged cars with blown turbos are much slower than the n/a versions (plus the static CR is lower, cams are milder, ignition is less advanced, and more)

 

This is one of the reasons that you cannot reach the theoretical 'doubling' at 1 bar boost. Normally you need about 1.1bar to double.

[chilli]

Personally I'm sure it's the sum total of all the losses mentioned that add up to the missing bhp you speak of. I don't think you are going to find some missing piece that single handily explains it.

 

Regarding the temp losses:

 

If PV = nRT, then if the temps rise in the combustion chamber because more energy is being dissipated in a similar (effectively the same) space then V is fixed, P is fixed, what gives? The Charge density must go down mustn’t it, so you lose efficiency...

[paul_k]

Dont forget Enthalpy and entropy can have an affect...

[JohnA]

Yes, lol....

[Digsy]

more accurately, you are burning more air & more fuel in a slightly larger space (CR reduction)

Under operating conditions the aim is for the 'effective' CR at full boost to be similar to that of the n/a version at full throttle. (at max torque revs, if we want to dig deeper)

 

John, quick question: What do you mean by "effective CR"? Its the second time it has come up in this thread and I can kind of see what you are getting at, but I'd be interested in seeing how it is derived.

 

If you mean final compression pressure, then at max boost the GTE (even with its reduced geometric CR) has a much higher final compression pressure than the GE at max torque: About 21.5bar for the GE (assuming 90% VE) versus 31.5bar for the GTE (assuming 0.75 bar boost).

[JohnA]

John, quick question: What do you mean by "effective CR"?

It is based on the static CR, varies with VE and boost and has to be adjusted for cam timing.

It is a reflection of what is left in the combustion chamber under those conditions once the piston is at TDC.

 

Do you remember when in n/a tuning high-comp pistons always had to be augmented by 'wilder' cams? Well, keeping the effective CR unchanged at full torque was the main reason -- or else *bang* under the same octane fuel.

(Piston giveth, cam taketh away)

[chilli]

yeah I was wondering that also. It's clear that the overall compression on the gte is much higher than the ge, but isn't it always for a turbo vs an n/a? I've never seen a standard production turbo engine with the CR reduced so much as to match an N/A equivalent on overall "effective" compression. Does anyone know of one?

[JohnA]

yeah I was wondering that also. It's clear that the overall compression on the gte is much higher than the ge,

it is slightly higher during stock boost operation

[chilli]

Well see for me, that’s interesting. The whole doubling of power at 1 bar thing would mean you can charge the cylinder and burn literally twice as much (everything else being perfect - which it isn't anyway).

 

Now if the dynamic running compression of the GTE under full boost is only "slightly higher during stock boost operation" than the GE and we see that the CR has only been dropped from 10 (GTE) to 8.5 (GE), that indicates to me that no where near twice as much charge entering the cylinder at 1 bar (which also doesn't really surprise me).

 

So with less than twice the charge to burn, why would you hope to make twice the power?

 

That’s a lay person’s view point to some extent, but I don't think you need to overlook the obvious and try to find some esoteric reason to explain such a "big" discrepancy between the "actual" and what was purely supposed by your original question - that started this whole thread.

[Digsy]

It is based on the static CR, varies with VE and boost and has to be adjusted for cam timing.

It is a reflection of what is left in the combustion chamber under those conditions once the piston is at TDC.

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.

 

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

[chilli]

Or has anyone got dynamic compression presure readings for the GE (full throttle) and GTE (full throttle and boost), that might be interesting!

[Digsy]

Or has anyone got dynamic compression presure readings for the GE (full throttle) and GTE (full throttle and boost), that might be interesting!

If anyone has any in-cylinder pressure readings for the 2JZ I'd be gobsmacked. I suppose someone, somewhere might have done it, though.

[chilli]

well me too, but I'm presuming Mr T did it and wondering if the figures ever made it to the public domain...