Fundamental 2JZGTE flaw?

This is meant to be a technical thread, so if you feel offended/out-of-your-depth/peckish please look away NOW

OK, now that we took care of the niceties:

As most technically-minded people here will know, an engine running 1 bar boost will (theoretically) make double the power (torque as well) of the n/a variant.

Theory gets close to reality when the CR, timing, fuelling and intercooling under 1 bar boost are all optimised.

So a well-sorted 2JZGTE running 1 bar boost should not be too far from 440bhp (two times the 2JZGE output)

This implies the turbos operating in their efficiency range, post-intercooler temps near ambient, fuelling and ignition spot on (i.e. ECU not retarding like mad)

Life isn't perfect, but a decent setup shouldn't be way off410-420bhp in real life.

But it is nowhere near that, is it?

Even in stock trim, the TT runs 10-11psi max, which is roughly 2/3 bar.

Operating parameters are pretty optimised at that level, so one would reasonably expect 220bhp + (2/3)*(220bhp) = 360+bhp, way more than the real figures.

In very rough terms, I'd expect the 2JZGTE to be making 15bhp/psi of boost, and instead it is closer to 10bhp/psi, like the 2litre 4cyl turbos.

Am I the only one to wonder why?

I'd be curious as to what the more experienced people here think.

Don't the catalytic converters come into play a lot here, too. They will increase their resitance to the flow of exhaust gasses in a non-linear way, won't they? I'd guess a fair test would be to remove cats from the equation (for both NAs and TTs).

I might be talking boswleox though!!

It's the same either comparing decated n/a-TT or catted.

This 10bhp/psi has been bugging me for a while, I just can't see why it is so low.

Every aspect of the 2JZGTE design I look at closely is very good indeed. This engine should definately be in the 15bhp/psi category, but it isn't.

Don't know a lot of this techie stuff, but Turbo engines run much lower compression than N/A's and are therfore not as efficient off-boost and therefore run less power off boost.

If the compression is say 20% less, then it could be reasonable to suggest that instead of 220 bhp for a straight 3 ltr, the TT engine off-boost may only be putting out the quivalent of 80% x 220 = 175 bhp. Double this would give 350 bhp for 1 bar boost, which is prob about right.

Probably complete bollox, though

J

Is your "twice the power at 1 bar" rule based on racing engines? or are there any real life production examples of this?

Could it be simply the cars are deliberately under tuned in trade for longevity/reliability? but then you'd expect it to be easy to simply remap and get massive gains I guess. Hmmz...

Probably complete bollox, though

 

J

it is bollox mate, as you rightly suspect, lol.

The 2JZGTE CR at 10psi boost is not far from the 2JZGE CR at full throttle (it is the effective CR that counts, and that's what mr "T" has accounted for)

Is your "twice the power at 1 bar" rule based on racing engines? or are there any real life production examples of this?

Not just racing engines, even production engines strive for efficiency.

Most 2 litre engines of recent design (1990->) are close to 10bhp/psi

A 3 litre engine of similar pedigree should be at 15bhp/psi.

The 2JZGTE is not an overblown 4 cylinder engine, so we don't expect efficiency losses due to grotesque combustion chambers or cylinder size.

It is 86x86mm, with an excellent head design.

The C20LET (opel) engine is also 86x86 with similar head design. At 1 bar held boost it produces 290bhp/290lbft, which is almost double that of it's n/a derivative (C20XE, 150bhp)

So we're talking 10bhp/psi without any fancy stuff, just optimal intercooling and sorted fuelling.

The 2JZGTE should be 15bhp/psi dammit

it is bollox mate, as you rightly suspect, lol.

 

The 2JZGTE CR at 10psi boost is not far from the 2JZGE CR at full throttle (it is the effective CR that counts, and that's what mr "T" has accounted for)

Taxi called, coat on, already left the building...

J

Taxi called, coat on, already left the building...

Relax mate, it's only the internet

The C20LET (opel) engine is also 86x86 with similar head design. At 1 bar held boost it produces 290bhp/290lbft, which is almost double that of it's n/a derivative (C20XE, 150bhp)

Is that in OEM tested and durable stock trim or home tuned trim? I thought the Opel 2.0 family 2 turbo engine (same family as fitted to the VX220 turbo) was currently more like 200bhp / 184lb/f? I don't know the stock boost pressure.

Following the logic, you could say that stock Supra running 0.75 bar of boost should more up around the 480bhp mark, since NAs only run at about 80% volumetric efficiency. So: You first have to up the NA's output to 275bhp assuming 100% VE at 0 bar boost, and then up to 175% of that (481bhp). As you quite rightly point out it is nowhere near that.

I don't think you can directly equate volumetric calcs to charge density for a turbo engine, which is what really matters for power. The real world figure will be lower because the turbo will heat up the air as it is compressed and I doubt the IC (especially the stock IC) will cool it back down to ambient (remember you cannot cool it back down to lower than ambient without using evaporative tricks like water injection or pre-compressor injection).

There is a nice diagram in the Bosch book (which I will hopefully remember to scan and post up later) that relates turbine pressure ratio and intercooler efficiency to increase in charge density. What would be really nice was a set of measurements for intake temps after the turbo and after the intercooler, to see where they lay on this chart.

John, I don't follow your thinking on the compression ratio thing. Compresison ratio = 1 + (swept vol / compressed vol). If you are implying that you can multiply the effective swept volume by the boost pressure, then you would have to apply the same factor to the compressed volume, and hence although the in cylinder pressure would be higher, the geometric compression ratio would remain unchanged. Can you elaborate?

FWIW I think the geometric compression ratio does matter. If you have an ideal situation with an NA engine running at 100% VE with a 10:1 CR and a turbo engine running ambient post-compressor temperatures, a compressor pressure ratio of 1.75 ( 10psi ish) but a CR of 8:1 then the pressure at TDC (ignoring the fact that the combustion event would have already started by then) has got to be lower than if they both ran a 10:1 CR. The final pressure in the turbo engine would be something like 1.4 x higher than the NA engine, not 1.75 times higher.

Pressure-charged engines run lower compression ratios to delay det through charge heating and high cylinder pressures. Although the maths is pretty much correct for gas throughput, I don't think you can factor up the actual power output from an NA to a turbo engine quite as simply.

The 2JZGTE should be 15bhp/psi dammit

lol, i can sense your frustration from here!!

and...relax!

My housemate has a VX220 turbo. It's got the old-skool Opel 2.0 in it, the one that comically lunches itself due to misaligned pullies straight out of the factory. And it's 200bhp out of the box, stock. Dunno where 290bhp came from, the pub perhaps? Unless that is, as Digsy says, a home modified engine in which case comparing it to the stock NA variant (which will have some differences from the turbo variant anyway) seems futile to me.

And I thought that compression ratio was just that, a mechanical ratio? Not something variable with boost pressure? If the piston compressed atmospheric pressure air by 8:1 then the input = 8 times smaller than the output. Therefore stick in air compressed to 2bar pressure, it'll still be squashed down by a factor of 8:1... Not really sure what this 'fundamental flaw' is yet, is it basically that the turbocharged engine should be linearly more poweful than an NA variant, even though the design, build, and dynamics are pretty different...?

-Ian

Is that in OEM tested and durable stock trim or home tuned trim?

Somewhere in-between. Stock it runs 10psi.

The VX220 turbo is not a good example, because it is mid-mount and has serious cooling issues

Following the logic, you could say that stock Supra running 0.75 bar of boost should more up around the 480bhp mark, since NAs only run at about 80% volumetric efficiency.

Good point, but nobody said that 1 bar boost equates to 200% volumetric efficiency.

It would be slighly less than double the n/a VE, 160% perhaps

(remember you cannot cool it back down to lower than ambient without using evaporative tricks like water injection or pre-compressor injection).

I can and I do use such methods to get full boost temps down to ambient.

Doing it on the supra currently and the SMIC is dead cold after several full-boost runs

There is a nice diagram in the Bosch book (which I will hopefully remember to scan and post up later) that relates turbine pressure ratio and intercooler efficiency to increase in charge density.

I've got it mate

John, I don't follow your thinking on the compression ratio thing. Compresison ratio = 1 + (swept vol / compressed vol).

that is the static CR, yes

Can you elaborate?

Dynamic CR mate.

At 6K rpm, not everything gets in 100%, not everything gets out 100%.

The cam timing events become a bit fuzzy with inertia, pressure ratios etc, right?

You can reduce dynamic CR without touching the static figures, just by dialling the cams. I've done it a lot in the past.

FWIW I think the geometric compression ratio does matter. ....The final pressure in the turbo engine would be something like 1.4 x higher than the NA engine, not 1.75 times higher.

yep, I agree, that's why the 'boost equivalence' CR charts you find in books are laughable. The increase is not linear at all.

I don't think you can factor up the actual power output from an NA to a turbo engine quite as simply.

well in fact you can!

You cannot extrapolate it up to 5bar boost of course, because an overstressed stock engine will be totally inefficient at that stage, making a mockery of any calculations.

But at 1 bar boost, it is very reasonable to apply this 'simple' logic, since it is very possible to keep dynamic CRs, inlet/outlet temps and ignition/timing events well within optimal ranges.

Say you've got a 300bhp Chevvy V8 which you charge at 0.5 bar, interooled and properly mapped. If you don't get another 140-150bhp, you've done something wrong.

Usually people get 130ish at that boost, because they play it safe and run it more retarded than they have to.

FWIW I think the geometric compression ratio does matter. If you have an ideal situation with an NA engine running at 100% VE with a 10:1 CR and a turbo engine running ambient post-compressor temperatures, a compressor pressure ratio of 1.75 ( 10psi ish) but a CR of 8:1 then the pressure at TDC (ignoring the fact that the combustion event would have already started by then) has got to be lower than if they both ran a 10:1 CR. The final pressure in the turbo engine would be something like 1.4 x higher than the NA engine, not 1.75 times higher.

I've just found the calc for this (on the same page as the other chart I was talking about).

Final compression pressure = manifold pressure (bar) x CR^1.35

So for the same figures above, the NA engine final pressure would be 22.39bar and the turbo engine would be 28.99bar - a factor of only 1.29 higher.

Incidentally, the 1.35 in the above equation is something called the polytropic exponent of real gases It seems to be to do with the fact that the gas is compressed so fast that it does not have time to give up its heat into it surroundings (abiabatic compression) so the actual pressure is much higher than the geometric compression ratio suggests.

I think. Thermodynamics was never my strong point

two notes here:

1. these pressures are maximums, in the case of the turbo the area under the curve is much fuller as well.

2. it is isothermic that we want, and I have managed to go some way towards it.

An engine that can make 1000bhp on stock internals has no flaws imho

maybe the thread title is not right, that's why I have the question mark.

I've been wondering for some time about this discrepancy, and now that I've configured it to hold 1 bar at almost ambient temps it looks like power is far off what it should have been (2x 2JZGE)

It is not a rhetorical question, it bugs me.

Never one to pass up on the opportunity to do a spreadsheet.

If you factor up the GE's max power by using the final pressure calc, I reckon you get something pretty close to the real figures: 362hp @ 0.75 bar boost (11psi) for a stock UK car. If you go out to 1.4 bar boost for a big single car, you get a gnat's under 500hp, which also seems realistic.

By comparison if you factor it up using boost pressure alone, the calcs turn out to be (interestingly) 25% over-optimistic accross the board.

So what are you actually getting at 1 bar boost?

...if only we had a formula to relate BMEP to final compression pressure and final compression temperature, we could work it all out from scratch and have our own little engine simulation programme. That would be neat

Factored Power.zip

Never one to pass up on the opportunity to do a spreadsheet. ..

same as me lol...

leftover from the days bygone...

Even in stock trim, the TT runs 10-11psi max, which is roughly 2/3 bar.

Operating parameters are pretty optimised at that level, so one would reasonably expect 220bhp + (2/3)*(220bhp) = 360+bhp, way more than the real figures..

...If you factor up the GE's max power by using the final pressure calc, I reckon you get something pretty close to the real figures: 362hp @ 0.75 bar boost (11psi) for a stock UK car.

Do you see a similarity in the figures above?

So what are you actually getting at 1 bar boost?

Haven't had it on a dyno yet, but it sure as hell ain't 440 throroughbreds.

(Pub orsez maybe)

Have to agree with Bobbeh, anyway theory is theory not fact (just like darwin), rules are made to be broken, sounds like your not spending enough time full throttle sideways, go have some fun mate, and give those lovely wheels i sold you some work!

Chief, when I first got the soop it felt so slow I wanted to cry.

The fact that I thought the second turbo was blown, goes to show how slow it felt to me over 4Krpm -- hey, I bought a second set of turbos days later to swap them over.

To my horror, the turbos were NOT blown, (the Dude drove the car and laughed, he said it was meant to go like this.)

Under this light, can you feel my sorrow, my pain?

I'm sure it'd 'feel' quicker if you had a manual. If you want to 'feel' fast, buy some stiffer seats

Weird one John, a fit std UK spec is a decent drive. Something tells me you are close on going big, I resisted it for as long as I could, but have given in.

Chris is right, "GO big or go home" lol You know you want to!

I'm sure it'd 'feel' quicker if you had a manual.

yes, I agree with that.

This 'auto' thing certainly gets some familiarity. Doesn't help if you're a control freak either...

Even BPU Auto Supra's I've been in dont feel particularly fast, despite getting to 120mph very quickly, its such a smooth drive its deceptive.