[mhooper2]

I was wondering if anyone has done back to back test changing only the compression on the 2JZ. (Doubtful but figured I would ask anyways)

With stock compression being 8.5:1 utilizing a larger turbo seems to me that increasing compression to 10:1 would increase efficiency and move the curve to the left ( thinking ~300-400 RPM on a 74MM).

E85 loves compression , however what (if any) would be the benefits for race/pump fuel?
Downsides?

Thoughts?


Edit- I enjoy these discussions=)

 

[93targasupra]

I only run on E85 now and nothing else. I was going to raise the CR but was told that boost beats compression every time. I guess if your looking for the down low power and running less boost it would be good (like you said, moving the curve to the left). I am also interested to see of anyone has any testing done on this.

 

[MetalGearMotorsports]

Alpha and Errol are the ones to ask, they have knowledge about higher compression ratio's with E85. but it is not just limited to E85, alot of race gas guys have stepped up to 9:5.1 - 10:1 on boosted applications with awesome results. its all in the tuning

 

[Vlads2jz]

Each fuel has to be compressed a certain amount to ignite and to burn its best. Diesel for example needs very high compression. Gasoline has a certain compression it likes most and E85 likes to be compressed a bit more then gasoline to work its best. That is why its smarter to run higher compression on E85 besides its resistance to knock. I know alpha and errol will both recommend to run higher comp on e85 setups as they have seen gains in doing so.

 

[Seattle Express]

From what I understand, you're asking what the benifit would be to increase the compression ratio while using pump or race gas. With pump gas I don't see much improvement, in fact it wouldn't be good in my opinion because your boost and timing would be blocked by the octane. So unless your planning on doing most your aggressive driving with a higher octane fuel, I think increasing compression is a loss, because you have to dial down your boost too, so any miniscule gains in low end torque will be totally eclipsed by the massive drop in high end power. If you ARE running a higher octane fuel, then increasing compression would definitely be benificial. The higher octane overcomes detonation caused by the increased compression. Look at stock GE's for example. I don't think they can run more than 9 or 10psi on pump which makes them put down around 350-370whp. Their increased low end torque over the GTE's doesn't do as much for performance as the extra 8 or 9psi a GTE can boost on pump.

Bottom Line:
If you're octane limited-------> Lower compression
If NOT octane limited----------> Higher compression

 

[Bugermass]

We regularily run higher compression on boosted setups (non-supra) I am totally for it.

 

[Captain Bondo]

Each fuel has to be compressed a certain amount to ignite and to burn its best. Diesel for example needs very high compression. Gasoline has a certain compression it likes most and E85 likes to be compressed a bit more then gasoline to work its best. That is why its smarter to run higher compression on E85 besides its resistance to knock. I know alpha and errol will both recommend to run higher comp on e85 setups as they have seen gains in doing so.

Diesel engines need high compression because diesel engines rely on compression ignition, not spark ignition. Totally different thing bud.

I agree with Seattle Express, it's simply to do with the detonation threshold of a given setup on a given fuel.

On supra motors you maybe can't quite take it quite to the same extreme as you typically can with smaller bore motors (IE 81mm Honda engines with the small bore and very compact fast burning chambers are very det resistant so the limit in terms of useable compression ratio vs. fuel octane on boosted motors is a little higher), but that said we've all seen just how well NA+T motors have worked when built by folks who know what they're doing.

 

[Beau]

Basically the more combustion chamber volume the greater propensity for multiple ignition points, however there are some good designed heads out there that limit detonation despite volume.

 

[Riceater]

Higher compression motors need to be ran on either race gas or E85.. otherwise the boost will have to be turned down so low to make it safe that you're only hurting yourself.. thus destroying streetability which I imagine you'd like to keep since you drive a Supra lol.

In my Evo, the advantages of switching to a 10:1 compression were amazing. I didn't really notice much of a spool difference but you get into your power band quicker since you're making more torque out of boost and a little more horsepower (within the turbo's efficiency of course). Just look at some of the shop built cars.. I'll almost guarantee that most of them that are in the 8s or faster are running at the very least higher compression so obviously it's worth doing if you're after maxing out your setup. I read a while back that for every point of compression increased there's an average of a 10% power increase.. now I'm not sure if this applies to 6cyls but I'm sure it's fairly close.

So to put it plainly, if you're already running a car on E85 or race gas.. go for it! But if you're a pump gas guy and don't care to switch or it's just not available in your area then don't even think about it, not worth the hassle.

 

[Brian Robards]

We run 11:1 compression in our red car and it seems to really like the extra compression. Originally we were running methanol but have since switched to Q16 for fuel. We ran this setup last year with a 76mm turbo and were going consistent 8.5s at 167 on boost at 3150lbs.

 

[suprajens]

how much boost are you running ?

 

[Brian Robards]

33psi. We will probably be running 35 - 38 with the 88mm

 

[m_life]

There are 2 cars i know of running 9:5.1 CR, one with HKS twins and one with a GT74 running 700+ with zero det and those are both running 99 octane.

 

[Seattle Express]

Higher compression can simply NOT be taken advantage of on OUR cars (2jzgte) with out the a higher octane fuel or a denser cooler buring fuel like ethanol. It's THAT simple. Bumping the compression up to say 10:1 or 11:1 on a supra that will see pump gas 99% of the time is just stupid in my opinion. Do you want to drive around all the time blocked at 370whp??
A TRACK supra, on the other hand, that sees nothing but exotic fuels or ethanol would take major advantage of the higher compression.

 

[rotortuner]

One of the reasons why boost beats compression is because when you run higher pressure from the turbo, that air being compressed heats up (pv=rt), you can then cool that air with the intercooler making it more dense. if your gaining more pressure by compression only, that air is heated in the cyl and is not cooled, therefore the air is less dense and NOT as efficient as compressing it with the turbo and cooling it in the intercooler. MORE BOOST!

CJG

 

[D'Bollocks]

^^rotortuner.....that doesnt make sense

 

[suprareyrey]

I run 9.5CR at 38 psi of boost on E-85 Like a champ

 

[GTR-Racer]

^^rotortuner.....that doesnt make sense

The atoms are more compact (less space between them) at lower temperatures.

 

[Craig Bush]

^^^think you mean 'molecules', not 'atoms'.


craig

 

[GTR-Racer]

^^^think you mean 'molecules', not 'atoms'.


craig

Just explaining the basic theory, in this case it's oxygen molecules.