Higher compression has advantages you may be missing. Higher compression motors emty the chamber better. Making the following intake charge less contaminated. The smaller chamber is also easier to fill. This becomes increasingly important as higher hp cars turn to higher rpm for power where it becomes harder to fill the chamber because there is less time to do it. Engines are less likely to detonate at high rpms because the flame front moves so fast it doesn't give time for detonation to take place. Higher compression motors use less timing advance. There are less pumping losses. And lastly air coming out of the turbo is hotter at higher boost pressures. But on to some practical examples.

Slowboy recently tested a bunch of different turbos on the same motor. They started the testing with a 10/1 compression block. They tested a couple of turbos. Then they got quite a few complaints from people saying that most people would be using the turbos on lower compression setups. So they ditched the 10/1 block for a 8.3/1 compression shortblock. Then they started the turbo testing again.

57 trim turbo with 10/1
15psi 345/309
20psi401/378
27psi 459/???
57trim with 8.3/1
15psi 290/245
20psi 325/320
25psi 361/361

Reported spool difference between the two compressions was 200rpm faster with the 10/1 block.

before John Sheppard switched to alky he ran 11/1 2.0 at 56psi boost. Don't know what compression he switched to for alky but he sold off his spare 11/1 pistons at the time of the swap to alky. Local race team here in tampa has a supra motor running 14/1 on alky. A friend of mine helps out with the car and says he has seen them make passes as high as 71psi boost.

The reasons people have better results with more reasonable compression 8.5-9.0 is because it is easier to map the timing. Especially when the factory maps are based off 8.8/1. Mapping a high compression turbo engine is not easy. But the rewards are there. Porshes turbo 911 has been 9.4/1 from the factory for a few years now.

 

Enough power such that when the power curve is plugged into a shift point calculator, the resulting acceleration curves are at least as strong as the previous setup. To make it simple however, I'd say 4.11 gearing is a worthwhile option for anyone who has a 2.3L setup and enough power to reach the end of 4th before the end of the 1/4 mile (assuming that is important to him).

One thing to consider about this swap is your speedo will likely be reading too low by 10%, so one might want to check to the availability of a speedo gear (?) that compensates for the difference in the final drive gearing.

 

Reporting only 361 whp on a Dynapack with a 57 trim @ 25 psi seems especially weak to me, so I would need to see data of better, more convincing quality and detail to consider said test at face value. I appreciate your posting that nonetheless.


Mapping and running a race engine on the ragged edge of destruction for 8-9 second race makes for interesting reading, but isn't a methodology that should be considered viable for street applications. Likewise, I believe pure alcohol to be far more forgiving in this regard than gasoline. This is another instance where what happens at the race track isn't suitable for the street, despite romantic notions to the contrary that so often happen here.

I agree completely that assuming competent piston/head design and tuning, a higher compression engine improves evacuation and spool characteristics, but there are tradeoffs, and hence the reason why turbo street engines are most often designed around 8-9:1 CR. As for Porsche, the 9.4:1 CR of that turbo 911 is probably intended to improve spool characteristics with a turbo large enough to produce considerable power (although its power curve shows that it does only very briefly), and it does not appear to offer anywhere near the potential to run a boost pressure of 30-35 psi that has proven possible over the long term with 8.5-8.8:1 EVOs. In fact, that turbo Porsche runs only 1 bar (~15psi), and does so for just a few hundred rpm.

 

guys thanks a lot i was going to get a 2.3 stroker but ive decided that Im going with the 2.1L Destroker so i can rev to 10k rpm to get the most outta the powerband...

 

wow I didnt know a 2.1 can rev up to 10k safely.

 

!!!A 2.1L is a 4G64 block with 4G63 Crank,Long Rod,Overbore piston.That what Curt Brown use to run 10.5@127MPH on stock turbo and 600whp(BR nightmare dyno) on GT35R(No nitrous).He will hit the track tommorow.

 

Don't bet on it!

Revving any configuration to 10k rpm is a great way to break parts in such a manner that repair requires at least a new crankshaft and/or block, much less replacement rod(s) and piston(s), as one forum member recently discovered after a few trips to 10k rpm with a built shortblock.

Want to rev it to 10k? Be prepared to rebuild/replace it during or after a season of racing. Want to drive it daily on the street? Forget 10k rpm.

 

I'd guess 8500 RPM limit for a daily driven 2.1L would be good enough?

 

That should be sufficient for any GT35R application, and is a much safer limit than 10k rpm. There is NO reason to rev even a 2.0L to 10k rpm unless one has a turbo larger than a GT35R and a power curve to support it.

Those who dream of revving to 10k rpm for no justifiable reason other than the fact that they think it's cool just end up fulfilling the age old adage about a fool and his money . . .

 

yea i wasnt saying actually reving to 10k just up in the 8k's would be awesome...
who has good deals on 2.1l destrokers????

 

holy crap!!! 10.5 on the stock turbo?!?!?!? was he sprayin???

 

No spraying.He dynoed 400whp on BR Night mare Dyno (-490whp on Dynojet number).The main mod is.....driver and mod combination.

 

Yea curt brown is a f'ing hoss.

 

wow, 10.2 on stock... Why cant i get that lucky

 

10.5