I'm pretty sure I'm going with the 4g64 2.1L but just wanted to make sure that it would be a better option then the 2.0L with higher compression??? My car is my DD and saw 26k last year.

 

What fuel will you be using?

 

In denver you might be able to get away with 10:1 on 93. but not 11:1 thats race gas/ E-85 area, even at your altitude.

 

We have never had any issue with 10:1 comp ratio but with 10.5:1 and above if something goes wrong it really goes wrong. For a DD i would stick with 10:1. What turbo and fuel do you plan on running?

 

I would ask other CO evo/subi owners about what comp ratio to run at your altitude. Do you have e85 there?

 

11:1 is going to be too high on anything but racegas.

If you have the same E85 we have, which is really E70, you'll have a hard time running anything over 10:1. Even 10:1 on E70 has lower boost limits in warm weather. On a T67 setup, it didn't like over about 30 PSI in the 100+ degree summer weather.

 

what you need to ask your engine builder (Dave B) is if the engine actually has 10:1 compression pistons.

Reason I say this is that most piston mfgs won't know your combustion chamber cc's (stock is 47cc, but if you unshroud the valves and match the combustion chamber to the bore size you'll have closer to 51cc-55cc's depending upon how it's done.

You also have to take into account what head gasket you're using and it's compressed thickness. That will also change your compression ratio. From what I've been informed of... the 10:1 pistons are more like 9.7:1 and your 11:1 will be more like 10.6:1

 

i wish we would have more threads about compressions and piston designs... pretty cool topics i think...

 

Along with what R/T Ernie had to say, most 10:1 pistons are just a flat top with valve reliefs. The valve reliefs are typically 4cc.

Just using a CR calculator:
85mm bore
86mm HG bore
0.047" compressed thickness
0" deck height
47cc chambers
-4cc valve reliefs

9.6:1

I've never cc'd a 4G63 head, so I have no idea how close they come to 47cc to start with. Probably not very close though considering just the amount of core shift that is typical.

Going to 50cc drops CR to 9.2 and 55cc (which seems VERY high to me) drops it to 8.7:1.

 

I would agree...55cc is very high, but I wanted to cover the spectrum!

I guess the PE headgasket is .051" and the head is ~51cc

 

I wouldn't use either one judging by your signature, actually. I'd use a 2.3 in your car with a Red. Best car I ever built was Project White, 2.3 on the Red, stock ECU, stock MAF, basically stock weight, 10.3's all day long at 138 mph on E85.

Also some interesting opinions on fuel and compression in this thread, not that I agree with them. haha

 

I'd love to hear your experience with high compression on E85.

E70 is a marked improvement over anything under 114 leaded, but I've seen how it compares to E98+unleaded fuel mixed to E85 and it doesn't...

But like I said, I have no idea if they get E70 or true E85 and it would greatly change my opinion.

Hell, maybe the E70 that we get (that is sold and claimed to be E85) is just ****? A local measured ours at around 65% to 68% ethanol.

 

what compression do you typically recommend with 93 octane on a well built (headwork, intake, good cams, etc) bigger turbo (65lb/hr+) setup at sea level?

 

Sorry 03white, not on these forums. Too many headaches, arguements and know-it-alls.

 

its too bad people ruin it for everyone. some of us really appreciate your input.