compression ratio questions

[aaronatstate]

heres my input. 8.0:1 is best. the higher comp engines always run into knock at lower power output vs octane.

With you on this one. I fully believe why I get knock sooner is because I run the 8.3:1 Wisecos, and had my heads decked. If I could do it all over again, I'd stick with 8:1.

[familyMAN]

heres my input. 8.0:1 is best. the higher comp engines always run into knock at lower power output vs octane.

Ray, what if you remove pump gas from the equation and only use race gas or ethanol? Other platforms (porsche, supra, dsms) seem to have good results with higher comp (9 to 11:1) with turbos and significant boost. What are your thoughts if you are removing octane limitation?

[AudibleSilence]

Personally, I don't want to set my car up to run on e85 or race gas only. She gets shitty gas mileage as is and those fuels are not readily available anywhere I go.. I'd rather set my car for the fuel I can get the easiest and still make awesome power.

[familyMAN]

The reason I ask, is "personally" I will be setting mine up to run on E85 all the time. It's not a DD (hell, it's not even a driver now), but it will be mostly a street car. I am strongly considering 9:1 Mahle pistons. 9:1 will be fairly mild compared to some of the builds on other platforms though.

[IPD]

that's a good read, adam. too bad it doesn't even begin to touch on forced induction. what i did learn though, was that cams effect dynamic compression ration--which is highly related to how much a turbo can feed into the chamber.

[AudibleSilence]

that's a good read, adam. too bad it doesn't even begin to touch on forced induction. what i did learn though, was that cams effect dynamic compression ration--which is highly related to how much a turbo can feed into the chamber.

Which is why I am waiting to get a turbo/blower cam

[IPD]

Which is why I am waiting to get a turbo/blower cam

i gotta ask though, since i don't recall anyone ever trying it. why not 7.5:1? 7:1? at what point does the loss of compression not yield greater HP benefit with more turbo boost? there's got to be a limit somewhere; because if there wasn't, we'd all be running 2:1 motors boosted with saturn V rocket-engine-sized blowers.

[BaadVR4]

Top Fuel dragster engines running 90% Nitromethane for fuel typically run 6.5:1 CR and around 60 psi boost. The real question is how much boost can/will I run on a "street" car. Once the upper boost limit is fixed, then the optimum CR can be determined.

i gotta ask though, since i don't recall anyone ever trying it. why not 7.5:1? 7:1? at what point does the loss of compression not yield greater HP benefit with more turbo boost? there's got to be a limit somewhere; because if there wasn't, we'd all be running 2:1 motors boosted with saturn V rocket-engine-sized blowers.

[AdamVR4]

Top Fuel dragster engines running 90% Nitromethane for fuel typically run 6.5:1 CR and around 60 psi boost. The real question is how much boost can/will I run on a "street" car. Once the upper boost limit is fixed, then the optimum CR can be determined.

And the upper limit for boost would be determined by intercooling.

That's a much easier answer than a thermo model lol

[i3igpete]

i gotta ask though, since i don't recall anyone ever trying it. why not 7.5:1? 7:1? at what point does the loss of compression not yield greater HP benefit with more turbo boost? there's got to be a limit somewhere; because if there wasn't, we'd all be running 2:1 motors boosted with saturn V rocket-engine-sized blowers.

just a matter of how big your wallet is... moving point 5 is a lot more expensive than moving point 4.