How much compression....
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Joined: Oct 2005
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From: Charlotte NC, behind someone going 10 under the speed limit
How much compression....
Can you get by with on an L98? I've considered going in and tweeking some things, mainly raising the compression and of course something like a 218 XFI single pattern cam ground on 113 LSA. I'd either top it with an SR or modded TPI, or the pipe dream BBK. Key is to not diminish torque, and also whatever I take away with the cam and intake mods to make up for it with compression. Heads would be ported 113's, and I'd probably go with some .030 over flat top hypereutectic (sp?) pistons to raise the comp and get the 5 cubes. Can't go 383, but willing to go inside for some mild changes.
Would this take 10.75:1? I'd mic it all assembled to select head gaskets for ideal quench. The 355 I built for my MCSS was estimated by me to be about 9.6:1 with Iron heads, .042 quench, and cranks 195-200psi on all cyls, with a Crane CompuCam 2040 210/216 114 LSA cam(built in 1997, has 60K miles now). Haven't dyno'd it but it's one helluva street car, very strong compared to the Vette, and still using a CCC Quadrajet carb and ECM system.
I've read 200 cranking is about the ragged edge for 93 pump gas. Is 10.75 reasonable? or maybe 11?
Would this take 10.75:1? I'd mic it all assembled to select head gaskets for ideal quench. The 355 I built for my MCSS was estimated by me to be about 9.6:1 with Iron heads, .042 quench, and cranks 195-200psi on all cyls, with a Crane CompuCam 2040 210/216 114 LSA cam(built in 1997, has 60K miles now). Haven't dyno'd it but it's one helluva street car, very strong compared to the Vette, and still using a CCC Quadrajet carb and ECM system.
I've read 200 cranking is about the ragged edge for 93 pump gas. Is 10.75 reasonable? or maybe 11?
Last edited by DarkBlue88; Apr 12, 2009 at 09:07 PM.
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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People go for 11:1 all the time -- without issue on pump gas. A few have gone a bit higher but usually they have big cams which lowers DCR. You probably already know this, if you don't have alum heads, that number should be lowered up to a whole point.
Last edited by GREGGPENN; Nov 2, 2009 at 11:12 PM.
Safety Car
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From: Glenbeulah Wi
You need to check your dynamic comprssion ratio to determine how much compression you can get away with. The highest dynamic compression ratio you can (safety) use with 93 octane pump gas is 8.5 to 1, and then you need to have the engine built correctly. Your write-up indicates that you know how to build the engine correctly so you need to pick the cam that suits your power band and then pick the static comprsion ratio after you check the dynamic compresion ratio. If you are planning to run near the 8.5 to 1 dynamic compression ratio you must also keep the engine cool otherwise it will detonate.
