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Old 06-25-2004, 07:52 AM
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Compression ratio

what do you need to figure out the compression ratio ( ie: 8:1) on an engine.
I have a rebuilt 82 Chevy 350 in my 67 GMC that has a stock bottom end, 60 cc chamber heads from a 305, stock cast intake and a 750 cfm Q jet carb. Just wondering how I can figure out the ratio on this engine. A couple guys told me because of the smaller chambered heads, I would have to run premium fuel because they create a higher compression
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Old 06-25-2004, 08:02 AM
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go to smokemup.com and use their calculator. You might have to sign up, but its no big deal-

k
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Old 06-25-2004, 08:08 AM
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COMPRESSION

Unless you have actually taken the time to measure (cc) all the parts you will be just guessing at the numbers. They are never what they are advertised at........

I used the 4.030 bore 3.48 stroke, 10 cc's for the gasket, 20,cc's for the piston volume and 60 cc's for the heads and it comes out to 9.0:1 static.

If you change the piston volume to 8 cc's the static changes to 10.3 so as you can see you wizzing into the wind kinda at guessing....

Do you have any spec's at all from the motor. What pistons, was it zero decked, do you know the cam spec's??? Thsi will help us get closer. Did you do a compression check on the motor, If so what was the psi???

Keith
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Old 06-25-2004, 08:50 AM
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I wish I would have taken more notes on measurements when building this engine, but it was my very first time rebuilding and engine. This is a stock engine out of an 82 Chevy pickup. It has a stock crank, cam shaft, rods and pistons. The head decks were shaved down by 10 thou and the heads are from a 305. I really wish I would have taken more measurements and made more notes as I tore it down and rebuilt it, but those are my rookie mistakes.
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