Thread: Compression

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What cam are you running? Have you checked the DCR (dynamic compression ratio) which gives you a more accurate picture of your engine's compression that static compression ratio? You can go to the Keith Black website and use their calculator. You will have to know your cam specs, your head gasket specs, combustion chamber size, pistons relief in cc's, etc. For use with pump gas, you ususally figure a maximum DCR of 8:1 for iron heads and 8.5 for aluminum heads. My static compression is 10.6:1 but with the cam I chose, I have a DCR of 8.46:1. I have no problems running 93 octane. To run less octane, you need to lower the DCR.

Im not sure on a small block, but on a big block chevy, for every cc you want to reduce by milling the heads (make the chamber smaller), you have to mill .005/.006 on the average. Check with a machinist, there must be a similar number for small blocks. You have to do some figuring to come to the answers you're looking for. My concern is that you mention a huge cam....Im not sure what you have, but a huge cam will not make a strong engine...just the opposite in fact. There are a lot of parts that go into the combination, and they ALL have to work together. Overcamming an engine is by far the most common mistake made...and you will for sure not be happy with it in the end. It might sound nasty, but will fall on it's face. Big cams need lots of compression (and lots of converter too if it's an automatic) More compression = racing fuel at a certain point. Rumrumm is right, keep the dynamic around 8/1 or so. My static c/r is 10/1, and dynamic is about 8.3....I run iron heads on my BBC with 92 or 93 octane with no problems. But I woundnt want to push it much more. Post all your parts and their specs, and Im sure you will get lots of good info. John