Dynamic Compression Ratio

[bobscuda67]

:scratch: I'm putting together my 340\373 engine and I'm at the point of buying a cam. I measured all the volumes and the static ratio is 8.74 to 1. When I add the rod and cam closing point I get the dynamic ratio at 8.14 to 1. Is the dynamic close to what it should be for a street car? I looked online and everything I read says you don't go over 8.2 to 1 on the dynamic for a street driven car. Why does Keith Blacks compression calculator tell you to add 15 degrees to your intake closing point and others online don't? Makes a big differance in yor dynamic ratio. Can someone enlighten me. Thanks, Bob

 

[lenweiler]

Save yourself some hassle, and possible screwups and have someone spec out a cam for you. Your static compression sounds a bit low anyway. My last 340 had a comp. of 9.5 and easily could have handled another full point without detonation or "rattle''. My stroker is 11.5 and with an open chamber head, I'm still only using 1 gal. of 114 race fuel per tank. Closed chamber heads typically allow more comp. than open, also. Smaller dia. pistons like your 340/373 also allow for higher comp. simply because of better flame propagation, especially with flat top pistons