This is what we call 'compession ratio' most of the time. this is when surface material is removed to lower the piston to deck clearance, increase compression, and make the quench tighter. When blocks are being machined, some people have them decked. Too low though, & you may be risking contact between the piston and an exhaust valve while the engine is running and the valve is open when the piston is at/near the top of the stroke. Quench is the distance from the top of the piston to the face of the head. 3 increase in compression ratio.Īlso, if the piston is deeper, the quench increases. I posted earlier about changing from a stock gasket to a. 039' compressed thickness x 4.166' or something. changing the compressed thickness of a head gasket, and the actual diameter of the bore area can change your comperssion ratio by a half a point or more. Changing any of these changes the compression ratio. Combustion area is the enclosed space above the piston (if any) in the block, the space inside the bore of the head gasket, and the space of the combustion chamber of the head. Lowers compression ratio by increasing total combustion area volume. They change the measurement.all else 0.020'. The distance from the top of the piston (piston to deck clearance or 'down in the hole'/DITH) to the face of the engine block around the bores is a factor in engine behavior. It is almost THE speed secret.Cd is basically how high into the bore the piston is at the top of the stroke. In fact the relationship of cam timing to compression ratio is the whole ball game when it comes to making cam choice and huge power.

The cam has such an influence on final compression figures. A bracket racing engine that is expected to live a long life will give around 175 to 185, A race engine going for power will have as much as 225 PSI but willr equire race fuel and higher rpm. The 1.31 accounts for the principles of Charles law about heat and pressure and is reasonably acccurate for this type of work.Ī good street engine with a stiff cam wil give about 165 PSI. Divide that figure by 1.31 and you will have the actual compression ratio.

make sure battery is charged, Block throttle open. which is the standard for auto race engine info and planning and design. It is almost THE speed secret.ĭesign and Tuning of Competition Engines by PH Smith. A bracket racing engine that is expected to live a long life will give around 175 to 185, A race engine going for power will have as much as 225 PSI but will require race fuel and higher rpm. Static compression ratio is a bit diffferent as it does not allow for the factor of cam timing and therefore is almost useless other than for reference work.Ī good street engine with a stiff cam wil give about 165 PSI. It is reasonably acccurate for this type of work. The 1.31 accounts for the principles of Charles Law about heat and pressure and the 14.7 is the average air pressure at sea level. Divide that figure by (1.31 X 14.7) and you will have the actual compression ratio.

350 chevy compression ratio calculator