![]() 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. pressure as measured off a compression tester guage. As already stated, its impossible to calculate CR with the engine assembled, or by using cyl. Drag Racing Calculators,Calculators to find 1/4 mile ET and MPH, CID,Piston Speed,gear ratio,carburetor size,margin of victory,Engine calculator, Calculates relative horsepower, air density, density altitude, virtual temperature, actual air pressure, vapor pressure and dyno correction factor and more. Any help appreciated thanks tgabbe1934, May 6, 2010. 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. I got a 350 chevy, not sure of the compression ratio, was trying to figure out approximately what it is without tearing down. 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. General rule of thumb for acceptable dynamic compression ratio to run safely on pump gas is 8:1 maximum for engines with cast iron cylinder heads and 8.5:1 with aluminum cylinder heads.Warm engine. However, that same 11:1 static compression ratio engine with the radical 259/269 duration camshaft would have a dynamic compression ratio in the neighborhood of 7.5:1, totally acceptable to run on pump gas. Therefore with the mild cam it will have a high dynamic compression ratio, probably 9.5:1+ which would be way too high to run safely on 91 octane gas. If you put a very mild camshaft (194/204 duration this cam will have an "early" IVC (intake valve closing point), and will "bleed off" less compression than a radical camshaft with 259/269 duration and a considerably "later" IVC. To give an example, lets say you're considering only pump gas for your engine, and it has a static compression ratio of 11:1. Unlike Static Compression Ratio, Dynamic Compression Ratio takes into account camshaft timing by considering the intake valve closing point in relation to the piston position. Static Compression Ratio numbers are the ones you hear thrown around the most ("10:1 compression"), and it takes into consideration the full sweep volume of the cylinder in regard to its range of crankshaft stroke. This calculator will calculate both Static and Dynamic compression ratioĬompression Ratio is the ratio of an engine's cylinder volume vs.
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