![]() While 9:1 is a safe number, maximizing compression is a great way to increase power. This is in order for the engine to safely work with pump gas, which for much of the country, is limited to 91-octane. 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. The standard recommendation for street engines running on pump gas has always been to shoot for a 9.0:1 to perhaps 9.5:1 compression ratio. 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. Compression Ratio Calculator Extended compression ratio calculator that takes into account factors that are usually missed on other compression calculators. 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. The equations above show the expression for the loss of stroke, l loss, and the effective stroke length, l loss. Enter the measurement designation in either inches, 1, or millimeters, 2. 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. Engine Compression Ratio (CR) Calculator This calculator requires the use of Javascript enabled and capable browsers. For a pump gas street type blown engine I would run 7. Roots blowers cant get away with the compression and boost that a centrifugal superchargers (pro charger, paxton, vortech), and turbos can. 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. with an 8-71 you better have LOW compression and very good bottom end parts. 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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