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. 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. Since an uncut Mopar small-block cylinder measures 9.600 inches from the crank centerline to the deck, and our up-stroke/rod/piston numbers add up to 9.583, the pistons should be. For a pump gas street type blown engine I would run 7.5:1 to 7.8:1 SCR. Roots blowers can't get away with the compression and boost that a centrifugal superchargers (pro charger, paxton, vortech), and turbos can. 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. with an 8-71 you better have LOW compression and very good bottom end parts. 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. This compression ratio calculator can be used to work out the compression ratio of your engine. 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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