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Ls hp to compression calculator12/6/2023 039 Fel Pro.this negates quite a bit of the increase you are seeking.you can run a steel shim head gasket.but I do not like to with aluminum heads. There several other things to consider.ġ) The factory built engines with a steel shim. This engine is suppose to come in at 8.5 to 1 but is actually about 7.9 to 1. actual compression as built on an assembly line at a factory.Ī good comparison is the old faithful Targetmaster/Goodwrench V8 that they have been selling for about 30 years. Lars is 100% correct on the advertised vs. Obviously, the ones I have torn down have been torn down due to problems and issues, generally caused by poor workmanship in general, so it's not surprising that these second-rate engine builders have not accurately determined the actual compression ratio. I have torn down and measured quite a few "crate engines" (not GM engines) and I have never found the actual compression ratio to be as advertised. Unless the builder has actually measured all specs and volumes, he is assuming a "blueprint" compression ratio, which in most cases will not be correct. If you're buying an engine from GM, the heads and specs are at the standard factory tolerances, and are not at "minimum allowable chamber volume." Many engine builders (other than GM) will use GM components, including heads, and will advertise compression ratio assuming the "advertised" chamber volume rather than the actual measured volumes. It depends what you mean by "crate engine." Any more, anyone who sells a rebuilt or newly built engine calls it a "crate engine." Some of the engine builders are very meticulous with their specifications, and provide accurate data. Am I understanding that changing the heads will change the compression from 9:1 to 10:1? ![]() If you have actually measured all of your parameters (you have cc'ed your piston volumes, cc'ed your heads, measured your deck height, and you know your actual head gasket crushed thickness), and you have done an accurate calculation based on these actual numbers, and you know for sure that your actual comp ratio is 9:1, a change to the 64 cc heads will raise the comp ratio by roughly a full point. The advertised ratios were based on "minimum allowable cylinder head volume" and the deck height at minimum spec, so there were never any production engines that came out of the factory with the advertised ratio. If you then switch from the 76 cc heads to 64 cc heads, the actual ratio will end up being 9.01:1, which equates to an "advertised" ratio of 10:1. Are you assuming your advertised ratio to be an actual 9:1? Keep in mind that the "advertised" compression ratio is typically a full point higher than the actual compression ratio, so the actual 8.06:1 ratio will be an advertised ratio of 9:1. That assumes that your 76 cc heads are really 76 cc's, which they're probably not - they tend to be a little bigger, so comp ratio is even a little lower than 8.06. 035" and flat top pistons with valve reliefs of 10cc's, the comp ratio with your 76cc heads is 8.06:1. 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.You didn't provide any information to calculate this data, but assuming this is a 350 with 4" bore and a 3.48" stroke, and assuming head gasket thickness of. 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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