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High Octane
11-21-2007 06:36:18
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Re: How to figure compression? in reply to T Puller, 11-14-2007 05:25:19
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Guido, I take the final compression ratio, example, 10.5 to 1. multiply that by 20, equals the approximate cyl pressure for that cyl specs. I figure, the 20, means 20 psi,, which is 1 to 1,, broke down to a simpler form, that "? to 1" has to mean something mathmatically,, so I took known factors from my old engine,, did all the math,, figured it to be 14.7 to 1. When I ran the cyl pressure test at cranking speed,, I got 294-295 psi of cyl pressure at test. I took the cyl pressure divided by compression ratio, and came up with an even 20. So I figure, 20, means 20 psi per point of mechanical compression ratio,, 1 to 1 is 20 psi,, 1.5 to 1 is 30 psi, and so on and so on,,, Automotive engines, naturally aspirated, wont run with that much cyl pressure,, they will ping detonate,, blow up.. The rpms shake the cyl apart,, so they have to decrease cyl pressure to make it run well, on lower octane fuels,, overlap, or lobe separation angle, allows them to do this,,, and still have the high mechanical ratio,,, but a lower actual cyl pressure to fool the engine in thinking it has a lower compression ratio. Nothing I mentioned above, is writtn in stone so far,,, but if you think about it,, a tractor engine,,, is pretty simple,, the cams dont have overlap in stock form,, and when the compression ratio is increased,, as long as the test is done to know where it was to begin with,, the actual cyl pressure for a mechanical ratio can be recorded and a formula to figure that is very possible. Belive it,,,, or not?? LOL.
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