Max compression on methanol?
#2713527
11/06/19 09:42 PM
11/06/19 09:42 PM
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gregsdart
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For a long time i believed the max compression for a normally s Aspirated motor should be 15 to 15.5 to1. BUT, it was pointed out to me that head limited motors can get away with a bit more because they can't fill the cylinders to the same high percent as a motor with excelent heads. My situation is i am increasing displacement from 528 to 560 cube, and if i don,t cut the domes some the compression will jump from 15.1 to about 16 to 1. 440-1 fully ported alky megablock. .870 gross lift cam, 3x intake and alky injection. Best 8.77 at 3055 weight. Thoughts?
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Max compression on methanol?
[Re: Twostick]
#2713543
11/06/19 10:42 PM
11/06/19 10:42 PM
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gregsdart
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Maybe on the better methanol although i don't know how they would do it. From what i know of methanol, above a certain cylinder pressure before ignition the mixture has to be richened to increase detonation resistance. The power loss of the very fat mixture is offset by higher boost.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Max compression on methanol?
[Re: greendart408]
#2713778
11/07/19 05:36 PM
11/07/19 05:36 PM
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rickseeman
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I'm sure Top Alcohol cars are over 50 lbs of boost. I don't know how to calculate that to compression ratio but I'm guessing it's way over 25:1.
2011 Drag Pak Challenger
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Re: Max compression on methanol?
[Re: rickseeman]
#2713808
11/07/19 07:20 PM
11/07/19 07:20 PM
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gregsdart
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Rick the tuning book i have says blown cars need a mixture of 3.7 to 4 or so to work with those extreme pressures. Normally aspirated equals 5.2 to 5.5. So i am thinking that at some po i n t in raising compression the overly rich mixture needed will cancel any power gains.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Max compression on methanol?
[Re: roadrunninMark]
#2715557
11/13/19 10:12 PM
11/13/19 10:12 PM
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gregsdart
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I could but i don't know what increasing quench distance will do. Plus the goal is to run as much compression as i can without shortening the life of the motor. Thicker gaskets also increase crevis volume which hurts performance from what i have read. The gaskets are 4.6 bore. So the plan is to run a .027 or .036 cometic and cut the dome which is .115 high and should give me enough to work with to bring it down to low 15 range. As is i suspect it will be about 16 to 1. I haven't had a chance to measure everything yet.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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