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?

Way above my pay grade but isn't there a grade of methanol above the "regular " stuff that can support more compression? I thought I had read about some NA alcohol engines that were in the 16:1 range but I suspect it would be all about the combination, combustion chamber shape etc.

Kevin

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.

No personal experience but I know some Chebby guys that are serious bracket racers .... 16 to one with alum heads !

They love the combo !

I've heard that 16 to 1 is the best for N/A drag racing also from some reliable sources that drag race on standard production methanol not M1 or M5

Call the fuel company tech line and see what they say. VP racing tech guys are super sharp so if you local track has VP fuel give them a buzz and see what they say.

As much compression as you can make...16 to 1 is by all means not out of line on methanol. I have the understanding more compression = milder camshaft also when dealing with methanol or should I say an easier on parts type of camshaft. I am no rocket scientist but will be shooting for as much compression as I can get into my combo and it is injected alky. But there is alot of people that think over 14 to 1 is a waste...

I was 15.3 with a sb, injected on alky. Ran real good, would run more next time.

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.

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.

I run 12:1 static with a roots at 15 pounds. AF is generally in the high 4's

If you are worried about the increase in c.r., can't you use a thicker head gasket to reduce it some?

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.