Reply With QuoteIt seems to me that 11.8:1 compression is a lot for non-forged pistons and cast iron heads. I would try backing the timing down to 34 degrees total, run the AV gas and watch your plugs.
You may need to switch to open chamber heads.
My .02
i have a jet w/a .030 over 454 w/KB hyperutetic pistons (.133 dome) using fully closed oval port heads, manley severe duty SS valves, tunnel ram w/ 2- 700's (Holley). According to summit this combo makes 11.8:1 +/-. The motor seems to like 38.5 degrees timing w/msd pro billet dist & 6al
i currently run 100% 110 fuel but it cost 3.50 gallon. can i run 110 lo lead av gas (1.80 gal) or mix my current fuel w/ 93 octane pump gas? PLEASE HELP. I have visions of a LARGE fuel bill this year.
It seems to me that 11.8:1 compression is a lot for non-forged pistons and cast iron heads. I would try backing the timing down to 34 degrees total, run the AV gas and watch your plugs.
You may need to switch to open chamber heads.
My .02
Drop a little timing and you can run 92 octane. Everyone freaks out about comp ratios and race fuel. Unecessary. I ran 11.75-1 comp in my truck and it would digest any gas I fed it with no adverse effects. Well, it didn't like to shut off on 87. Run 92 octane and drop your timing to about 33-34 deg total.
i think i might mix avgas and 92 or 93 50/50 and make sure you dont run it lean. also they make copper head gaskets that will give you a few more cc's and run your boat at 150 degrees if possable. also you can run cooler plugs. but the real fix is greater cc for the heads or low comp pistons. .02
I would re-think mixing av and regular gas, while this will work, av and regular gas are of different density causing them to flow different. If you dont get the exact mix every time this will cause you to run to rich or lean depending on the mix. I have run straight av for the last 3 years in my current motor (13-1) and no problems.
Someone on this board mentioned this once... With the all the cost with making HP, the fuel is the cheap part. If you can afford the motor, you can afford the fuel. I run Sunoco 110 in my blower motor and 87 in my ski boat. Both motors are set up to run their specific fuel. My suggestion is to decide if you want lots of HP or detuned for pump gas. I know you can make plenty of power on pump gas and it is available everywhere, just you can make alot more with race fuel. just my .02
mrgoslow i run 11.5:1 on pump gas with no prob(500 ci TALL block) 92 super bitchen sometimes ill throw in av but not that often with arais dome pistons very big polished alum bow-tie heads 2-1050 dominators 750-hp but i would go with unchaineds idea about droping to 34 i run a mag currently and at high timing it had sum kik ass ghosts flying out of the scoop---nasty
Just asking, are you sure about your compression ratio? I'm running a bbc 454 +.060 with .100 dome, .005 deck clearance and 1967 closed chamber heads that CC 108cc. My combination measures out to 9.6 . Runs fine on 92 with no pinging.
thanks for the input. i now see the light. if i want the power suck it up, buy the fuel & give it timing. if not loosen the screws and let it eat. thanks.
wrightnow, no kiddin on the avgas? a guy told me he has run his backup motor (11.5:1 427) on straight av gas for years but numerous other people have told me it was too dry. hell, ever rubbed 110 on your fingers?
wsm9808, there are many different factors to consider. the difference in pistons, the fact not all heads of same cast will still cc the same (machining), compressed gasket thickness. besides id say the compression is there. its runs 10-12 mph (depending on weather) faster than my previous motor.
Are you sure about that compression ratio of 11.8 to 1? Normally, it takes a much larger dome on a piston (like 0.500) to get a C.R. that high. Of course, I'm not familiar with "fully closed" oval port heads, but it seems like there may be a problem with the math here. I believe normal closed chamber heads run about 105 to 110 cc's, and open chambers run about 118 cc's. If your chambers are in the 105 to 110 cc range, It's likely that you are not making 11.8:1 compression with a relatively small dome height. You might not need the fancy gas at all.
SteveM.
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