uhh, i am in the process of finnishing my 302 build, i have a stock 68 fairlane 302 with comp 268h cam, holley intake and alot of other goodies....here is where i messed up, i bought a set of heads that i thought where standard c8oe 63 cc heads which would put me at 10.8:1 comp, but i found out i actually bought a set of c8oe-f j code shelby heads with 53.5 cc chambers....you can see where this is going, its sitting at 12.5:1 comp......not that im complaining but im sure pump gas is outta the question....octane boost? mix pump with 110 race gas? or propane is my thoughts, any ideas?

 

Snow Performance water and methonal injection! Works excellent but............ You have a ton of compression, more than the cam is designed for. You'll still need some high octane, how much I don't know.

 

what pistons are you running, domes? what cc, and has the block been decked. I really don't think your compression is any where near that. Its hard to build compression in a 302 without domes and small chambers.

 

Your really not running to high of comp, My thought is, use high octane fuel. Set the timeing where it should be, then put the engine under a load. If it detonates, then try octane booster. Your gonna be close with Sunoco 94 though. You will notice HP gains with 110 though.

My Mustang is 15:1. I rather run high comopresion, as apposed to a $5000 power adder. Some big thing hangin off your engine, is not for me. I have run 110 in it with no detonation.

With that cam, I might recomend you try a compression check in a couple cylinders, to see just how high it is. My K code 289 was up at 210 psi per cylinder. It ran fine on pump gas.

Keep in mind for higher compression to be a benefit, you must turn it faster. Instead of a blower, or turbo pushing air into the cylinder, the cylinder must suck it. My bet is, 94 octane will be close.

 

If you have E85 in your area you could switch to that it is over 100 octane.
-Johnboy

 

Really. I'm curious as well. The title may be appropriate here. The change in compression in the cc's doesn't add up for a 302. That amount of cc difference should only raise the comp about a point.

 

i recalculated the compression based on piston deck height, piston cc, gasket thickness, ci of the cyl, and cc of head and came out with 11.3:1 so no worries, i guess i jumped the gun a bit heh

 

Ya know, here's a thoght...
1. thicker head gaskets
2. Water injection
3. Regrind the cam to reduce cylinder pressure.