help me, miscalculated comp ratio

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Sep 21, 2009 | 01:43 AM

Draken

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help me, miscalculated comp ratio

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?

Sep 21, 2009 | 04:09 PM

beartracks

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From: Albuquerque

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.

Oct 3, 2009 | 11:15 AM

fordeverpower

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From: iowa

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.

Oct 3, 2009 | 07:12 PM

Mustang6147

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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.

Oct 4, 2009 | 12:37 AM

johnboy427

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From: The Vieux Ford, Kansas

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

Oct 4, 2009 | 12:10 PM

doug1222556

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Quote:

Originally Posted by fordeverpower

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.

Oct 16, 2009 | 03:16 AM

Draken

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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