351w head size

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Oct 28, 2006 | 09:20 PM

onefiftynut90

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Joined: Sep 2004

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351w head size

I have a stock 1986 f250 351w (and correct me if i am wrong) but I believe the stock heads are about 63cc chamber, with about a 9.1 --> 9.2:1 ratio.
My question is if i get a set of heads with a 60cc or 61cc chamber my compresion ratio will increase.
Will I need to run premium gas?
what kind of ratio am i looking at?

Oct 29, 2006 | 11:27 AM

baddad457

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Joined: May 2003

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From: south louisiana

Reducing the chamber size 2 or 3 cc's will do nothing. To need to run Premium, you'd need to go up in the ratio about a full point and bump the ignition advance.

Oct 29, 2006 | 12:06 PM

Conanski

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Joined: Jun 2006

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From: Ottawa, Ontario

Depends upon the heads on your truck.. but stock should be 64-69cc producing about 8.5:1 ratio.. stock pistons are dished BTW. Dropping to a 60cc chamber will get you up into the 9:1 territory, but regular fuel should still be fine. My motor runs about 9:1 and has no problems with 87 octane.