Compression Ratio Blues

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May 19, 2016 | 08:41 PM

Resto

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Mountain Pass

Joined: Feb 2016

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Compression Ratio Blues

Will my '83 4x4 C6 auto truck perform well with its 302 creating 7.9:1 CR? The 302 is bored .040 over with...72cc combustion chambers (ported and polished - Except intake runners. Stock cast headers and manifold with a Motorcraft 2150. Truck will mainly see mild street, moderate towing and occasional moderate trail use.

I'm considering domed top pistons to boost the CR. The stock combustion chambers averaged 68cc before the P&P.

Some good advise would be appreciated.

May 19, 2016 | 08:51 PM

Conanski

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Joined: Jun 2006

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From: Ottawa, Ontario

It'll run but more compression would be better, consider chalking this up as a learning experience and go find a set of E7, F1, F3 heads to bolt on. All of these would boost static CR at least a full point from what you have now an the F1 and F3 heads could out perform your port job without being touched.

May 20, 2016 | 10:18 PM

Resto

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Mountain Pass

Joined: Feb 2016

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Man the F1 or F3 sound good. Will they match up with my stock intake mani exhaust track for emissions (heat under the carb mount) and will stock headers not be a problem?

Do you happen to know the combustion camber cc?

Thanks again

May 24, 2016 | 04:15 PM

Conanski

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Joined: Jun 2006

Posts: 31,930

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From: Ottawa, Ontario

Yes port locations are all the same so it's a direct bolt on in that regard, chamber sizes is 60-64cc depending upon what motor they were going on.

May 24, 2016 | 09:02 PM

baddad457

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Joined: May 2003

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From: south louisiana

You can always mill the GT40's for more compression, but before doing so, cc them first. The Mustang 5.0 GT40's were milled a second pass to get their chambers to 60ccs at the factory. If they check out at 64 cc's, then you can mill them .040 without running into intake fitment issues. What cam are you running ?