Compression Question
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Compression Question
I have, what I thought was a stock rebuilt 69 429 in a 68 F250 4x4. It was rebuilt before I bought the truck, so I just did some small checks. It has DOVE heads and the block checked out. The truck never ran like I thought a 360hp engine should, so we started checking things out. First we thought it has a later 4* retarded timing gear in it. It wasn't, so we checked the cam and it was very small by 69 standards. No lift and very little duration. We then did a compression check and it reads 110 pounds across the board, not a 10.5 CR motor, should have read 180psi if it was.
Does any one have any idea what the compression ratio would be for 110 PSI cylinder pressure or what does a 8.0 or 8.5 429 read. Also any cam suggestions. I am trying to get the engine to perform like I know it wants to.
Thanks,
Does any one have any idea what the compression ratio would be for 110 PSI cylinder pressure or what does a 8.0 or 8.5 429 read. Also any cam suggestions. I am trying to get the engine to perform like I know it wants to.
Thanks,
Last edited by fordtruckn; Aug 4, 2007 at 01:35 PM.
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Joined: Jul 2003
Posts: 2,711
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From: Pittsburgh
110psi is about 8:1 or 8.5:1. With that low of compression you won't be able to run any sort of cam, you're gonna have to keep it real small to not bleed off whatever compression you do have.
(cranking pressure+14.7)/14.7 is your approximate compression.
Justin
(cranking pressure+14.7)/14.7 is your approximate compression.
Justin
