pistons for 390

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Oct 13, 2004 | 05:39 PM

tastyklair

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From: Eastern Pa

pistons for 390

My son has decided to get married so the nice rebuild is out the window. Now we have to tone it down a bit for expense sake. The 390 has been rebuilt by someone in the past cause it has non matching parts and a 2u crank. I want to get to 9.5:1cr or more importantly I want the dynamic compression to be just about as far as it can be with pump gas. I think that is around 8:1? According to Steve Christs book my pistons which have the dish with the double eyebrows in them, are 9.5:1. Does this seem right? What should I look to get in new pistons and a cam to make this happen. I will be using stock heads with some porting and polishing done, headers, Performer intake and 650 Holley. Someone on this forum is running a setup much like this with a 941 Crane but I can't remember who. Any help appreciated.

Oct 13, 2004 | 05:43 PM

FFR428

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From: CT

What year 390 and heads? The cc's of the heads will help determine the best suited comp ratio for your build. G.

Oct 13, 2004 | 07:00 PM

baddad457

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From: south louisiana

I'm running a 390 with a 10.25 to 1 comp ratio on 89 octane gas, I don't see why you would be concerned about 9.5 to 1.

Oct 13, 2004 | 07:17 PM

FFR428

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FWIW I run 11.1 in my 406 with 92 pump gas. G.

Oct 13, 2004 | 08:54 PM

tastyklair

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From: Eastern Pa

The block is from 65, heads are the C8AE-H which I guess are 68 and later. I have not cc'd them yet but they are supposed to be 68- 72cc according to the books. I would go higher in cr as long as I can make it work with the gas. I guess I should add that I'm running 4:10 gears and a manual transmission.

Last edited by tastyklair; Oct 13, 2004 at 09:05 PM.

Oct 14, 2004 | 02:59 AM

baddad457

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From: south louisiana

My 68 Merc's 390 also has C8AE-H heads with as I said before a 10.25 to 1 comp ratio. Cam is a Crane 272 degree Energizer, pistons are the stock cast flattops. Ignition is the stock points dist fitted with a Pertronix I unit, riming is set at 12 degrees initial. Runs fine on 87 -89 octane gas, only a hint of ping with 87, none with 89.