360 to 390

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Sep 16, 2004 | 03:44 PM

SuperFord

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360 to 390

I have read the FAQ and it left me with one question. If you want to make a 390 out of a 360, it said you need to swap crank, rods, and pistons. The chart shows the 360 and 390 to have the same bore so why couldn't you just swap in a 390 crank. Also would a 390 rebuild master kit work for a 360, or how about a 390 gt 4bbl intake?

Sep 16, 2004 | 03:48 PM

ford390gashog

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From: Brentwood,CA

you need a 390 crank and rods you can't use a 390 crank and 360 rods

Sep 16, 2004 | 04:41 PM

Mike G

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From: Littleton, CO

360 rods can be used, however, they are not as strong (just compare them) and they are a little on the longer side. This causes them to raise the compression to a point that may be too much for pump gas (if you really care about that) for daily driving. The 360 pistons also have a taller compression height, so you really start getting it to the top of the cylinder deck. Now for rediculous HP and compression ratios, this would be no big deal, but for daily driving or reliability, it's a liitle extreme. You also need to keep in mind that your deck may or might have to be shaved for trueness, cutting into the amount of stoke you can play with. The 360/390 share the same block and bolt-ons. Bottom line, use the 390 rods and pistons too for the easiest route (I think that is where you were heading with the 390 Master)....

--Mike

Last edited by Mike G; Sep 16, 2004 at 04:43 PM.

Sep 16, 2004 | 04:57 PM

rusty70f100

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From: Iowa

As was said, 360 rods can be used with a 390 crank. However, you cannot use 360 pistons with that combination. This would be advantageous if you wanted to use the readily avalable 1.66" compression height 390 truck pistons, as it would up the compression ratio to a usable range. If you use the 1.66" compression height pistons with 390 rods and crank you'll end up with something like 8.1 : 1 compression. With the 360 rods it's still going to be low, but it'll be better anyway.

As was noted, the 360 rods are somewhat weaker than the 390 rods. In a normal daily driver this shouldn't be a problem, but dont plan on revs above 6000rpm or any nitrous or forced induction. That results in extra block and oil pan ventilation holes.

Sep 17, 2004 | 09:34 AM

lee

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From: Lacey, WA

Hi,

Not trying to steal this thread but I have a question.

I did this 360 to 390 rebuild last year in my 70 F250 4x4. Used a 2U crank, C7AE B rods, and Silv-O-lite 1139 pistons. Had the short block built up by a local shop. I also have an Edle RPM intake, headers and a 390 GT profile cam.

After I got the truck running I started some research on this combination and found out that the 1139 pistons are for a low compresson (8.2:1) truck application.

Now for my 2 questions.
1. How much of a performance gain would I see if I swapped out these low CR pistons to something in the 9.5:1 range? In other words would it be worth it? Bear in mind that I pull a 4k pound travel trailer sometimes.

2. This engine currently has only 5,000 miles on it. Could I just replace the pistons and rings?

Thanks,
Lee