Hey y'all..
I'm tearing apart a 360 and a 390 to make one good 390 engine.
I was told the 390 came out of a '67 truck, but when I yanked the pistons they turned out to be 390 4v. (car pistons)
After pulling the 360 pistons I noticed how amazingly similar they looked to the 390 pistons. I heard Ford used 390 pistons in the 360 engine, but these Pistons have 360 cast into them. Well most of them anyways, 3 of them looked like they were replacements. Who only replaces three pistons??

Here's where I'm going with this..the 360 pistons seem to be in slightly better condition than the 390 4v pistons. Could the 360 pistons put me at any disadvantage? (compression height etc) or are the 390 4v pistons with a different number?
Also..I'm using 390 crank and rods, c8ae-h heads decked .006..can anyone guess my CR?

 

I also could not see any difference in rod legnth between 360 and 390 to my naked eye..I know they're different, but I have a slight suspicion that someone may have done this swap on the 360 previously...because the crank looks the same to my eye too! I haven't put a measuring tool on it yet, but I thought it would be noticable to my naked eye. No?

 

Give us some casting numbers off the crank and someone should be able to tell. It should be stamped in one of the weights.

 

I'll have numbers for the crank tomorrow, I left the shop for the night..however what I'm really curious about it piston stuff as it will determine what goes into the engine im building

 

360 piston + 390 crank and rods = 9.8:1 ish compression.

 

Perfect Thanks!
My goal was better than 9.5/1 as thats what my cam wants.
I'm curious what I would need to pop my compression into the 10/1 range..they did it stock in the 60's, what bits do I need?

 

They also had high octane gas with lead in the 60's. 10:1 on pump gas is asking for detonation IMHO

 

I've always run 91 octane no ethanol in the '65..realistically I'm curious what cr I can go before worry about pinging.
I have a feeling its well above 10:1

 

Mine's at 9.2:1 and will ping on regular - not a problem as I now refuse refuse to put the ethanol garbage in anything - unless they ever get enough E85 stations around in which case I may bump my compression up a bit.

I have my timing at twelve degrees too though.

 

You can easily go 13:1. You just need to bump the octane up to 120.


Seriously, though, too many variables to give a hard number. Timing, cam duration, lift and overlap and other variables like the coil and ignition you are using, spark plugs. Even the elevation you drive it at can have an impact on what works best for each individual. An engine is a system that should be designed to work as a unit. Preferably with an eye toward the intended use.


If I say you can go to 10.5:1 without pinging and you build it just like that and it pings...then what? Am I liable?


You might want to work with a machine shop to come up with the engine specs that meets your needs rather than asking an arbitrary question of a bunch of strangers.


Good luck!


.

 

Aluminum heads are said to let one run a littler higher compression. After I built my 416 I got tired of the garbage they sell us labeled as gasoline and now refuse to build anything other than a diesel - although I have been doing a lot of thinking about upping the compression in my 416 and running propane.

 

360/390 were introduced in 1968. 1965/67 F100/350: Only V8 available 352 2V.

360 pistons are not the same as 390.

 

Not all 390 pistons are the same as 360 pistons - but all 360 pistons are the same as higher compression 390 pistons - unless you consider the cast "360" on the inside of the skirt as making them a completely different piston.

 

360 pistons are 360 only, not the same as 390.

Left: 1968/72 / Right: 1973/76

6108 piston:

 

For trucks, yes that is the case.