The 390 has a bore of 4.05 standard
The 427 has a bore of 4.23 standard
The cranks have the same stroke, although some 427 cranks were steel. Some 390's (FT's found in trucks) have steel cranks, but the snout must be turned down to use passanger car timing chains/covers
Boring the 390 beyond 0.030 over should be done with care, and is generally not a good idea.
The easy way to get extra cubes in a 390 is to run a 428 crank, but make sure you get the proper flywheel and harmonic balanceer as those are detroit balanced, rather than neutral balanced. This gives you a 410 which is a combo sold by Mercury around'66, '67.
The Oiling system on the 390 is the same as on a center oiler 427 (basically). The hydrolic lifter blocks and solid lifter blocks have slightly different oliing too, but you can convert hydrolic blocks to solid lifter.
Some 427's come as side oilers, where the
oil goes directly from the
oil pump to each main bearing, rather than the front bearing then across to the cam bearings and down to the mains.
Personally, I like the 390. Parts are a LOT cheaper than the 427/428, and externally it looks just like a 428. An extra 38 cubes is less than 10% different, and unless you are drag racing, I doubt that you can get the extra power to the ground. Of course, I say this but I have a 428, so maybe I am full of it, although the sticker on my air cleaner says "High Performance 289" LOL
I am no expert, but I think I am mostly correct on this.
Tom Johnson
What's the difference between a 390 and a 427?
Linear Mode
