What's the difference between a 390 and a 427?
 

Is it the bore or the stroke? If it's both, can you make up the difference by stroking a 390?

It is the bore and oiling
 

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

427.......

forged pistons

crossbolted mains

lemans rods

high nickel block ,stress relieved

forged crank

large valves

machined combustion chambers

screw in core plugs

solid lifters


390...........

not

390 is OK if you don't abuse it. There not the best motors out there to start as a core block.

- Bill -

Thanks for the input guys...

Dont feel bad Blykins,,Most folks think a 427 is a bore 390,427 is the only true racing engine ever to come out of detroit,and really has a class by inself,thats my opnion,,I hope not to start another 427 vs whatever thread,,lol,,if your not all out racing an hot 390 or 428 will give you great performance and service,it's just that a max built other fe will maybe get you close to the hp of an out of the box stock 427.I love the idea of your 289 hi po emblems,if I had a small block car,it would for sure say that instead of 427,I have a pic of some way cool 289 valve covers on a real 289 taken in nashville if you would like to see them,I plan to use them if I ever have a small block car,,Tk