Don't forget you have a longer stroke on the 390 crank using up more of the space up top... The 390 rods are also shorter than the 360's to compensate for the stroke.

--Mike

 

I wish I had listened on the first post. 360 pistons are flattop with only the cutout for the valves. 390 has more relief to lower the compression ratio. I'm still confused as to why the 360 goes higher in the cylinder as the drawings show the pin to top dimension as the same. I ordered a set of 360 pistons .030 over. If there is a deck clearance issue I'll deal with it when I assemble.

 

I've been trying to post my cam specifications but everytime I try it says that I have a website link in the post...why would that be???

 

See if this helps:
Stroke 360 = 3.50
Stroke 390 = 3.784
390 is +.284

Rods 360 = 6.54
Rods 390 = 6.488
390 is -.052

Compression height 360 = 1.776 (center of wrist pin to top of piston)
Compression height 390 = 1.680
390 is -.096

Overall difference 390 is +.136 further up in the hole to the top of the piston over a 360.

--Mike

 

Yes, that's exactly what I'm saying. Unless my book is completely wrong AND the pistons were wrong that I pulled out of my old 360.

Mike, you're sure you didn't use long rods in that 390? That's about the only way I can figure the piston would be above the deck with 360 pistons. Or maybe someone offset ground the crank at some point, knowingly or otherwise?

Falcon, for the cam just tell us what the manufacturer and the part numbers are. We can figure out the rest.

Going by Mike's numbers:
10.17-1.892-6.488-1.776=.014" deck clearance. The 1.892 is half of 3.784.

 

So Rusty would the 360 pistons in a 390 give more stump pulling torque along with a lumpier cam or would the horsepower be higher at higher revs? I have a hard time understanding how you guys differenciate between torque and horsepower. I ask for a 4x4 not a racing truck. ie= mud bogging, hauling, off roading, lugging up hills

 

You guys are full of information! Many Thanks for all the responses! I'm finally starting to get it...it takes time to get through my hard head...LOL. The cam is a compcam 22-238-4.

 

oops...mistype...it's a compcam 33-238-4

 

Increased compression adds efficiency to an engine. This will improve torque at all rpm's. So you will get increased torque and horsepower. In fact, when I increase compression in a Desktop Dyno simulation and change nothing else, the horsepower and torque curves both go up, and their shape remains absolutely unchanged.

Now if you add a bigger cam to go with the higher compression, then THAT will do a lot more for high rpm power. Typically you want to match the cam you use to the compression ratio. Go to cranecams.com. You'll notice that all of their cams list a recommended compression ratio. This is because of dynamic compression, which is figured from when the intake valve closes. Close the intake valve later, and you build less compression at lower rpms. This lets you get away with high compression ratios with pump gas.

So to build a torque engine like you want to, you'll pick a cam with the characteristics you want, and get the compression to the top of the range for that cam. An example would be a Crane 343901 cam, and 9.5:1 compression.

Sorry for the book.

 

Falcon:
That is a 262/270 degree dual pattern cam, with .513"/.519" lift. It should work well for a low rpm torque engine.

 

Hey Rusty books can be awesome (if it is interesting) and yours made sense. What do you think 360 pistons would bring compression up to with no other changes to engine internally?

 

Well...

 

Thanks....Blonde moment. I read that earlier too.

 

okay guys i am gonna but into this thread a little. The truck that i just bought being a 74 f250 supercab has a 390 engine in it. i was told that the engine has a blown cylindar not for sure what that means but never the less would the engine be able to be rebuilt if this is true or would there be a problem with rebuilding it. also i am not very familar with a 390 i know alot about the 351m and the 351c also the 460 but as far as the 390 goes i am in the dark could someone fill me in as far as how buildable is this engine and will it be able to make the truck shoot down the road at any given time with a decent rebuild.Also i am used to the terms of small block and big block what is the 390 is it a big block or a small block? and if those terms are only used on chebbie engines then why in the summit book does it have the 351c listed as a small block ford engine? thanks in advance for the help.

 

Ford likes their medium blocks. They've proven to be juuuuuuust right, between small and big . I would call a 390 a big block.

FE motors are very buildable as described a little in this thread. Theres guys in here that have hella stroked FE's that are really fast! I would go with an FE before I went with any 351 or 460, IMO.