360 or 390 crank?
Cargo Master
Joined: Apr 2004
Posts: 2,574
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From: Golden, CO
For the same cost in machining and balancing you pick up 30 cubes and 1/4" stroke.
You need the short rods to go with the 390 crank. Your 360 has longer, lighter duty rods, not the best way to go.
You need the short rods to go with the 390 crank. Your 360 has longer, lighter duty rods, not the best way to go.
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Freshman User
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I haven't noticed much difference in part interchange they use the same cam and if you put oem 360 pistons in a standard duty 390 it raises the compression ratio? I may be wrong here but if you buy aftermarket pistons or cams don't they fit either engine?
Cargo Master
Joined: Apr 2004
Posts: 2,574
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From: Golden, CO
Bolt on is one thing, how they work together is another.
You are right about the 360 pistons making more compression in a 390. Ford used different piston heights to do the same.
When you start shopping cams, you'll notice manufacturers recomend different compression ratios for the different grinds. You need to think about your intended usage, pick the cam that best suits the usage, and build in the compression that suits the cam.
You are right about the 360 pistons making more compression in a 390. Ford used different piston heights to do the same.
When you start shopping cams, you'll notice manufacturers recomend different compression ratios for the different grinds. You need to think about your intended usage, pick the cam that best suits the usage, and build in the compression that suits the cam.
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To tell ya the truth my '71 F-250 4x4 is going to be my only vehicle I'm building it to handle everyday use including road trips (granted it'll prolly be alone) and some people laugh at that and say "why would you want some old POS without power steering, a/c, power seats, power windows, on star and OBD-17?" Then I try to explain how I feel "At Home in em" but then they just think I really have issues! So that being said I guess I am trying to figure the best way to build a strong and reliable FE and need some good advice cause this is the first one I've been around I always had 351's 400's or 460's. I want to stay fairly stock (enen the old 2v motorcraft and intake) was thinking 9.5:1 or 10:1 pistons a mild cam and sounds like 390 crank and rods now? That's my plan so any other advice about weak points/upgrades for what I'm doin would be greatly appreciated! I have access to alot of old fords via fellow farmers junk piles so parts are definitly available just need to know what to snag!!
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Posting Guru
Joined: Jul 2003
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Using the stock 360 pistons will lower the compression ratio.
Stock 360 rods are longer than stock 390 rods, so the piston pin height on the 360 piston is higher than the 390 piston. So if you put a 390 rod on a 360 piston, the total length will be shorter than a 390 piston on a 390 rod.
Therefore lower compression.
At least that is my best guess, I do not work with 360 or 390 engines.
Stock 360 rods are longer than stock 390 rods, so the piston pin height on the 360 piston is higher than the 390 piston. So if you put a 390 rod on a 360 piston, the total length will be shorter than a 390 piston on a 390 rod.
Therefore lower compression.
At least that is my best guess, I do not work with 360 or 390 engines.
Postmaster
Joined: Aug 2005
Posts: 2,760
Likes: 8
From: Gadsden Purchase
Using the stock 360 pistons will lower the compression ratio.
Stock 360 rods are longer than stock 390 rods, so the piston pin height
on the 360 piston is higher than the 390 piston.
So if you put a 390 rod on a 360 piston, the total length will be shorter
than a 390 piston on a 390 rod. Therefore lower compression.
At least that is my best guess, I do not work with 360 or 390 engines.
Stock 360 rods are longer than stock 390 rods, so the piston pin height
on the 360 piston is higher than the 390 piston.
So if you put a 390 rod on a 360 piston, the total length will be shorter
than a 390 piston on a 390 rod. Therefore lower compression.
At least that is my best guess, I do not work with 360 or 390 engines.
The rod length difference is less than 1/16" (~.050").
Since the stroke difference is ~1/4"...
To get the piston's top up near the top of the 360's cylinder...
The piston's pin would need to be lower on the 360's piston.
Alvin in AZ
Posting Guru
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Something about all that seems backwards to me.
The rod length difference is less than 1/16" (~.050").
Since the stroke difference is ~1/4"...
To get the piston's top up near the top of the 360's cylinder...
The piston's pin would need to be lower on the 360's piston.
Alvin in AZ
The rod length difference is less than 1/16" (~.050").
Since the stroke difference is ~1/4"...
To get the piston's top up near the top of the 360's cylinder...
The piston's pin would need to be lower on the 360's piston.
Alvin in AZ
Postmaster
Joined: Aug 2005
Posts: 2,760
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From: Gadsden Purchase
for a 390 crank and rods anyway?
If a guy was going to go the "new fancy after market" route might as well
get a 410 crank? ;)
Alvin in AZ
Posting Guru
Joined: Jul 2003
Posts: 1,287
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If you are going to buy aftermarket, then I would go with the 4.25 stroke, with a 4.080 bore you get 445 cubes for $1,850.00. Why stop with a 3.98 stroke if the price is close to the same. That price is for the complete balanced kit from Survival Motorsports.
Logistics Pro
Joined: Oct 2005
Posts: 3,785
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From: Mddl A MexCans
The 360 piston pin height is lower (from the top f the piston) by .012" IIRC bought a set to go in my 390 build. This has been discussed so many times hear anyone could find the answer in a jippy. If you look at a a 65' or so 390 4V piston the pin is the same height. The pistons sold with most kits for a 390 now are actually a 410 piston.
I'd just build a solid 390 and be done with it. It'll serve the purpose and for far less $$ than a stroker which wont be of much use as a daily driver IMO.
I'd just build a solid 390 and be done with it. It'll serve the purpose and for far less $$ than a stroker which wont be of much use as a daily driver IMO.
Cargo Master
Joined: Aug 2000
Posts: 2,931
Likes: 12
From: SW Michigan
360 or 390....pistons
Colodado, you'll want the 390 crank and rods. The 360 is good for nothing.....the only good thing about a 360 is how easily it can be turned into a 390. The 360's 3&1/2 inch stroke is not inherently bad, but there just aren't any good piston choices available to get a proper assembled height. The 390, on the other hand, has lots of piston choices. The flattops from a 360 can work very well. But choose your pistons carefully. 999 out of 1000 shops will try to give you 381Ps or 1139s.......which end up giving you about 7.6 to 1 compression. and that just isn't enough. DinosaurFan