390 purchase questions

[9299Fords]

I'm looking at picking up a 1972 F250 for a parts donor for my 1950 F2. Beneath it's hood lies a 390. On checking out the spec.s for the different years, the 1972 looks pretty sad at 201 hp and 8.2:1 compression. '68 thru '71 show 255 hp and 8.6:1 CR. I've seen it posted in several places that the '72 FE heads were among the best performers. What did Ford do to drop the CR so low and squash the hp? Dish pistons?

[80broncoman]

The power might also be mcuh closer to same that the numbers show I belive the 71 numbers were gross HP ratings and the 72 were net.
Making a performance engine out of a truck engine is easy. Compression and cam timing were I belive the differences.

[Bear 45/70]

It's true the numbers look low, but the power rating system changed. They no longer rated an engine with no accessories (gross power). After 1972 the engine were rated runing the water pump, alternator, air pumps and in some case the transmission. The real numbers are closer to the post 1972 rating.

[9299Fords]

Thanks for the info. I still wonder what they did to drop the CR from 8.6 to 8.2.

[Hypoid]

A half point? Not sure, but others will know.

One thing Ford did to change CR was change piston pin height: Same block, same head, different piston. Look at the car specs and you find listings for 2V and 4V induction with different CR. If I remember it right, the "4V" 390 piston is the same one found in your garden variety 360. Those bean counters were pretty thrifty, they made it easy to add power with stock parts.

The high performance stuff was different: Bigger valves, different cores to maintain wall thickness, some had different valve spacing. You are talking high $$$ to build with those parts.

[9299Fords]

Originally Posted by Hypoid

A half point? Not sure, but others will know.

One thing Ford did to change CR was change piston pin height: Same block, same head, different piston. Look at the car specs and you find listings for 2V and 4V induction with different CR. If I remember it right, the "4V" 390 piston is the same one found in your garden variety 360. Those bean counters were pretty thrifty, they made it easy to add power with stock parts.

The high performance stuff was different: Bigger valves, different cores to maintain wall thickness, some had different valve spacing. You are talking high $$$ to build with those parts.

I hadn't thought of pin height. I've seen lots of different piston top configurations and thought it might be there.

Doesn't really matter. If I decide to go with the '72 I'll be pulling heads, changing bearings, rings, pistons and throwing a new cam at it.

[Hypoid]

Maybe both! Then you can play with gaskets, and actually the heads have different chamber volumes and runner sizes across groups of years.

I've been thinking about the guy who wants to do a budget 352 build, and how he can bump the CR with stock parts. I just don't have the free time to start running numbers for him.
http://www.ford-trucks.com/forums/73...l-economy.html

There is another forum that has more car related questions, but remains a good source for FE information.
332-428 Ford FE Engine Forum

You can always hit up Barry_R. He was a sponser here, but us poor-folk don't give him enough biz to justify the advertising dollar. He'll gladly answer questions all the same, and he won't sell parts that he wouldn't build with.
Survival FE Engine Kits

HTH, keep us posted.

[80broncoman]

IIRC there are at least three different pistons for 390s
One a flatop with 4 valves eyebrows gave 10.5 to 1 in the older 4bbl motors.
Another flatop with 4 eyebrows AND a small dish gave 9.5 to 1 for 2bbl motors.
Then you had the truck engines which were always in 8s as in 8.6 or 8.2 to 1
I was always under the impression the trucks had a deeper dish piston.
The change in the 71 to 72 years asked about could something as simple as a different thickness head gasket.
On some ford engines in 72 (351W and 429-460) the deck height of the block actully changed by about .022 of a inch.

[390428cjt]

The 390,s had 410 pistons the 360,s were the dished 352 pistons,, there were different type of pistons for the 390 as stated in the earlier post there were chamber volume differences in the heads as well that changes the compression ratings,, milling the heads will change the compression # but anything over 0.30 needs the intake manifold milled as well. The deck height didnt change for the FE motors 10.77 ctr of crank to top of block unless milled by a shop or PO.

[Bear 45/70]

Originally Posted by 390428cjt

The 390,s had 410 pistons the 360,s were the dished 352 pistons,, there were different type of pistons for the 390 as stated in the earlier post there were chamber volume differences in the heads as well that changes the compression ratings,, milling the heads will change the compression # but anything over 0.30 needs the intake manifold milled as well. The deck height didnt change for the FE motors 10.77 ctr of crank to top of block unless milled by a shop or PO.

360s are a 4.05 bore and 352s are 4.00" bore, no interchange there. 410 pistons have the piston pin .010" higher in the piston and can have piston to head clearance problems.

[390428cjt]

The overall length of the piston/rod on a 360 is longer than on a 390...the 360 pistons would stick out of the block if you just swapped in the 390 crankshaft. You can use the 360 pistons OR the 360 rods in a 390, but not both. (That's how 360's were built...using the 390 piston. The compression height of the 390 4V pistons with the long 352 rods and 3.50 stroke crank made 8.2:1, 390's used the 410 4V pistons to bring it down to 8.4:1.) The compression height of the 360 pistons is 1.776", which makes the perfect 390 piston. The 360 long rod is .052" longer than the 390 short rod, which combined with 1.680" compression height 390 truck pistons would also give good compression. However, the 360 rods are somewhat weaker than the 390 rods.

you are correct my bad on the 352 pistons but this is the real skinny on the rest!

[9299Fords]

Thanks for the information guys. It's much appreciated.