I'm doing a frame up restoration on my 75 F250. Would like to keep the engine original in appearance, but want to modify it somewhat. The engine/truck only has 62,000 miles on it and runs very well. Someone recommended a different cam, a 390 crank, and different pistons. Any comments or suggestions?

Thanks,

Joe

 

Welcome to FTE!

The 360 is considered as a dog, by FE standards, as it was designed to be a low compression truck engine. Even with a bump in the compression ratio and a decent cam, they leave a lot to be desired as they only have a 3.50" stroke.
A very common upgrade, is swapping the crank and rods from a 390 to achieve the longer 3.78" stroke. Since these 2 engines were identical on the outside, the only way to truely identify the difference is by measuring the stroke.
The later engines (76 was the last year for the 360/390) have smog era cams and cam timing. This made them a bit less polluting, but a lot less performing.
A mildly built 390, using a comp ratio in the 9.5-10:1 range, and a cam with around 260-270 degree "advertised" duration, and around .500" total valve lift will result in an engine that makes a lot more power/torque than a stock 360, while netting about the same (or even better) overall MPG. Topping this setup with a decent 4bbl intake (even the factory 4bbl is plenty) and a carb in the 600-650 CFM range and adding decent flowing dual exhaust makes it even better. Headers will also improve things, but if you want to retain the "original" appearance, they aren't really a requirement.

How well does this "package" work? Well, it's quite similar to the 390GT used in the mid 60's, so that tells you what kind of power/torque is available, while still maintaining the stock appearance. It can even be used with an auto trans without any real problems, so long as the cam is spec'd correctly.
The only real giveaway that there *might* be a little extra hidden inside that "stock-looking" engine, is a slightly noticable note in the exhaust at idle...... This can be masked with good mufflers.

 

In swapping the crank and rods will I need to go with different pistons? Also would you go with edelbrock or holley carb?

 

Swapping the crank/rods will most likely require a minor overbore due to the wear in the cyl walls, even if the engine is as low mileage as you say. However, the 360 was built with pistons that match the older 390 specs. The cheapest way to achieve a CR in 9.5-10:1 range with 390 crank/rods, is using stock replacement 360 pistons to match the overbore. (360/390 both use 4.050 standard bore). The thing to look for is ~1.76" compression distance (or pin height as some say) like the older 390's used. Newer (68+ IIRC) truck 390's were fitted with ~1.66 CD pistons, to drop the CR into the upper 7's.
This setup will have the pistons traveling higher and lower in the cyl, so any wear would leave a ridge that the rings would have to go past. Hence, the need for a "cleanup" bore of .020-.030 based on both the actual wear of the cyls and available replacement pistons/rings. .020 and .040 oversize pistons/rings were once more common than they are today.

As for which type of carb, it's more a matter of personal opinion. I prefer the Edelbrock for a street engine, while many others prefer a Holley. The Holley was actually factory available on a 75 F250/350 with a 390, so if you are striving to maintain a totally stock appearance, that would be the way to go. Even the stock 2bbl air cleaner would fit on the Holley, while an Edelbrock *typically* needs a short spacer to fit the stock air cleaner.

Holley carbs have a few drawbacks, in my opinion, for use on a vehicle that will not see regular use. The float bowl gaskets can dry out and leak, as can the accel pump. Edelbrock carbs do not use any gaskets to seal fuel below the top of the float bowl, and the accel pump is completely internal, so niether can cause fuel to leak onto the the engine. They do have one drawback though, more than 5.5-6 PSI fuel pressure can lead to fuel "leaking" past the needle/seat assemblies, so a regulator is often needed on a ford, as the mechanical pumps tend to output 7-8 PSI. Holley carbs can easily cope with this supply pressure, so a fuel pressure regulator is not typically needed.

 

Sounds good, thanks for the information!

 

I'm doing basically the same thing with the same engine.
My '73 started life as a 360, it's now a 390 (395.77 cu. in with a +.030" overbore). It has an Edelbrock 2105 intake, Holley 780 cfm carb, a mild hydaulic Competition Cams cam and kit, with the stock 390 4bbl pistons I'm running about 10.2:1 compression. All this exhausts through stock exhaust manifolds.
All this but the engine, in my opinion, still looks stock.

 

Isnt a 780 cfm carb a little big for a mild build 390?

 

I was thinking the same thing.

 

Yeah, it is, but I got a deal on it I couldn't refuse......FREE!
If I can't fine tune it to my liking, I'll get a 650 and replace it.

 

Free is a hard price to beat. Paid the same for an edelbrock 1405 with less than 50 miles of use, but it came with a complete car bolted to it, and a couple holleys in the seat. The car was packed with lots of parts, the rest had to go in the back of the truck.

That engine looks nice. I also have an edelbrock 2105 that has been painted. I detailed the "Edelbrock" and "Performer 390" like your pic shows. I plan to do the same with the valve covers and the "Power by Ford" stamped in them.
It's little things like this, that can really dress up an otherwise stock-looking engine, and mine just happens to be hiding 390GT internals in a truck block and heads. May not be the most powerful, but certainly better than the stock de-tuned 390 delivered from the factory.

 

Which model Holley carb would be the most "stock" appearing or the best fit for this engine when I finish it?

 

Holley 600-650cfm 4bbl w/ vacuum secondaries and electric choke.

 

Agreed.

 

And the optional ford kickdown linkage, if you have an auto trans.

 

Thanks guys!