Ive been doing lots of research on FE motors, specially the 390 as I have one in my new to me 1975 f250. I have a couple books ordered and am waiting on them. I want to use the truck for towing a truck camper and general truck duties, firewood, etc. Trucks has a C6 and 410gears, 2wd. I want to improve the power from stock without spending a bundle. Ive read the exhaust manifolds are restrictive so ill be looking at changing them. Also a Edelbrock performer rpm intake. and finally a cam for low end torque.

With these upgrades, cam, intake, and new headers what hp, torque increases should I see over stock? Ballpark ish? Thanks

 

Have you measured the stroke to know for sure that it has a 390 in it. That truck could have easily come with a 360 and not a 390. You can not look at them and tell any difference. You will have to measure the stroke to know for sure. The PO could have rebuilt the engine to 390 as well.

An FE engine turning 4.11 gears should pull like a locomotive as is. It will likely get 6-8 mpg on the hwy at speed because of the rear ratio.

I have a small 4 barrel and long tube headers on my truck. It has 3.25 rear and pulls hard.

I suggest that you use it for a while before dumping money in it, it might surprise you as is.


John

 

Well anything's possible but im pretty sure its a 390, says so on the valve cover, and this truck is very original. I got it off a widow whose husband (who passed) bought it new. Nothing has been hacked on this truck. For instance it has its original am radio. Split rims with ancient bias ply tires. Very clean and original truck. 132000 miles on it.

Im not saying its lacking power, but why not improve things. a little coin for a little extra power. Just curious what these engines are capable of with a little upgrades and where I would be hp and torque wise? Thanks again.

 

All Jowilker is saying is to verify what you have before spending money. Could take you 15 minutes to verify the stroke. Is that too much work?

 

One of the first places for you to spend a thousand bucks is for wheels and tires. You need some safe & modern tires and finding someone to deal with split rims is darn near impossible. 16.5 & 16s both swap on the 8 lug hubs. Do your research, I believe you will find better pricing on 16in.

The FE engine series are known pullers, couple that with that low ratio rear that you have and that truck will pull your hay wagon, or big camper fine as is.


John

 

Take the time to measure the stroke. If it is a 390 or 360 and it is doing what you need it to do, spend some money on the exhaust to start. Long tube headers (as Jowilker stated) work the best for TQ, with dual 2.5 into a muffler and a single 3 inch tail pipe will make the world of difference. It’s not cheap to do it right, then I believe it is the best bang for the buck to start with.

 

Well its a 390 after all, did the spark plugs (old plugs looked good but were sure seized in there) and measured the stroke, engine matches the vin as well. I still want to do the upgrades.
I got a buddy with spare tires and rims for me so that's taken care of. The exhaust is probably what I'll do next, do bad as its almost new. headers for sure. Which headers would fit in my 250? Also back to the first question, what gains could I expect to see from a rv type cam, headers exhaust and rpm intake?

 

Just what are you wanting out of the old truck? A FE 390 turning that low rear ratio is gonna pull like a train as is, and guzzle gas like crazy at 60 & 70 mph hiway speeds.


John

 

If you had drove the truck for a while as is.......you would notice difference with headers. With intake probably nothing but the look( if it currently has 4v intake and carb) with the cam I doubt you would be able to notice anything going with a rv grind.

 

Kinda in the same boat man. I have a 74 w/ a 390. It came w/ a 2 barrel which I changed to a stock iron 4 barrel (because I already had it) and will soon be changed to a Edelbrock Aluminum. The stock exhaust manifolds need to go too. I put dual exhuast on it and it helped. Its like the engine took a big "SIGH" of relief and now is happy but headers will make it happier.

So I'd say exhaust and intake is the place to start without diggin to deep in the motor.

 

Besides weight, you won't notice any difference between the cast iron 4 barrel intake and the performer. Use your money elsewhere unless you have plenty of it.

 

Good to know! Thank you!

 

I guess since nobody's answered your question, I'll bite. The compression ratio is going to be your limiting factor here, but with a better intake (rpm, not the performer) topped with a 650-750 cfm carb (Holley's list #80783 would be a good 650 cfm choice) and an rv cam you can expect 275-300hp and 425-450 ft lbs of torque.