Hello Everyone,

I'm thinking of getting a '79 F-150 or 250 4x4 and would prefer a manual transmission.

Are there any aftermarket manual transmissions available for that combination?

What manual transmissions were offered that year?

I'm looking for good highway mileage

Thanks,
Barney

 

Well first you are going to need to know what bellhousing you have. 400, 351m, and 460's have big block bell housings. 302 and 300 have small block bell housings. The manual transmissions offered for those trucks would beNew Process np435's and Tremec t-18 4 speeds. These transmissions have a "granny low" first gear and are direct drive in fourth. If you are looking for highway mileage you're going to want a od transmission, obviously. For a 4x4 truck you are also going to want to keep the low first gear, so you are looking for a granny/od 5 speed. Popular options include Fords zf5 and Chevy/dodge's nv4500. These are popular transmissions that can be found under many trucks in lots of junkyards.

Another way to get low rpms on the highway would be to use a high geared differential. A 3.54 gear would be about as high as you want in a truck, but still let you turn relatively low rpms at 65-75. The cost of gas saved with a overdrive transmission vs the cost of a transmission swap is going to be the deciding factor. Sometimes in town mileage can increase by gearing the differentials lower, making it easier for the vehicle to accelerate from stops.

The np435 and t-18 are very reliable and proven. I have a nv4500 in my 79 f250 and I love it. I also have 3.54 gears so at 65-75 I'm turning very low rpms. I still only get 10-11 mpg if I'm lucky.

If you google gear ratio/ rpm calculators you can enter you tire diameter, differential gear, transmission gear and your speed to be able to tell what rpm you will be at in a given gear at a given speed. With 32" tires, 3.54 gearing, and a direct transmission you're going to be at 2400 rpms at 65. A .71 overdrive will drop you down to 1700 rpm. Regearing to 4.1 differentials would raise it back up to 2000 rpm. So with a od trans and 4.1 you'd have good pulling power and the ability to turn low rpms at high speeds. But you have to decided if spending the money for that is worth it.

 

Wow! Lots of great information there.

Eventually I'd like to build up a 302 for the same goal (mileage), so I guess I'll need the small block bell housing.

I've had that motor in a '69 Mustang and '67 Bronco. Loved it. Decent mileage and all the power I needed.

About the mileage calculator, I read somewhere that you need to look at your cam choice in determining your ideal RPM. Any thoughts on that?

Thanks for your detailed reply.

Barney

 

A 302 in a 4WD F150/250? Not a good combination in my opinion. It'll be powering a >4500 lb. truck... That's about 1000 lbs or more over a 69 Mustang... An early Bronco is relatively lightweight too.

Regardless, build whatever engine you choose for torque at lower RPM rather than horsepower.

 

I agree with HIO in the 302 argument. A 300 will make very close to the same power but do it at much lower rpm. Both are very light engines and will get pretty good mileage considering what they are.

As far as the cam idle goes, generally a more street/ low rpm power band oriented cam will idle smoother, quieter, and at a lower rpm than a more race/ high power band oriented cam. If you buy a off the shelf cam it should have a recommended idle speed listed on the website.

I'm actually suprised you could understand my first post, I just reread it and apparently I shouldn't think to hard early on Saturday mornings.

Definitely make a thread regarding whatever you decide to do. If it could help one person make a good decision it'll be worth it, and we all like pictures.

 

DirtyLarry,

Don't be hard on yourself. Your post was extremely clear and I got so much out of it.

I'm pretty pleased with the warm reception I've received to my maiden post here.

Thanks again

 

HIO,

Thanks for the advice. I didn't think that a F-150 would weight so much more (empty).

Seeing as how the 300/6cyl was put in some trucks I figured I'd be ok with a 302 with all the modern advances built in. I saw some crate 302's at Summit putting out 390hp. Torque wasn't shown :-(

I don't know what '79 302's (or 300's for that matter) were putting out, but I didn't think it was anywhere near that.

I realize it's a 4x4 and not a hot rod so torque is more important than HP, but couldn't some changes be made to focus more on that aspect (torque) to accomplish that in a smaller (hopefully more fuel efficient) package?