C4 transmission

A 500 cfm carb might be just a little on a the smaller side for a bored, built up 289 but it would still get the job done. I'm just glad to see you didn't over carburete, which is what most people tend to do. The C4 is a very good transmission and it should be good up to 400 hp...nothing you'd have to worry about.

Thanks for the fast reply. I will keep this in mind. I am looking at around 325 to 350 HP

That would not be a very street friendly 289...

If you want a little pep at stop lights, swap out your rear end for some taller gears and right out of the gate it'll feel like you added 50 hp.

C4 trqansmissions

I want to rebuild the motor along with some pep. What gears would I need to change in the rear end? I will have a friend help who knows how to put a motor together. He will help and teach my grandson. I do not know what to do about heads, cams, pistons, what about getting the motor bored, or anything else. I will rebuild in the summer when my grandson is out of school and I want him to help. I would like to know what I need to buy as I would like to get parts a few at the time. If I am asking something crazy, I do not mind someone telling me. I just need some help.

There are several threads on this forum, some recent, about picking the "right" gears for the rear end. If your friend knows how, you can just buy the gears and let him rebuild it. An easier, but more expensive route is to replace the entire third member. As several have reported on the aforementioned threads, I got one off eBay.

As Lizer indicated, the C4 is a pretty stout transmission and especially if its an earlier 70's C4 which had the larger input shaft. You don't indicate what year the C4 is so we don't know what valve body it might contain.

As for the rear end, Charles is spot on. Size the rear end based upon the driving you will be doing and engine mods. The 325 - 350 range is pushing what you can get out of the 289 without having to really invest in some high end heads and parts for the motor. Building a 289 with 300HP + will require some investment. You need to be more concerned with Torque than HP. A good generalized recommendation for rear end size would be something along the 3.50 range.

If the motor needs rebuilt, then a machine shop should perform the norm which is clean, inspect, bore, and possibly deck the block. Have them peen the original rods and install some good oversize rod bolts. New cam bearings. Have the crank ground accordingly. All this is what I refer to as the "norm" for a basic decent foundation for rebuild. Have your machine shop provide the main and rod bearings based on the ground crank.


A decent set of cast pistons with valve reliefs and a good set of rings with the rods installed is not so expensive.

The money will be in the heads, cam, carb, and intake. If your stock heads are of the small chamber size with no provisions for thermactor humps, a good valve job with some exhaust porting will really pep things up. Some will tell you for just a few dollars more you can go with some aluminum heads so its a tough call. A good hydraulic cam sized based upon the heads, intake and carb is strongly recommended. Don't decide this on your own with out some professional help.

If you really want to make sure you assemble this motor correctly, but the book titled "How to rebuild the Small Block Ford" its very well written with good detail for the novice builder.