The Stovebolt Site Forums The Shop Area Engine Shop Rear End Ratios

Looking for some suggestions on a good rear end ratio. My Dad set up the truck to pull (which it did like crazy) but I need to change the rear end to something a little more street worthy. I have a 396 under the hood but I am not looking for a 200 mph street rod either. Some fuel economy or at least as much as a 396 and my lead foot can get would be nice as well. Suggestions or experiences with different ratios?

Thanks!

What transmission do you have and how tall are the rear tires?

How modified if any is the engine, cam, carb, headers?

Whats your driving style, easy, quick, fast, old man?

Joe

Good questions....and the answer is I don't know. When Dad did his modifications for farm work I don't know exactly what changes he made but I do know it is not anywhere near the original transmission.

What I do know is that I am putting a different transmission in it because he did tell me the one it is shot. I am at the moment undecided as to the tires I am putting on it. I am probably putting the cart before the horse worrying about the rear end.

Automatic or manual? What size truck? How fast do you need to cruise? What kind of loads will you carry? What are the brakes?

Wow lots of things I have not thought about yet. I am so a novice to all of this.

Brakes...don't know yet. Truck is a C20 and as far as speed like I said it does not need to be a drag truck but I have a 396 so I expect some performance. As far as load carrying. Really none at all. Maybe the occasional sack of grass seed or grocery bags. That is about it.

Find someone who can work out final ratios after you make some decision on tires I am running a muncie 4 speed with about a 3.55 gear. when I had the 245/55/16 tires my speedo was about 10mph too fast. I went to 245/40/20 and the speedo is right but I sure lost a lot of punch.

What year C20? Depending on the year your ratio choices may be very limited unless you swap the entire rear axle.

There are a number of versions of the 396, starting at 325 horse up to 375 and more. If you have the milder motor its a strong motor but nothing scary.

I have a newer big block pickup and sure love that pulling power!

It is a 67. I know the 396 I have is not the high end one but I also don't what the horses are for sure. I will be checking into that soon.

The most likely rear gears in a '67 C20 are 4.57. Those are pretty deep and with a 396 I'd expect it to pull pretty hard.

Your challenge is that there are only three gear sets available for that rear, 5.14, 4.57 and 4.11. The 4.11 would be the most highway friendly but they are very hard to find.

Your best bet might be to look for a Dana or GM 14-bolt with a gear ratio you like better.

Thanks for the info OldSub. I think I might lean towards your Dana or GM suggestion.

If you can find a Dana Type 60 rear axle from a GMC it will be almost a bolt-in swap. Those axles have several good ratios available, 3.73, 3.55, and I believe there's a 3.36 available from Ford 3/4 ton automatic transmission models. Ford, GMC, Dodge, and International all ran the Dana 60 at one time or another. I've got one under a 59 Burb with Ford gears, a GMC housing, and a Dodge pinion flange! It's a 3.73 ratio.
Jerry

It all depends on what you are looking for.In my 55 2nd I have a built 350 engine going into a 700R4 trans,and stock 3:90 rear gears.The 700R4 is an overdrive tranny which works out very good.It also gets 20 MPG all day long.If I was runninmg a turbo 350 or 400 I would want to have about a 3:08 rearend for cruising,and good mileage.The plus with my setup is that the 700R4 has a wicked low gear and it performs nicely,from a dead stop.