I have a 68 coupe with a 302. Looking to upgrade to a traction loc differential. I am not sure what gear ratio I have, and not sure what would suite the car and my driving needs best.

I have a stock 302 with an 8" rear end. I have installed a line lock as well as I had to get some brake work done when I first got the car. I am wanting to have power at the lower end, but will be doing highway speeds a fair bit as well. What does everyone suggest?

Any suggestions would be appreciated.

Greg West

 

i think i would go with some 355s or 3.73s in the rear

 

nobody makes a 3.73 for a 8" so the next one up is a 3.80, but most people do not like them on the freeway with a c-4.

 

I was considering the 3.25 or the 3.55, but don't know what sort of difference it would make, nor am I sure what I have currently. I am going to have to jack it up and spin the drive shaft to see. I also will have to check what the tire size is as well. It is loud as is, and with a wife and 2 kids who like to go on road trips in the car I don't want to be needing ear plugs on a 2 hour drive. Most driving would be shorter trips though.

 

Go 3.55. Quick enough, but won't be screaming on the e-way

 

You either have a 2.80 or a 3.00. A 3.55 is the best choice.You probably wont notice much of improvement with a 3.25. A 3.80 with a 25" tall tire will be very close to 3,000 rpm at about 70 ish on the highway.

 

What do you want out of the car? Different gears for different applications.

 

I went with 3.44s. On basically stock 302 I did not notice that much difference and was a little dissapointed. Now that I'm running my 347 glad I went with these gears plenty good down low and not screaming on highway. If you plan on staying close to stock I would go with 3.55 - anything taller will be reving high on +60 cruising.

 

What transmission are you running? An automatic will have a little slippage compared to a manual trans and will add a few more rpms to the tach on the highway.Tire size (diameter) will play into it as well. I would try to figure out what is the max rpm you can live with on the hwy and then do the math to figure out what gears will work for you.There are lots of online rpm calculators that can help you with this...The ultimate setup is an overdrive trans that will allow you to run a low rear end ratio for great acceleration and an overdrive gear for low highway rpms..For example my brother changed out his close ratio toploader 4 speed trans and a 3:1 rear end gear for a T-5 and a 4:11 rear gear..The car is much much quicker now yet runs the exact same rpms on the highway.

 

I have a C-4 in my 66 with an 8" and I went with 3:55 and it works out perfect. I don't do a lot of highway driving so if you think you will be I would go with the 3:25.