CWerner

So as I get deeper into my LS 480 hot cam swap, I've decided I should pull the rear diff and get it rebuilt. I now have the choice/decision to change from my 3.08 rear gear to something else.

The car will be a primarily a stop & go, cruiser car. I doubt it will see the 1/4 mile more than 1 time per year, if at all. Here in Houston I get a lot of stop and go freeway time also due to the great traffic we have.

So, what at the suggestions and why? I'm leaning towards a 3.55, but the 3.36 is also a good consideration.

gerry72

You want to shoot for an overall gear reduction of between 9 and 11:1 in First gear. I don't know what the First gear ratio is on the referenced trans, but let's just go with 3.0 for demonstration purposes. If you kept your 3.08 gears, then you'd end up with a 9.24 overall. With the tall Corvette tire, this will work but you are at the very low end. If you went with a 3.36, then your overall is 10.08 -and so on. Below 9 and the car just won't pull easy out of the hole. Above 11 and you run out of gear and, in stop-and-go traffic, it could mean you end up having to pull a shift at those intermediate speeds.

This isn't an absolute for every scenario. For example: If you make a lot of low-rpm torque, then it becomes easier to drive the car at or below the 9. It's just a ballpark range for a street car. Engine parameters, drivetrain, vehicle weight, tire diameter, how the car is used...all and more go into the consideration, but you have an idea of where you need to be.

Garys 68

I'm running a 400hp LS in my 68 with a 3.08 rear, pretty close to yours.
The Richmont 6 speed I have has a 3.28 1st gear, almost the same as your rs500. I would not go with a higher rear unless you have sticky tires and plan on running 1/4 mile lots. That 1st and a 3.08 is a great combo for street driving, and the LS has plenty of torque to break the tires loose.
My OD is 0.76. I went with that because I was concerned with too much gear (ie 0.63) for hills and passing without downshifting. Once again I underestimated the LS torque curve. Your 0.68 OD will be fine with the 3.08.
Keep the 3.08 for a street driven car. Keep in mind gears like 3.55+ were typically used with a 4 speeds 2.6 to 2.2 1st gear.

qwank

3.08 is perfect for the RS500. spend the money elsewhere

gkull

I think about the OD gear ratio. That is why I drove around for 20 years with OD and a 4.11 rear. I even put a 4.10 in my 98 c-5.

It really makes it easy to take off from just and idle. My TKO 600 one time had the shift come apart when I was 20 miles from home and it was stuck in 4th gear and I made it home.

4.11 X OD = effective rear end ratio. The higher rpm your motor is the higher the rear end ratio needed.

I always thought that a 3.90 was about the best. I just had to much money in my Tom's 4.11 to change it out

BB2B

I'm running a TKO 500 (3.27:1 first gear) with a 3:08:1 rear. I installed a high torque comp cam in my 400 cu. in. and can say it is a great combination. Cruising free ways at 1800 rpm in 5th and more than enough gear to get moving.