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View Full Version : New to Forum, 67 GTO 3.73 posi overkill?



67Goat
06-30-2010, 10:04 PM
Hey guys I'm new to the forum!

I'm planning on redoing my rear diff next week and need some advice.

Stats on car:
67 GTO 400cui bore over .30, forged steel pistons, mild cam, headers, street avenger 670 carb, edel performer intake mani, TH 400 trans with 2,400rpm stall and mild shift kit.


So my question is do you think 3.73 gearing is a bit overkill? I try to avoid highway driving as much as possible (rock chips, etc) but I do drive a couple 30-40mile trips to car shows and what not. How bad is 3.73 on the highway compared to say 3.55?

Any advice would be greatly appreciated!
Here's a pic of my car...
https://static1.pt-content.com/images/noimg.gif

big gear head
07-01-2010, 04:03 AM
You will probably not like the 3.73 on the highway. A 3.55 will still gove good performance and be a little better on the highway. Do you have the BOP 8.2 10 bolt? Gears might be a little more expensive for this rear end. Many places sell 8.2 Chevy gears and a adapter for the yoke instead of making gears for the BOP 10 bolt.

Josh69
07-02-2010, 09:31 AM
I have 3.73's in my car with an overdrive. If I stay in 4th (1:1), it's pretty annoying above 50mph. For city it's nice, a 3.55 would be better on the road, but probably hardly noticeable. I would play with some gear calculators and figure out what RPM range driving your car is the most annoying at highway speed, and avoid it. A couple hundred RPM may make all the difference in the world. My car is louder at 2000 than it is at 2200 due to resonance. My OD puts it down around 1800 and it's good. Without OD I'm around 2500 in 4th with a 26" rear tire.