[Guest]

How much difference is there between 3.4 and 3.55 gears open rear end.
I estimate approx. 100 RPM more AT 55 MPH.
But what about off the line, will there be much difference.
I have a 65 mustang, 289, 225HP, c4 with mild shift kit and 2.80 open rear end.
Thanks

 

[camachinist]

If you're changing from the 2.80's, either gear ratio will be a big improvement in off-the-line feel. I ran 3.50's in my street racer back in the 70's and felt it was an ideal compromise between everyday driving and racing (67 with 289/C4)...

Look into a looser converter for the C4 as well...I really liked the performance of the 11" unit I ran....doesn't compare to the 8" units I've run in the race car over the years but is a big improvement over stock.

Assuming a 25" tall tire and no converter slip, your rpm at 55 with the 2.80's would be around 2050rpm; with the 3.55's, it would be 2560rpm or so and, with a 3.40 gear, the rpm would be about 2490rpm.

Hope that helps!