What Trans Do You Have & Why ?

[cycleguy55]

I'm running a Richmond Street 5 Speed behind a 460 CID BBF, Final Drive Ratio (FDR) is 2.75:1.

As you can see by the chart below, the Richmond Street 5 Speed is a close-ratio transmission, with a gear spread of only 3.28:1. There's certainly an argument to be made that I don't need a close-ratio box behind a BBF, but I certainly don't need a lower 1st gear (higher numerically) to launch the car. Similarly, I don't need to drop the highway RPMs much, though a little wouldn't hurt (2328 RPM @ 65 MPH with 275/50R15" tires). Switching to 275/60R15" tires would drop the revs about 200 RPM at 65 MPH, though also making 1st gear slightly taller. Hmmm....

Interestingly, the Street 5 Speed is no longer available, having apparently been replaced by the Super Street 5 Speed. The closest box to what I have would be the 2.89:1 1st gear model - that would require a change of the FDR to 3.50 to maintain roughly the same 5th gear RPMs.

Transmission and FDR selection are about what you have and what you want to accomplish. Pick your transmission (and ratios) based upon your engine (torque and where produced in power band), then pick FDR. If you've got a high-strung small-displacement engine you'll probably be much happier with a different transmission than you'd put behind a mildly tuned big block torque monster. YMMV