I have a Tremec T 5 behind a 286 inch blown EAB Flatty in my '29 Tudor. The differential is a Winters V8 quick change 4.11. Tires are 30 inch Firestone cheater slicks. I love everything about the combo except for the OD ratio. The .63 5th gear OD falls flat when selected at 60 mph. Living in rural Wisconsin, I don't really do much interstate driving. With the current set-up, cruising under 55 is ok. Tremec doesn't offer a steeper OD that I can find from their literature. Any suggestions ?
I suggest you learn all about the transmissions, and what parts interchange with what. There was a very wide variety of gear ratios offered, but they usually came with different case bolt patterns, input shaft size/spline, shifter location, etc. http://www.britishv8.org/Articles/Borg-Warner-T5-ID-Tags.htm has a few listed with much better overdrive ratios for your application.
The first thing I would do is take advantage of the Q/C and raise the ratio to try and match the O/D RPM and highway speeds you normally like to run. Your blown flathead should be comfortable in the 1500-1800 rpm cruise range, unless the cam is on the "wild" side.
The "World" class T-5 is also available in .83 OD ratio, & is typically available in lower powered (especially foreign customer) vehicles(Isuzu, for example) that didn't have the torque to "pull' a deeper OD ratio.
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