Good advice, Tech.

Likewise, I have seen folks run OD with as low as 2.75 gears. That puts final drive ratios lower than 2 to 1. That ain't gonna work either, even with a stock cam. My current project car came with a T5 OD and 3.00 gears. Even with a stock cam, it was a dog in OD. Felt pretty good in 4th, though. Even with stock cams, most factory cars are running at least 3.42's.

Some OD transmissions, like the 700R4 have a low 1st gear and can efficiently get away with 3.25's or so, depending on tire size. I've seen factory setups in that range.

Back in the "old days" when OD's were electric shifted add-ons to a 3 speed manual, nearly every factory setup came with 4.11 gears. This gets you about a 2.85 to 1 ratio with typical 30% OD.

I ran a test with my car (the one with the T5 and 3.00's) once when I didn't have anything else to do. I ran a 75 mile loop twice on the same day. Once using 5th gear and once keeping it in 4th. Filled up at the same station, same gas pump. I picked up maybe 1 mile per gallon in 5th, but it's hard to say for sure. I put the fact that it ran OK in 5th down to a well tuned Q-jet (yes those do exist) with it's very efficient boosters that still meter well at fairly low air speed. For no more than I gained (if I actually gained anything), I would have been just as well off with a 4 speed.

My Healey project has a close ratio T56. It has a 2.97 first gear and a .64 6th. My cam will have an advertised operating range of 1200-6000 rpm. Based on that, I could go as low as 3.27 in the rear (which would be about 450 rpms above minimum at 60), but will most likely start out with 3.55's (about 580 above minimum at 60), since I already have a set.

Hope you don't consider this a hijack.