I have 3.73 gears in my '47' Canopy. I'm running a 46rh behind a 340 and I cruise at 60 mph all day and the RPM is 2000. My tire diameter is 27". The only problem I see is very little torque at that rpm so it takes a little more throttle when going uphill. The gas mileage isn't that great. I thought it would improve when I replaced the 727, but it actually went down. If I was you, I would jump to 3.92's, but do the calculations using your tire diameter to see what your RPM's will be. Use the calculator given 'DANTRA' above to get your engine speed.
Some of the responses on this thread recommend going to 3.32 or 2.76. Do the calculations. When I put me 46RH in, I was running 3.55 gears and at 60 mph I was only running 1800 rpm. I don't care what v8 you're using, none of them have any torque at that rpm unless you are running with a very small cam and a very light car. The engine has to have a decent amount of torque to keep the vehicle moving into a headwind. I know because my truck is like a 4/4 piece of plywood pushing air down the road. By the way my mileage with the 727 and 3.55 gears was 15 on the road. The mileage with 46RH and 3.55 gears was 13. Go figure. I think it's because of the low RPM's and less torque. I don't have enough mileage on the 3.73 ears to give an estimation yet. I just put the 3.73 gears in last fall.
