Quote:

YOu need to figure out what is the lowest RPM your car can pull, and keep in ming that if the engine is lugging you may get worse fuel mileage than spinning it at higher RPM.



Yup, and I hope anyone smart enough to do their own 6-sp install would have the foresight to take into consideration how low of a rpm you can really run your engine before you start dropping below your efficiency zone. Camshaft and carb type or efi will make the difference in this case. I think you would need a 4.10 or numerically higher gear with a .5x 6th gear.


Also, I believe the OEM T-56's in the gto, cadiallac cts-v and the camarobirds had a .57 6th gear ratio.