I am putting a beefy 360 and maybe a 3.23 rear gear in my duster and was wondering which would be the better way to go as far as transmissions a 4 speed or 4 speed OD?
One of the main problems with the OD is it was built sloppy, they called it a floating cluster gear? The other is the Aluminum main case, now even more at risk because the countershaft is now loose in the main case bores. Now add ATF for gear lube because you want to reduce friction... If you replace the aluminum main case with a cast iron main case, also replace the OD countershaft with the standard countershaft, and add SAE 90 gear oil, things tighten up pretty nice. As others have said above, it is best to look at the OD as a 3 speed with an overdrive. If you want to race, do it with 3 gears and save the OD for the highway. With a relatively high torque, lower RPM small block the OD should be perfect. With 3.91 gears and a .73 OD your final ratio becomes 2.85. With 3.55 gears and a .73 OD your final ratio becomes 2.59. With 3.23 gears and a .73 OD your final ratio becomes 2.36. For long road trips we used to swap in 2.76 gears without the OD for mpg. I'm running a regular cast iron main case OD in my 66 Formula S with 3.91 gears and it runs pretty sweet. 3.09 x 3.91 = 12.08 torque multiplication in first gear, with a 2.85 final ratio.
