The O/D would drop the RPMs some more, but I am still wondering the RPM difference between that one and an A904 lockup. I will ask the guy you mentioned. We will be running 3.73s in the *** end, so an O/D might be better. Pros and cons though. A904 is straight bolt in. A500 i have to mod the crossmember.
The stock 904 lock up will drop engine rpm about 200 rpm but the gear set is a 2:45 low gear like a normal early 904. The A500 uses a low gear set with a 2:74 low gear.
I built my A998 lock up with wide ratio gear set to get best of both , low end torque with 2: 94 rear gears ( pulls out like 3:23) and has lock up in high gear at 1to 1 ratio.
Lon
