i was running 4.56 with a 431 bbc 2500lbs turbo 350 trans coan 8in. 5000 stall dana 60 rear. car went 9.50 traps 7000rpm went to 4.88 traps 7200 ran 9.30et built a 481bbc went back to the 4.56 traps 7600 9.13 et spun a bearing and built a 511 bbc 4.56 gear put in a pglide same converter traps 7900rpm 8.80et going to a 4.10 gear this year to much rpm for me car has lots of tourqe big wheel stands. was told less gear will help there to. hope this helps some. good luck!