[B Parker]

My brother and I know that combo pretty well. My brother is the one responsible for the HP being at 287. And I now run a 74 vette with that same motor combo. As all of us know there are a ton of things that could cause your car to be off that much. I'm sure Charlie has you pretty close with the convertor. Michael Beard is right about the shift point. You can learn a lot from a play back tack. It would be easy just to say you are off HP but it would be nice to get more info on your engine. Any dyno numbers? Or any history on the motor? It sure sounds like you are off hp but you could have 4 or 5 things off a little that are costing you several tenths. The only reason at this point that I would change the gear ratio would be if I thought the ring and pinion was bad or set up wrong. The 538 may be faster in the end but if your 513 are set up right they will get you down the track a lot faster than your going. Make sure there not binding when the rear is warmed up. My Brother ran I/SA for the first couple of years in that combo and had 514 in the rear and went pretty fast with a lot less hp than he ended up with. Good luck