[Tommy]

Speaking for myself, an occasional amatuer track guy, I doubt my lap times would vary much between a 400 HP small block and a 500 HP big block. In both cases, the driver (me) is a much greater limiting factor than the car.

Having said that, I'll mention that adding weight affects acceleration, deceleration, body roll, cornering G's, and many other performance dynamics. I wouldn't discount the importance of 100 extra pounds on a car driven by a skilled driver.