re ' ' big block exhaust question dick whittington the most common supposition to this mystery is that car manufacturers had started to play games with their horsepower ratings thus playing mind games with uncle sam and the insurance companies the exhaust did a lot to lower the horsepower rating for the solid lifter big blocks example l with dyno headers made anywhere from to horsepower with inch exhaust a measly horsepower another clue from this era was the rating of engine horsepower at a lower rpm than the red line nothing in writing that can be proved but this is what i have always been told