From the late sixties on, the carbs and distributors were calibrated with emissions in mind. It killed hp. Our old 427 was a little disappointing at first. Once the carb and distributor were sorted out, it was a whole different animal. This graph shows just how much improvement can be made with getting the carb right, and this is a mild engine. Quite a bit of hp for not a lot of money spent and the car will drive a lot smoother too.