This is open headers with 3" collectors vs 3" X-pipes ending with Dynomax Ultraflo or bullet mufflers ending at the rear axle.
In my particular 360 race only application, not only did it help ET/MPH a bit, but the now more efficient exhaust provided a bit more performance with jets 2 #'s leaner. I'm talking about hundredths. not tenths in ET. But it depends how close to optimum your jetting is to begin with. Weight was kept the same because the 55-60 lbs of X-pipe.muffler weight was removed from elsewhere in the car.
