https://www.youtube.com/watch?v=_PVXvHkr-Vs They retest this exhaust on a 350 hp small block in episode 17. Virtually no difference in power between 2.5 and 3 in that test. 3 inch was louder of course. Unfortunately, I can't provide a free link to that episode as it is only available on Motor Trend On Demand until next month.