Don't disagree on cat-backs; was responding to question on whether there were any dynos out there and the ones highlighted there showed modest gains, whether you believe them or not...what I did find interesting were some differences in areas under the curve at low rpms (and some losing power in this range), but again all within the margin of error. Of course anyone looking to add real hp, shouldn't be looking at cat-backs period.
Originally Posted by crabman
In order to prove out such a small gain manufacturers do very extensive dyno work under controlled conditions along with a careful analysis of the very comprehensive data they took simultaneously. Only in this way can they account for ambient temperature, humidity, intake temperature, coolant temperature, engine oil temperature, transmission temperature, differential temperature, air fuel ratio, differing moments of inertia, loading, dyno calibration, and many more factors.
When someone takes a set of cans, makes a few runs on a dyno, and says 2 or 3 hp increase the correct translation is that they were not able to prove out any increase whatsoever as the runs fell within normal run to run dyno variability. It is meaningless.