2 inch exhaust??

Unless you are racing an looking for every .1 second you can find the butt dyno makes perfect sense to gage changes. The generally accepted number is 3-4 HP to be noticeable by your butt in the car.

As far as my car having 370 HP it's never been on a dyno so the number is an approximation and that is why I prefix it with ~ , that means approximately by the way.

I came to this number by the fact that the car with me in it weights 3650 lbs give or take depending on how much gas is in the tank and the fact that it runs between 102-103 mph trap speeds in the 1/4. I have also run the build through several dyno software packages that predict the engine will make ~390 HP so I feel pretty comfortable that the 370 number is reasonably accurate.

When I first installed the 360 I hooked the headers up to the 2 1/4" compression bent H-pipe system that had been behind the built \6. I ran it that way for several thousand miles before swapping in a 2 1/2" compression bent x-pipe system. I did not detect any change in the power by the butt dyno. This system was in the car until this past winter when I swapped in a mandrel bent 2 1/2" x-pipe system. I didn't make this change for power, I did it to get more accurately bent pipes that would not interfere with the shocks. Again no noticeable change in power.

A few years back one of the mopar rags took a 340 Challenger that had headers hooked to an other wise stock 2 14" exhaust system and base lined it on a chassis dyno. The first change was to swap out the mufflers for performance mufflers (If I recall they were Dynomax Turbos) and the picked up about 7 HP, a change easily detected by the butt dyno. They then swapped in a 2 1/2" system using the same model muffler and got another 4 HP right a the edge of whether you will detect it by your butt dyno. They then swapped in a 3" system with the same model muffler and only got more noise with zero additional power.

This dyno testing between the 2 1/4" and 2 1/2" systems pretty well aligns with my experiences so I figure my butt dyno is reasonably able to detect the generally accepted 3-4 HP number.

You can believe my comments or not it's your business but it helps no one to dump on some ones actual experience when you have offered ZERO evidence to the contrary.