Hard proof for me would be the car dyno'd each time in the same relative conditions. Same dyno and temp / humidity being pretty close for all runs compared.
Dyno'd stock with at least three pulls. Better if done more than once at a different session to confirm numbers.
Then dyno'd again after each change is made to see any difference(s) from the alteration. Also prefer the car get dyno'd at least a few weeks after the mods to confirm the Delta wasn't temporary and the car has readjusted itself after driving cycles.
The type of dyno isn't really as important as using the same dyno for the comparison. The Delta is what should be telling.
Yeah the internet can be a bitch, which is part of the reason I like to see as conclusive of proof as possible.
Luckily for me I've had the car dyno'd several times on the same machine and know my numbers are pretty solid under the same conditions. So any changes that do occur, like the dealership muckin up a repair and causing a HP loss (cough,cough), can be proven to be reliable.
