I would have to add something to that in saying it's more often not changing of figures rather than incorrect setup of the dyno. Strap it down too loose and the wheel pulls up too far on to the front roller and bam, there's another 50hp. Air temp in the wrong place (by mistake) or just an inaccurate uncalabrated dyno.
Most times the dyno operator isn't doing it intentionally but mph on a drag strip has always been the best way to determine how accurate that power figure is.
That is completely true but.....
I think SAU has been around long enough to be able to make claim to being the absolute best source of information available in the world. It's really nice for people to share their passion and their joy here but at the same time, the figures MUST be open to scrutiny if they are more than expected or even lower for that matter. It's a public forum, people have different opinions and knowledge.
The worst thing for us is when we build/tune a car that has a specific setup based on what a mate has or what he read on a forum and it doesn't get the result they hoped for. Sometimes by a long shot!. They go down the road and get a higher reading and then suddenly tuner #1 is a bad tuner or their dyno reads 'low'. Get a print out from the other that says 550hp in your 33 GTST but only run 122mph
Well f**k low, f**k it in its arse. Go out and run it down the 1/4. I guarantee you'll run the mph that's accurate for the power and weight you have.....if you make it to the end in one piece hehe.
Reading, learning from others and pulling ones head in can often make you a smarter man, but only when you know what information to listen to and what information to hear.