I'm a skeptic. There's nothing wrong with saying "prove it". Thing is, the only way to prove a number produced on a dyno, is to accelerate a given mass, over a measured distance, with an accurate method of measuring the speed, and calculate how much power it takes to do it. Now there's nothing against any builder that uses a dyno. We all love the numbers and as the guy who puts it together, the dyno is a great way to see if things are doing what you expect. Problem is, at least in my opinion (skeptic's), is a dyno cell is not a chassis. Most are set up for ease of setup and removal. So they have their own water supplies, their own fuels sypply, their own big, long tube, smoothly bent headers dumping into big resonators or right out the wall, and a smooth bell that isused to measure the amount of airflow going into the engine (critical job). All of which make access and setup easy, all of which will skew the actual numbers to a degree. Dyno software and calibration can also be manipulated, or simply not really paid much attention to which can also skew the numbers. The fastest way to take 30-50 horsepower off a "500hp " engine is put it in a chassis. Where it has to pump it's own fuel, drive it's own water pump and alternator and maybe power steering and AC, run at 190°+ water temps, breath in through an air cleaner assembly, and push gasses out through smaller, more severely bent headers, 10' of pipes, and mufflers. The engine is still a great engine. But the realistic power level is not what the dyno showed. The performance at track will tell what that engine does in a real situation. Dynos are tools - not "truth".