My car has only been run on a Mustang AWD dyno. They are known for being a heart breaker dyno. For the past 3 dyno sessions HP has stayed the same 391,389,390.9. TQ has moved, 470, 468, 494. The 494 tq that last pull was with my new DP's and 3rd cat and stock resonator delete. I try to dyno the car after every MOD and document what has worked on my SHO.
I would say the Dyno is pretty close. The math says is it takes 426 hp to the tire to move a 4560 lb vehicle a quarter mile at 110 mph. 426 to 391 is a difference of roughly 9 percent. I just want the damn 400 hp/500 tq dyno sheet. Maybe the MSD coils can get me there....if not it is still an upgrade and it costs me 70 bucks to get the car dyno'd.