Its not that you max out the dyno its self it is that you will start ro spin on it. The rollers are slippery and they tried to tell john that BHP stood for British horse power it actually means Brake Horse power. John those #s you put out were for the wheels not the engine so before your new combo you had 430 WHP.

If you could get them too put some traction on the rollers then you should try again. My mustang did the same thing spun its ass off. But he was in 3rd gear and at 3400 rpms it made 325 horses. Accordiing to the dynos here I was making 400 at the wheels .And that was with only 5 lbs of boost. And I think it cost 50 euro.