First, the dyno is great for working with the engine on the stand for tuning and parts testing. But not so much as comparison as Dyno's vary. Second, the dyno brake cannot simulate all that goes into a car going down the track. Like wind resistance (as the car goes faster), change in gearing as the car shifts, and the workload changes. This is why we see dyno'd 400 hp motors go 12.8's in a 3200 lbs car without wheel spin. I can tell ya, it don't take anywhere near 400 hp to run that number.