I have Desk Top Dyno and the combinations are close enough to give you a good idea how a combination will work. The DD figure for peak hp on my 383 was 458 hp while the actual dyno figure was 450. That is slightly less that 1 per cent variance. Not bad when you figure there is a 5 per cent difference between different real world dynos (Superflow, Staska, Dynojet, etc.)