Yeah - I was a little taken aback I must admit. I didn't necessarily expect the same figures, but not such a massive deviation either. Ambience will make some difference I agree, but doesn't explain the difference in RPM scaling. Tyre pressures were checked on both days; 34 PSI all round.
Nice pick-up on the RPM shut-off Phil, it seems bear relevance here...
I've just had an email from Bill who's been trying to figure this out and looking over the reports he seems to think the car may have originally been run in 5th gear with the dyno calibrated for 4th, affecting the load on the rollers and skewing the RPM scaling; which is calibrated as an offset against 3,000 RPM.
Craig made some comments about my car being very lively and wanting to jump off the rollers, with only a limited number of strapping points installed when the car went on in January, so it's possible the car _may_ have been run in 5th to calm the delivery of power. If that were the case then it would elucidate a correlation between these power curves.
I can't personally remember where exactly the car was strapped down (I *think* it was at the sides and on the front) but it was still pretty lively and looking back over the printouts and noticing the fact that the power run was backed off at what "appears" to be 6400 RPM it would make logical sense, i.e. the RPM ratio between 4th and 5th matches the deviation between the curves. If that is correct, then the 6400 RPM seen on the graph is in fact more likely ~7,400 - shifting the numbers significantly.
With everything else remaining constant between both sets of power runs (most notably boost) then there's no way you'd see the power delivery shifted in such a way in real terms.