it's a gearing change so to speak.

A dyno usually doesn't show any power change, if you take into account the error margin on the readings.

Dyno's are a good general tuning aid. The 'look at my power graph' manner that most people go and get the tuned based on, overlooks the best a dyno really has to offer.

For instance you can 'time' the accelleration across the graph to determine intertia or gearing benifits in comparison. It's a very handy thing to do, it tells you more about how fast your car is than the power curve.Although it still doesn't account for everything (like aerodynamics /weight etc.) Most people have no clue about this fact including 99% of workshops who own a dyno (perhaps I'm being harsh). Somewhere in the whole dyno fad people forgot what they wanted more power 'for'.

Next time you go to tune your car on a dyno get a time axis on some of those graphs. You can see what all that lovely extra power is really doing or check out the gains from the new light weight flywheel or carbon fibre tail shaft. You can even see the reason why fattening up the power curve at the expense of a little top end is a good move, especially when you have poor ratio spacing in your gear box.