Your local hobby shop is right . . . A deflector will in fact reduce your power.

The reason your heli had less power AFTER you removed your deflector is because the high mixture needle needed to be re-set.

So does it have more power with or with out it?

Sorry for the confusion, I adjusted my statement above.

so if your engine has plenty of power with a deflector... do you need to remove it?

I put a 90 size on my 50 and its fine... still only using 85% throttle on a climb out or it massively overspeeds... with +10 on the top!

Beauty is the model stays a lot cleaner...

I have a Raptor v1 30 with a Westin Tuned Pipe. I initially put an exhaust deflector on my raptor to minimize the cleanup as much as possible.

After putting the deflector on, the mixture was off and after re-setting the mixture, there was a loss of power. (not much, but when you are flyiing a 30, it is enough of a change to make you think twice about the hassle of cleanup)

The deflector was extremely close to the ground (within 1/2") and so I decided to remove it. The nice thing about my Westin Pipe is that the exhaust port points down towards the ground minimizing cleanup.

If you are running a 60, or 90, then power should not be an issue.

if you add a defelctor to a tuned pipe then you are gonna slightly affect the tuned length, but not by a massive amount, yes it will reduce power slightly (otherwise weston would have made the outlet longer) but try using an outlet that is much larger, ie designed for a 60-90 and then the effect is much less...