sounds like he's got the torque motor.

Neoslan, yes, going to 48v would increase your speed to about 22 or 23 mph but I'd suggest maybe buying a different motor. Like maybe a 2805 Nine continent.
http://ebikes.ca/store/photos/M2805FD20.jpg

Do you have lots of hills in your area? If so, then the 2805 might be a bad idea. The 2805 is a speed motor. It has comparable speed to the 5303 crystalyte in a 26" rim. It only comes in a 20" rim at ebikes.ca so you'd have to spend $80 and get it put in a 26" rim if you wanted to do that.

What kind of speed are you looking for?