Go Faster Bits pully set
 

I have got the full set of 3 pullys, but will i need different size belts when fitting these?

Are they underdrive?

i dont get underdrive pulles, shurley its not healthy for the car to have smaler pulleys than intended, or hav i missed a benoficial gain from fiting them?

When I bought my GFB pulley set brand new from Graham Goode they came with a belt which was smaller.

The reason for the smaller belt is the GFB crank pulley is smaller

i brought the pullys second hand, any idea on the size of the belt needed?

Your best bet is to put them on then use a piece of string to measure. Buy the nearest to the string you can get. Don't forget there's a fair bit of adjustment in the alternator pulley and aircon pulley.