If my banshee is running right on target, just a little rich, would I have to rejet if I installed a Pro Design coolhead with 21 cc domes? I already have the FMF Gnarly pipes, reeds, reed spacers, boost bottle and the shee is running great. Will I notice much performance gain by adding a coolhead? Thanks for the info..

 

No I don't think you will have to rejet.

Yes, you will gain compression, creating more low-end power.

If you are just going for performance from the cool head, just get your stock head milled .40 or .50 for about $35. You will gain the exact same way, except looks and cooling (if they really do help cool)