I put a 43 tooth rear on with my stock chain and front sprocket. It barely fit the PRM skid without shimming it. You should replace your swing skids, one bent rotor and it will pay for itself.
A slip on pipe, trim the snorkle flaps and rejet will probably get you what you want from the engine.

 

I don't understand what you mean no lowend? My Raptor had tons of "Lowend" even in stock form. It would jack the front end off the ground in any situation in 1st or second gear, 3rd just as easy after pipe and, jets. Lowend in my eyes is the power at low rev range (which the big 660 bore is best at) and, i think you are confused on what it is and, what it should have.

If your expecting a sudden burst of power i think your wishing for a 2 stroke (and, they hit hard mid to top but, in a big burst). 4 strokes power and, torque curves are more wide spread, flatter and, controlable.

Torque is what gets you out of " the Hole". if your raptor isn't already hard to launch with out the front wheels in the air maybe you have 2 duds?

 

Wrong thing to do if you are looking for low end power. By opening it up you are killing the velocity of the air. Nice for top end power but it will kill off the bottom end. For bottom end, you need high velocity air flow, and that means small carb and small intake tract. For max power, you want max flow.
If you really want to get crazy you could advance the cams a touch, but I could not imagine you would have to do this. Like the others said, I would just gear it.

 

I agree with DoctorTurbo. I was going to ask where he got his handle but then someone
would want to know where I got mine, bopeep. It's a long story and has to do with real
live sheep and everything!

So I've ordered two sets of sprokets, a 12 tooth front, and a 42 tooth rear. Here are the
possible final gear ratio's for all possible cominations:

40/13 = 3.08 (stock configuration)
40/12 = 3.33
42/13 = 3.23
42/12 = 3.50

First, I'll change just the fronts and go for a ride. As 3.33 is slightly over half of the spread,
and it should tell us if this is enough or if we need to drop slightly to 3.23 or go for the works
at 3.50. BTW, the service guy in our local Yamaha shop thinks I'm nut's for doing this in the
first place. Ok, one guy's opinion, but we need to do something before we start burning out
our clutches.

bopeep (a real "sheep" kind of guy)