O.k get this...
Me and my brother raced our 450 foremans. From a third gear start he was quicker off the line but then I started to catch him after about fourth and fifth gear.

This is the thing,

His is a stock 2004 450 with 26" Mudlites.

Mine is a 2003 with 447cc (bored out) with 9.5:1 compression Wiseco piston (stock is 8.5), also I have a clutch kit (engages 300 rpm higher then stock) and I have 25" bearclaws. Stock air filter, exhaust, jetting. I did not rejet after the engine work.

All things say I should smoke him, What the hell?

Can anyone explain to me what I can do to increase power?

 

Increase power? Sell your quad and buy a different one. You're really barking up the wrong tree trying to extract speed out of a 450 Foreman. These machines are pure utility/mud and built to last. This is apparent just from the low compression ratio: simple, more tame engines also mean more reliable engines. You may be more interested in either a Honda sport quad or a Suzuki utility like a Vinson.

 

Hey, if its the quad you own and its paid for, go mad with the mods. You can get a nig bore kit to 473, which is close to what the new foreman 500 is. Since you have already done this engine work, you may not want to go that route. With your setup stick on a K&N filter with an outerwear, a second snorkle (on the opposite side of the airbox from the stock one), a better silencer and see how that goes. With those mods combined with what you have you'll want to rejet the carb. With that compression, maybe you should run at least mid grade gas, maybe supreme to help prevent detenation.

For racing, get a set of light aluminum wheels, and the lightest 2 ply tires you can find, keep the heavy mud tires for the mud.

If you want to smoke him, pick up a NO2 Kit, reliability will go out the window on that one though.

Highlifter has alot of nice gear for these quads.

 

I find it hard to believe you didnt win. Those tires should have held him back.
Have you tried a second gear start, or does it seem to pull 3rd from a standstill ok?
Your gonna have to free up the breathing to get better performance, intake and exhaust, and then rejet to take advantage of the breathing.
If that doesnt do it...a cam would be the next choice.