If you dont mind spending alot of money the Sparks kits are supposed to be great. I already have the X-4 exhaust, but have already scheduled for him to build me a 416. Unfortunately, it looks like now I have to get the new X-6 exhaust cause it flows even better.

Sparks used one of his 416's in the legends race and it did pretty well with the 250r's and the YZ400 quad. So I am pretty excited to get mine done this october.

Curtis has all the info on his website for the 416, 440, and 465 kits. With mention of a possible 505 kit. So I guess the 440 is no longer the big boy on the block.

Adam Smith
99 400EX

Sparks exhaust, Uni air, CT Rev, DG nerfs, renthal bars, Motion Pro twist, Pro Design kill, and case saver, Denton +2 a-arms, Lonestar steering stem, anti fade locknut, and bearing carrier, Durablue eliminator 2+2, Fastline brake lines frt & rear, TCS Zips frt. Sparks 416 kit coming in October

 

I have a 416 built for MX and I love the power. All my specific mods are listed in my signature. A friend of mine at the races has a 440. They are NOT the hot setup for MX. They build a lot of torque but not near as much revs as my 416, which is a disadvantage in mx. Plus my friend with the 440 blows headgaskets constantly. He said he wishes he had got the 416 now. I also recommend Curtis Sparks. I have his x-4 pipe and it flows like no other pipe I've seen. Tom Miller also gave me a lot of my parts.