Would it be worth my while to bore my '03 400ex to 426 for $135, not including shipping/handling on the motor? If so, should I pipe it first, and then wait a while to bore it..

 

Definitely pipe and filter it first. The stock set-up chokes the stock bore motor, imagine how much it will choke up a big bore motor!

 

I already have a k&n filter..... I was thinking of putting a WB E series on it a the begining of this summer and sending off the motore to be bored in September.. Would that be a better idea than boring it, and then considering a pipe?

 

i would probably do the engine work then get a pipe. it wouldn't really matter and i say you might as well get the engine work done with. by the way, when you get the piston, add a cam too. this will greatly improve the performance of the bike.

 

I just made my wifes 400 a 426. It is an 11:1 wiseco piston. The quad was already piped and jetted with a K&N. It gained alot of lowend power. It now makes the front light in 3rd like it did in 2nd. I don't think it is any "faster" but it works alot better in the woods now. If we would have put a cam in it it with head work it would have been faster, but she wasn't wanting to put $$ into it.

 

So you think I'd be safe doing the engine work before piping it?? Or just to be safe put maybe a WB E series slip-on on it first... Also how much $$ would a new cam be?

 

It would be safe to put a piston in without a pipe, but would be a waste. It would run better with a muffler insalled.

You can buy a hotcam for about $100. If you want a better cam you will spend about $250 for a Web with hardened rockers.

 

yes, no damage or anything will be done when running a stock pipe. i can tell you a cam/pistoned bike will outrun a piped and jetted one. just rejet either way. by the way, i would go with a full system. we had massive gains from a full hmf over our white brothers slip on. it almost felt like we got the power gain from a cam and piston all over again.

 

A kit should be the last thing you should do. The stock pipe is going to be to restricted. Get full exhaust and a jet kit before you put a cam and piston in. The 426 is a good kit but not as reliable as a 416. The 416 will show a lot more performance than a 426. I have a 416 and it can beat 426’s.

 

this is nonsense. i will guarantee you a 400ex with a cam and higher compression piston in with jetting will beat any stock 400ex with a pipe, filter, and jets. also, a 416 is not faster than a 426. can it be? well of course. a stock bore high compression 400ex could easily smoke a 440 or vice versa. it all depends on the build up. my 426 beats the average 416's that i have raced by about 5 bike lengths when dragging. i am not saying i will beat every 416 but the ones i have raced, this is the outcome. it all depends on how each motor was built. a 416 could easily smoke me if the compression was high enough and the motor was more decked out with mods than mine was. the only difference between the 416's and the 426's is the 426 is approximately 1mm larger. it also weighs a few grams more but also has a little higher compression than the equivalent 416. yes, you can get any compression want but the normal 416's are 10.8:1 where the 426's are 11:1 or 11.1:1.