Possible engine mods 400x
 

Hello everyone, Im new to the forum and looking for some ideas. I have a 400x and was wanting a little more bottom end and mid range power. My riding is trail riding and hill climbs. Here is what I currently have done, 450r front shocks, uni filter, ehs lid, lexx slip on, and rejetted. I was thinking about a hotcam stage 1 or 2, but not really knowing how far I want to tear into the engine and lose reliability. Will the cam wake up the 400 at all? Any ideas or suggestions? 416 bore?
Thanks

stage one cam will be more aggressive for the bottom end and stage 2 is for mid range. Im running stage 2 and its pretty good. Boring it wont really do to much unless you are planning on doing other mods. you can always get a higher comp. piston like a 11:1. If your looking for bottom end and mid your best if probably to let it breathe as much as possible and also look into a 04-05 450r carb.

Is there a lot of mods that have to be done to get that carb to fit? Do you think a 450r carb and stage one cam would make a noticeable difference in power?

FYI: your motor is plenty tough. Heavily modded 400's seem to last forever with the exception of going too big of bore (440).
My daughter raced a 416cc. Never a problem.:)

Would I see power gains and would it be worth it if I added a 11:1 piston, mild P+P, and stage 1 cam with the stock bore?

Yes!
Bore don't mean that much.
I'd recommend calling reputable motor builders and get their opinions and prices.
Baldwin Motorsports
Hetrick Racing
TC Racing Engines
Mickey Dulap's "Four Stroke Tech".
GT Thunder
And the ever famous and undisputed 4 stroke king~ Curtis Sparks!
All have built way many and can send you a complete kit that can be bolted and go.
There are tons of other shops but these all are well known and very reputable.
No offence to anyone I didn't mention.

The biggest boost in bottom end is a big bore kit. I have a 500cc on my 400ex and it has gobs of low end. To feel the effects on the top end you need to open it up..bigger carb full exhaust etc. But for trail riding its a rocket! also its a 11:1 compression ratio. its ultra reliable and uses pump gas and no over heating