I wanted a 450r but found a new 400ex for 4300 and couldn't resist. I now am looking to mod it up a little. I was looking at some pistons and wondering what kind of combinations you guys are using. I was considering a 416 wiesco 11:1 piston kit. Also considering a hot cam to throw in the deal. How much power will I gain with this setup. Also I was wondering if this may effect reliabilty any. thanks

 

yea i just got a new 06 400ex curious to hear what people say about between this and a 450r, stock for stock as well modded,, i know one thing was 400ex is air cooled and 450r is liquid.... but wanna hear what we all haveta say

 

If it's new, don't mess with the engine. (If it's not broken, don't fix it!) You will get years of reliable service out of that engine. Save it for years from now when you need a rebore.

You can open up the airbox lid (EHS Racing lid), put a UNI filter on it, and do a header and muffler, and net a nice increase in horsepower, without effecting the reliability of the engine.

 

I agree here all the way. I made a mistake by throwing a 440 kit on mine a month into it. It ran good but not how I thought. After a life of blown head gaskets and such, I put it away and purchased my new 450r. It's like a cadillac compared to my 400. I know it will get the best of you so if you're looking into building a motor, 416 with a weisco 11:1 piston and stg 2 hot cam.

I just recently rebuilt mine into a 426 11:1 and a white bro's desert cam and pro meg exhaust and it rips. I knew it was way faster than what it used to be and to my surprise, it runs away from my buddies 426 with a web cam and big gun. We did some pavement racing and I lost by one length to a stock '06 450r up to the top of 5th gear! I couldn't believe it. So we swapped and raced and swapped again, with the same results. First time to the dunes yesterday, and I did beat the '06 450r and a piped '05 and some kid's raced out 416 and slaughtered a 440. The 416 even beat the 440. This thing is a sleeper and I'm totally satisfied with the way it performs. I do have a vid cam and will have to get some action for you guys!

 

I agree with Reconranger. If it is new, I'd suggest freeing up the intake (better filter, remove the airbox lid) adding a slip on exhaust and rejetting the carb for those mods. You will get a nice increase.