what to do next?

[sportrax stu]

i have a 400ex with a k&n air filter and a powercore4 s/o. im going to jet it, if i can figure out what the best kit is lol. i was just wondering wot i should do next.
any advice wud be good

[KeHall]

you prob colud have saved money if u bought ths filter and kit together K&N

[sportrax stu]

so is a k&n jet kit a good kit to get then? wot other mods do you think i should do? performance and appearence.

[KeHall]

If Iwas going toget a jet kit it would b a K&n u can get after market exhaust cam

[Snow]

How much are you looking to spend?

[sportrax stu]

sorry if this sounds stupid but whats an exhaust cam? £200/$400 is my budget really, or more if i really like something.

[Reaster00]

go to www.hotcamsinc.com for the exhast cam...thatll definetly help....also a high compression piston would be good.

[sportrax stu]

again this may sound stupi but on that site it says stage 1 for $185 each, do i just need one?! wheres a good place to get a high comp piston? ebay?!

[Reaster00]

yes you only need one...and depending on what else you plan to do you may want to go with a stage 2. I think the stage 3's would only be for a big bore kit...as for a high comp piston you could try www.wiseco.com im sure they make a variety of differernt comp pistons for the 400ex. Also a rev box would give you some extra power along with the piston and cams...id suggest www.biggunexhaust.com/product_info.php?cPath=198_199_200&products_id=618. That should meet you $400 buget and give you some very great power difference.

[sportrax stu]

thanks so much for your help, iv been on many quad forums in the u.k where i live and no one is nearly as helpful as you lot on here, thanks again
regards stu

[sportrax stu]

one last thing, before i stop hasstling you lol.
what compression piston would you recommend?

[KeHall]

you could just get the big bore kit it comes with the sleave piston ,rings ,gaskets wrist pin its around $240. 00

[sportrax stu]

i don't really want to bore my bike out. will have to bore it out often though if i put a hot cam in and a high comp piston?

[Reaster00]

a big bore isnt really going to hurt relaiabily that much as long as you get it done right. The three main big bores for the 400ex are a 416, 426, and 440. Anything above a 440 is pushing it. Its not going to cost much more to get the kit as a piston alone would be around $120 and you can get big bore that are a sleeve and piston kit for $240 then cams at $180 and the rev box still comes to around $400. But with the kit youd have to have the sleeve installed which im not sure a price on getting that done i would guess between 100-200. Im not sure what compression pistons they have for a 400ex that you would have to check the web site or do a search on this board under the 400ex section.

[sportrax stu]

cheers for ur help mate

[JOEX]

You can get a higher compression, stock bore piston. 10.8:1 is a common number. No need for a bore but the cylinder will need to be honed which a friendly shop may do for free or for a nominal charge. An aftermarket cam will be fine with the stock bore too if the whole 'package' works together.

From what i've read a well built stock or 416cc motor can produce very noticable HP, the higher compression and cam working together will provide the most gains.

[sportrax stu]

would i be able to fit an aftermarket cam without a high comp piston, or a high comp piston without a cam?
by doing these upgrades would it affect the reliability of the motor?

[rescue6]

First off your 400 EX only has one cam.Yess internal engine modifications effect reliability and there is a whole lot more to doing these mods than just the cam or just the High comp piston. If you are going to get a cam for a stock bore and stroke engine get a stage one from hotcams but to go stage two you need higher compression and a larger bore. Dont waist your time with a jet kit unless you have a 2005 or newer 400ex. And then that is just to get the D shaped pilot tool and the adjustable needle if not just go down and buy a 42 pilot jet and a 152,155,158 main jets and this should get you close to good

[sportrax stu]

so do you think getting a stage 1 hot cam and jet it then? would the motor be ok with the hotcam?!