performance suggestions

[sherman07]

I have a 2003 400 only aftermarket parts i have are, tie rods, nerf bars, and a fmf power core2 slip on exhaust. I have it completely apart because i wanted to paint my frame. I want to improve my performance when i put it back together. I do mostly trail raiding with it but most trails i ride have fields were i open it up full throttle and topped out.
If possible, I want to increase my top speed and my throttle response and acceleration in the lower gears also. i have considered the 11;1 wiesco kit, the bolt on and go on but i heard that it doesnt actually fit?? dont know if thats true or not, was told you had to bore out the bottom inorder for it to fit. anyways am looking to see what you all suggest as to what would be best for me to do. bike is going to look awesome when done want it to run even better then it looks.

[hocman123]

well the best thing to do if u are going to get a new piston is to bore the cylinder one size bigger and get a piston to match that way everything is fresh. u could get the stock bore piston and have the cylinder go bad 2 months later and would be boned.

also is u get the higher compression piston u should also get a stage 2 hot cam and the thing will fly

[quadmanw]

11:1 Wiseco Piston, 407 bore so you can bore it more. crf 450 timing chain, stage 1 or 2 cam, port and polish, port the inside of the headers, 450r carb, jetted correctly, uni filter.. Thats a good set up for what you are riding.. I just did that to mine.. havent got a chance to ride it yet. did the 416 instead of the 407 though.. wont make a huge difference. Thats a solid, reliable set up and most of the guys on here would agree

[sherman07]

Okay I just want to say this so it's clear. I am trying to do all the work myself. I'm not a mechanical genius but I do know a little bit. I'm not trying to split the cases on my motor. But I am comfortable with installing a big bore and stuff like that. I prefer things I can literally unbolt and bolt on I don't really want to be grinding anything out inside the motor to make a piston fit. I know a few people that had to fringe out ti get there kit to fit. So what exactly should I buy?? Thanks again for all the help and suggestions.

[dxcody]

Just keep in mind one thing that alot of guys overlook on here.. and some guys disagree with me BUT im going to offer my advice anyways.

Everyone on here says Bore it to a 407 then to a 416, 426.. etc.

Its cheaper to buy a new sleeve than it is to buy a new piston and rings every build.

You can reuse a piston 90% of the time.. they dont really go bad.

So why not get a 400ex standard bore, 11:1 piston then when it needs rebuilt again get a a $70 sleeve rather than getting your cylinder bored out, then next time it needs rebuilt buying another $150 piston...

I mean either way works, im not saying quadman is wrong by any means.. It just makes more since to me to buy a $70 sleeve and $25 new rings than a $150 new piston kit everytime you go to rebuild it..

[sherman07]

I was considering buying the 11:1 wiseco 440 bore kit its like 399I on eBay and it says all u have to division in bold ur old one and put on the new one. Do you guys think that's true??

[400man]

ive never had a cylinder resleeved, but im pretty sure theres a decent labor charge from most shops, usually around $100. resleveing a cylinder is not something the average guy can do in his garage if you want it to turn out right.

[quadmanw]

I didn't go with the sleeve Cody because I got a great deal on all of the parts I need and my buddy builds my motors so it's all cheap! I thought about the sleeve though! If I was doing it myself, I would probably sleeve it lol

[slightlybent47]

The problem with the ex is that if you gear it for top end you lose the bottom end and vice versa.
The ex has never been one for top end speed. There better set up for low end torque.
The 416 seems to be the best all around bore for the ex according to most of the post I’ve seen. I have a fully built 416 and it still lacks on the top end speed the 450’s have.

[sherman07]

Ok so would I be wrong by going with the 11:1 and boring it to a 440??
I had to help a buddy resleve his in his 300 between the two of us we have more tools then you could imagine lol. I just don't want to have to go threw that with mine.

[hocman123]

well if u go with a 440 u need to put a new sleeve in and i belive get the cylinder boed a little bigger to fit the bigger sleeve. so for the 440 u need to bore and resleve but if u go with a 416 u just need to get it bored

[slightlybent47]

Bear in mind that the thinner the cylinder gets the more heat becomes a factor. I’m no expert but from all I’ve read a well built 416 can run about as good or better then a 440. I’m told that if you stroke it you will get a stronger low end, but I don’t know what that does for the top end. A lot of the performance is in the head anyway, a good port job along with oversized valves and cam and a bigger carb and exhaust combo will wake it up nicely. Let that sucker breath!

[dxcody]

Originally posted by 400man
ive never had a cylinder resleeved, but im pretty sure theres a decent labor charge from most shops, usually around $100. resleveing a cylinder is not something the average guy can do in his garage if you want it to turn out right.

All you do is heat up the cylinder a little and the sleeve falls right out, and it has a lip it sets on in the cylinder so it really sets itself.

Put the new sleeve in the freezer for a few hours and it falls right into place. Its really simple actually.

It was just a thought!

[sherman07]

Ok so I'm starting to think that it's better to go with a 416. So if I do go with it what do I need to do to the Carb, do I need to re-jet

[JOHNDOE83]

Well I say go big or go home, if your gonna bore it go 440 it is faster then any 416 or 426, it doesnt lose any bottom or top end.

My 440 will easily hit 70mph in fourth gear "yes 4th gear" and keep up with or out run most modded 450s.

In all seriousness, any bore or compression is fine and will make huge improvements in power and speed and youll be happy with any choice you make.

You dont "need" to get a carb for a bored out motor but having a bigger carb will really make the best usage out of a modded motor, if you want a carb for throttle response "like if you MX' get a fcr, if you want a carb for the most power and good throttle response get a 05 450r carb.

If you bore or bore and carb your jets will need to be signifigantly bigger, I use a 220 main jet in mine.

[TheAwesomehonda]

Ok JW you say that you have a power core 2 exhaust isn't that for 2 stroke atvs?

[CJM]

The best setup for most is the following:
-407, 416 or 426 bore with an 11:1 piston
-Stage 2 hotcam
-Open airbox lid
-Good slip on exhaust
-GT Thunder heavy duty head studs
-Cometic brand Multi-layered steel (MLS) gaskets. The only gaskets I will run, they are the best. They should appear to be rubbery/metallic looking btw incase they got a pic.

That alone will keep you plenty happy in most cases. The bore size isnt such a huge factor unless you do a 440-is there more power in a larger bore, you bet. But its negligible in most cases unless you do the 440. The 407, 416 and 426 will all rev faster than the 440, the 440 however will have a bit more torque and topend.

All that being said, yes you will have to rejet it. You need to up the pilot jet to a 42 and buy a range of pilots from about 155-175 as a basis. Jetting isnt hard on the EX carb, its quite simple compared to other carbs.

I ran a 415, stage 2 hotcam and a open airbox for eons. Powers quite nice. Figure on a budget of at least 500 bucks. You need to bore the cylinder, get a piston and cam and a bunch of other misc parts. Also now is the time to replace the timing chain, chain tensioner and guides b/c usually they are worn.

[sherman07]

I don't know about the exhaust I picked it
up for. $50 from a guy and I saw him take of off a 400ex so ill find out when I put it on and start it, I know it will fit though.

I'm still undecided about which bore to go with I have a buddie that owns a ATV/dirtbike shop I'm going to get his opinion tomorrow. Thanks for the help everyone ill let you know what I decide& hopefully I get it back together soon lol

[dxcody]

Originally posted by sherman07
I don't know about the exhaust I picked it
up for. $50 from a guy and I saw him take of off a 400ex so ill find out when I put it on and start it, I know it will fit though.

I'm still undecided about which bore to go with I have a buddie that owns a ATV/dirtbike shop I'm going to get his opinion tomorrow. Thanks for the help everyone ill let you know what I decide& hopefully I get it back together soon lol


You dont HAVE to do what were saying. You can do whatever you want.. Just so you know.

BUT The setup that CJM and quadman said is what i put my money on due to it being AMAZING for the 400ex.

11:1 + stage 2 cam combo is just awesome, for the average everyday trail rider/ c class racer.

Anything after that is useless without suspension, because you cant go fast enough to realize to the power because your getting slammed around so much.

But like i said... Its YOUR choice.