What Can I Do For More Power?

[cheater13]

I'm still lookin to get some more power out of my ol 400ex even though it has a good bit. :devil: Everything that is done to it is in my sig, but what else could i do to it while keeping it at the stock bore? I wanna try to get as much power out of it as i can before the only choice left is to bore it.

Any recommendations?

[TacicalRedneck]

I don't think the FMF is doing much good ;)

[JOHNDOE83]

You could bypass the oil catch that goes into your airbox and you could also remove your airbox.

All slipon's are the same so your not losing any power, but if you wanted to gain a lil extra you can hollow out your slipon and grind your header welds if you dont mind it getting a lil louder.

With your mod's you could slightly benefit from a rev box also, I reccomend a white bros.

Edited > HA, I saw that you have a power bomb after I posted this, you dont need to grind your welds:blah:

[01boneless]

oversize valve and if u have a ton of money get a stroker crank

[Jayskee]

Maybe change out the cam.. If you start throwing too much money into you might kick yourself later. I'm seeing banshee's on eBay going for 4k done up. And I keep asking myself why am I redoing this old 400... Lol

[cheater13]

TacicalRedneck: Haha i would get a pro circuit or motoworks but i like the sound of my ol FMF. Sounds mightly loud :D

John: I would remove the airbox but i still like riding it around fields and trails and all. And dust and stuff gets in there fast how it is with the open lid.. I was wandering about the welds hahaha. But how much does one of those rev boxes cost?

boneless: I was thinking of doing my valves and getting a different crank. How much does that run?

Jayskee: What could i change the cam to? I heard of custom cams but i heard they were alot of money too.

[01boneless]

valves are like 100.00 then ull need heavier springs 150.00 and the valve job 150-300. crank is like 300-450 depending were you get them these are all estiments i havent looked at prices latley but thats close to what it all runs.

[jman7290]

Get one of the degree keys that fellow member on this site Wheelie sells, lighten your flywheel, rev box, gearing, stage 1 cam for more low end if that is what you are looking for.

[Drfat400ex]

Originally posted by jman7290
Get one of the degree keys that fellow member on this site Wheelie sells, lighten your flywheel, rev box, gearing, stage 1 cam for more low end if that is what you are looking for. I don't think you'd want to go messing with your spark timing with 12.5:1 compression, lightening the flywheel won't give you anymore power but as far as I'm informed it does let you speed up a lot faster, so really no added power but acceleration. I hear they retarded the ignition 4 or 6 degrees from the xr400 to the 400ex, and a lot of people put up the argument why not put it back to how it was? Well I suppose they changed it for a good reason. Anyways all I could think of was already said on here.

[chronicsmoke]

Who ported your head?

You could be leaving a few HP on the table if it was just a generic clean up sort of job.. Other than that you'll have to start boring, stroking or both. Lighten the flywheel if you want it to rev faster, but you'll lose some low end chugging capabilities..

[cheater13]

I wish i could multiquote this stuff...

boneless: That's a good chunk of money for that kind of stuff. Is there any specific brand that is good? I heard of Kibblewhite valves but haven't done alot of research on them. And the only different crank setups i heard of was hotrod and wiseco. What websites could i get this stuff off of? I normally look on ebay, but i don't know if that's the parts i'm looking for.

jman: I would but i heard them timing keys are for lightly modded or stock compresssion engines, but i could be wrong. And I don't really want to get stage 1, because i already have a stage 2 hotcam and it has an all-around power i think.

Drfat: I was thinking of doing the flywheel, but i'm unsure of it still..

chronic: A guy that worked for Elite Performance Racing i'm pretty sure. He said he really spent time on port and polishing it so i'm taking his word for it.


Will all this take the reliability away from it? I want a good bit of power, but i don't want to take away my normal riding capabilities and the reliability of the machine.




Also, isn't the cdi box on the 400ex like a xr250r? Would getting one of those cdi boxes be cheaper than getting a white brothers one?

[chronicsmoke]

if it's built right a stroker or big bore setup will be reliable..

My 400 has been a 426 since around 2005 and is still going strong..

[cheater13]

Alright, cool. But where would i look at these kind of parts at? Like the crank, valves, and cdi? I tried searching them on the internet and ebay just comes up.

[thebig450es]

I went with the 7mm stroker and a 87mm bore with 12.5:1 compression. Its holding up great, check out GT Thunder

[JOHNDOE83]

Originally posted by cheater13
Alright, cool. But where would i look at these kind of parts at? Like the crank, valves, and cdi? I tried searching them on the internet and ebay just comes up.

Ebay is a good place to buy stuff easily and inexpensively.

www.rockymountainatv.com is a good place also.

[Quinn4]

Don't want to get flamed here or anything, but just curious why dump so much money into a 400ex when 450r's and yfz's can be found for like 2k and your already so much further ahead. To each their own don't get me wrong I'm just curious.

[ish416]

You are done making easy power if what is in your sig is correct.

If you go with a cdi, they advance the timing a bit at certain rpms which will likely result in some form of engine failure with your 12.5:1 piston. As there will just be to much heat/stress.

Even a bigger bore won't get you more than maybe a horsepower or two at that same compression.

Either bore and stroke it to a 440 or get a different quad. Power from this point is going to be costly for a very minimal gain.

If you want to make more power, check out Powroll's 440cc BORE & STROKE COMBO. (http://www.powroll.com/P_HONDA_TRX400EX.htm)

Also, are you sure that the piston you are using is a 12.5:1 Wiseco standard bore piston? Wiseco's catalog only goes to 11:1 standard bore and 12.5:1 on their 440 kit. JE offers a 12:1 standard bore piston. I only ask because I have never seen a std bore EX piston over 12:1.

[cheater13]

Alright thanks tons everyone!

And I'm about 100% sure it's 12.5:1. I can't really check but that's what the guy from elite performance racing said.

And one of my buddies said he would give me a Bit Gun Cdi for my 400ex for free. Should I out it on? I was thinking it might help me with my 2nd gear launches being able to wind it alittle more.

And yeah, I wouldn't put a timing key in it cause I only heard they were good for slightly modified engines.

[ish416]

Most of the cdi's advance the timing just like a timing key would. So I wouldn't recommend it, I have ran a WB cdi and the only difference I noticed was that it was harder to start in cold weather.

As far as your launches, short shifting an EX works best. These engines stop making power around 7500 - 8000 rpm. Spinning the engine past that doesn't make you accelerate faster.