I just bought a 2003 Honda 400ex and already wanting to get some more power out of it. I tried running around on the internet but really couldnt find a honda quad forum that could help me out, any suggestions on where to go?
Yep, exriders.com or now known as atvriders.com I played with 400's a lot before getting more serious with MX and moving on to 450R's. I still have parts left actually haha. What are you looking to do, I know those motors inside and out. What kind of riding are you going to be doing?
Easy sell it and buy a 450r much easeir and proly cheaper in the long run! But i do have to say my buddy has one and on tight tecnial stuff like 1st gear he smokes me and all my other buddies 450's but i ride a yz250f bike...
i bought it for $1700 and it maybe has 20 hrs on it. took out to the dunes this weekend and was a ball with out paddles, it gives my friends 450 a run for his money on the dirt. it has a big gun slip on ( supposedly doesnt do anything i dont know) carb work, rejetted, and uni intake. im just wanting to dick around with a little, its fast now just want a little more power.
What i havenever seen any 400ex fully moded with a big bore kit be "fast" i was on my buddys 05 450 with just a slip on and raced my other budy with a high comp piston cam ported polished head full fmf exhaust and couple other little mods and he was so far behind afer maybe 150ft lol
Idk as far as forums or a whole lot about performance parts for those but i have a crf250r motorcycle that has about everything u can think of into it. The main place i would look for is Max power engines. Google that. And hotcams.com
i used to get on exriders once upon a time pretty good site,i have an 03 400ex and havnt been able to kill it yet.if you want big power sell the 400 and get a 450
i went out to the dunes this past weekend and tried to beat the hell out of this thing and it still is running strong so im gonna keep for a while. i heard from a couple people that the 440 kits are known to blow head gaskets. is this true?
my last mx quad right before the 450s got big was a 400ex, I talked to several engine builders and they all told me to stay away from the 440 kits.
I went about 416 on mine. I also ran a gutted white bros slip on with an FMF header pipe. got it jetted and had the head ported and polished and had a 5angle valve job done with a good set of valves. then threw a stage 2 cam and an after market coil on it.
In a straight shot i could run with most 450s that had been piped and jetted but couldnt touch one with a mild build.
the EX is a great quad just needs alot of head work to be fast.
headgasket issues with 400ex's are more from heat than anything. Guys run big pistons (thinner cylinder walls), and too high of compression without the proper fuel and the aluminum in the cylinder breaks down and the head studs pull out. GT Thunder has heavy duty headstuds and the right tap (roll form) to make it right. You would be fine with 11:1 compression pistons. Also note that almost all of the aftermarket pistons for 400ex's are actually designed for XR400's and for some reason Honda made the piston in the 400ex sit .040" down in the cylinder at TDC. So when you put in an advertised 11:1 piston, you're actually a lot less than that. When you start getting up in larger bores and higher compression than that, the rod becomes a concern. 12.5:1 and greater will need a heavy duty rod. Just some things to think about.
My suggestion from personal experience, get a stage 1 or stage 2 hotcam (new stage 2, not the old stage 2, which is now the stage 3) and an 11:1 stock bore piston, and use a cometic thin headgakset. I ran this setup on pump gas for over a year and beat the living snot out of it with no issues. You literally can't kill a mostly stock 400ex. If your cylinder needs to be bored, go to a 416 kit.
Are you running with air box lid on now? If so, take that off, the slip on and open air setup help a ton over stock too.
You're also going to want to put a CRF450 cam chain on that thing when you tear into it. 400ex's notoriously stretch cam chains. the funny thing is a stock cam chain runs over $100, but a CRF chain is about $25 from service honda. The CRF chain is the same chain a lot of places sell as a "heavy duty" cam chain for a LOT more money.
Any more questions just ask. I know quite a bit about these motors.
It's a 4 valve overhead cam mid-80s technology engine. Air/oil cooled. Even with a piston/cam pipe/filter combo, you wont be any match for just a piped/filtered 450R. I went through both of these machines from stock to full builds. The 450R is just worlds better. Once you've got all the motor work in the 400ex, then suspension is a huge MUST to keep the power to the ground.
BONE stock 450R... maybe. 04/05 450R's are insanely choked down from the factory...
What type of riding do you do?
A 400ex is probably one of the most reliable quads ever made though. If you're a trail rider, just keep the 400ex, do those simple mods I suggested and you'll have a really fun quad that will last a life time with minimal maintenance.
If you're racing MX every weekend, get rid of it and get the 450. Just my suggestions...
I've broke them, built them, rode them, raced them, you name it.
i dont know much whatsoever about a 400ex but i think it would take a high compression piston and probably a cam if not a little more just judging by the difference in displacement. Is a 400ex a high performance 4 stroke? I know my 250r is a high performance bike and air cooled 250's are also made which are two completely different classes of bikes. If the 400ex is not a high performance 4 stroke then u have a lot of work to do to get it to run like a 450. but like i said, i obviously dont know much about the 400ex
i basically just screw around on this quad. have never done mx and dont think i will for quite a while. i have only been to the dunes once but they are awesome and was planning on going back this weekend but plans got canceled.
If your just riding around for fun id keep the 400ex. My 450r can be quite testy sometimes and since i am OCD about maintenance the thing gets oil changes both engine and trans side every2-4 tanks of gas depending on how hard its ridden. Not to mention checking and adjusting valve clearances every 30 or so hours. In terms of performance, a pipe, jet kit, and filter on your 400 is pretty basic and runs reasonably well while still be stone cold reliable. But like others have said, its hard to beat the power of a 450.
It will be a great quad for you for trail riding and light duning. have buddies that are pretty quick on their 400exs that are modded. Awesome machines...
what i keep reading is stage II hot cam, 416 bore kit, and a 12.5:1 piston. Does this sound right? I want the bike to be as dependable as it is right now, just with a little more power. Im down here near Casa Grande, AZ and was wondering if anybody had any suggestions on shops. and maybe a general price to do all this
It seems like you should be able to adjust the timing without any cost. Just like an old gasser engine. Just twist the distributor. I know that can be done on my buddies 500cc motorcycle but it is about a 1980 model.
might check out this site. I have this brand of kit on my CRF250r and it has been doing great! may not be money you are willing to spend but my bike will flat out get up and go!
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