440 big bore

[400exman420]

looking to get a trx 400 to set up for hare scrambles and trail riding.. want to bore it out whats the best size for trails and racing? 416 426 or 440? and what other mods would make the bike fast for trails

[Drfat400ex]

A 440 is hard to do, unreliable, overheats and expensive. I also belive that the 426 and 440 will give you almost the same power gain. I personally would try 416 because riding the trails you wouldn't want it to be overheating and you don't want to be fixing things constantly. Other great trail mods would be slip-on, stage 1 hotcam, UNI filter, removed/aftermarket lid, yfz/450r front shocks, possible gearing change, with a big bore I think an aftermarket headpipe should do good, but don't bother with stock bore, and of course properly jetted (don't use dyno-jets).

[CJM]

A 440 is worth it, but you MUST jet it properly in order not to overheat it and you MUST get heavy duty head studs installed. If you dont do either of them kiss your topend goodbye.

What will win you races is speed, however without a good suspension the power is wasted bigtime. In the very least you need to remove the junk stock front shocks and swap honda 450r or yfz450r shocks on the front (click the link in my signature for more info) and have your rear shock setup for long travel.

From there you need mild engine work, higher compression piston, small overbore if you have some hours on the topend, while your in there its a good idea to replace the timing chain (if you have hours) with one off a 2002 crf 450r, check your chain guides and the tensioner. Then you should put in a stage 1 or 2 hotcam. Stage 1 will give you really nice torque, stage 2 is more mid to top with a decent amount of lowend.

Then you should throw the airbox lid away and put on an outerwears lid so it can breath. A good slip on is a must, motoworks, hmf, big gun, etc.

Then of course your gonna need tires, maxxis razr II fronts and razr rear is what the pros use. 21" fronts and 20" rears.

Hope you got alot of money, cause thats 2500 worth of parts EASY. if you dont have that much cash id do the suspension, cam and exhaust.

[jkosakowski]

416 with 11:1 or 12:1 compression and stage 2 cam and gtt head studs. And if you can a 450 carb and cometic gaskets.....i hear that's is an awesome setup.

[JOHNDOE83]

Originally posted by Drfat400ex
A 440 is hard to do, unreliable, overheats and expensive. I also belive that the 426 and 440 will give you almost the same power gain. I personally would try 416 because riding the trails you wouldn't want it to be overheating and you don't want to be fixing things constantly. Other great trail mods would be slip-on, stage 1 hotcam, UNI filter, removed/aftermarket lid, yfz/450r front shocks, possible gearing change, with a big bore I think an aftermarket headpipe should do good, but don't bother with stock bore, and of course properly jetted (don't use dyno-jets).



My 440 runs stock engine temps with no cooling mods and no HD studs, wasnt any more expensive then a 416 or 426.

[Drfat400ex]

Do you run race gas? All I ever hear about with most big bores is so many overheating troubles. They're more expensive if you're getting a shop to put them in as they're supposidly alot harder to do than most over bores.

[JOHNDOE83]

No I run pump gas, over heating big bores are usually because they are not jetted properly.

If I run any less then a 200 main jet I start to get noticeably hotter, 195 and less I start to pop when Im accelerating.

220 main is my EXs sweet spot.

[Drfat400ex]

Huh, good to know. Well let me rephrase my first reply. Make sure your jetting is spot on perfect OR ELSE you will have major overheating issues and reliability issues.

[CJM]

Gotta also remember John, your not rec riding. Its just being used for what 10 minutes at a clip?

[400exshop]

My 440 was great in the wood, like john said if you jet it right it will stay cool.

If you build it your self make sure you check the ring gap, this is something that alot of people dont do and the bike can over heat as well, and thats on any build not just big bores.

Just so you guys know, you can build any bike up to what ever size bike you like, but if you dont check your clearance, use all the good stuff, like matching it all up.

Pistion / bore, cam, pipe, head port and carb and put the bike on a dyno, then what good was the build ?

You need to put the bike on the dyno to make sure your air to fuel is spot on, that will keep the heat down and give you the best bang for your buck that you just spent on the build.

Thats just my 2 cent but what do I now, We just have to of the fastest 400ex in the usa.

[JOHNDOE83]

Originally posted by CJM
Gotta also remember John, your not rec riding. Its just being used for what 10 minutes at a clip?

No, this quad was a daily driver/ trail rider before it was a drag bike, it has alot of trail hours on that motor for sure.

[trxPOWER]

i have never had one problem with my 440, all ive done is jet it. You all say such bad things about the 440 and i doubt youve even owned one. Ive ridden that SOB in 95 degree weather for 3 hours on the trail and its been just fine.

[CJM]

Originally posted by JOHNDOE83
No, this quad was a daily driver/ trail rider before it was a drag bike, it has alot of trail hours on that motor for sure.

Forgot about that lol.

[400exshop]

Originally posted by trxPOWER
i have never had one problem with my 440, all ive done is jet it. You all say such bad things about the 440 and i doubt youve even owned one. Ive ridden that SOB in 95 degree weather for 3 hours on the trail and its been just fine.

10X what he said, And the one's that do have problumes, it becouse it was not jetted right or built right.