400ex engine mods..what to do?

[Bigg Pimpin]

I am going to pick up a '99 400ex this weekend and plan on doing some engine mods to it and am just not sure which way to go. I am thinking a 426 or 416 would be the best way to start as it just requires boring right? Then step into a 440 later on when it needs rebuilding. I am mostly going to be doing woods riding and I may get into GNCC later on so what's the best cam to use? I am also going to have some mild port work done and a slight shave to the head to help out there. I plan to stick with 11:1 comp. for better dependabiltiy. As far as bolt-ons I'll be running T-4 exhaust with K&N and no lid and eventually a Rev-box after I get used to my new found power. What all will I need parts wise to do the 426 or 416 besides the piston kit? Thanks

[Crazy400EX]

ya id like you know too cause im doing the same thing, my 99 has lost its power and i do woods rideing and getting into raceing.......someone help us

[04hmf400]

You will need head and base gaskets to go with the piston kit. When I put a motor together I use a hotcam stage 2 cam.

[honda_runner]

U should go with 216 bore, with a 12:1 piston, and a hotcams stage 1 or 2 cam. Stage 1 gives power low to mid, and stage 2 gives mid to high power. So stage 1 would be good for woods riding. With 12:1 u have to run racing gas to keep the temp down. So u might wanna run Wiscos 11:1 compression to run pump gas. Good luck

[Ryan]

Go with the 416. Your not gonna notice the difference between a 426 and a 416. Its safer going with the 416 anyways.

Don't bother getting a rev box unless you feel you hit the rev limiter to much. The 400ex doesn't make much power past the stock Rev limit.

If you run a 11:1 je piston, it would probably be better to mix a little race fuel with pump gas. I have the 10.8:1 je and notice it runs hot after awhile on 93 (pump).

An aftermarket cam would really wake up the motor. I personally would rather have the stage 2 hotcam. I have the stage one and would rather have a more agressive powerband.

With alot of these mods, I would suggest investing in a oversized oil cooler......

Good luck.

[sharkinthepool]

Personally I would go with the 426 kit. Yes, it requires boring of the stock sleeve, but go with the higher compression piston like a 12.5:1 and run 110 in it. Get the COPPER HEAD GASKET so you are not replacing it in 6 months to a year. Stage II cam and high performance valves and springs with a port and polish job.

And yes most def. a bigger oil tank preferably a Pingry with the cooling holes.

[AnotherSlow400]

Steve you have been on my quad, I would suggest either of the TC racing cams. The 926 would give you a great all around power for the woods riding you are getting into.

416 w/ 12.1 JE
TC Racing or Hot Cam
Ported Head
Sparks or LRD Full System ( I love my Yoshi but these seem to have a little advantage)

You might want to get new head studs and valve springs, or you could just have the head studs heli coiled.

A larger oil tank and upgraded clutch and a rev box depending on your gearing would finish this package nicely

[PHIL_B54]

dont forget the copper header gaskets, they deform and will leak if you re-use them.

being a 99' you might want to check out the valves and check the bottom end over good. im not sure i would feel comfortable 12:1 on a 99' original rod & bearings.

416 11:1 and a cam will do fine for power. if i were going to do it again, i would have put more money towards suspension. my $.02

[400-416EX]

I just built a 416 a few months ago, and wow what a difference it made. I went with a 10.8 je piston and run c12. I race mx. I got a full race port and polish. If you decide to go with the 416, I think you will be very happy with the results. Good luck building man.

[tc300ex56]

if your going to get it bored try to send it to tc they did a great job on my 300 bored it to a 330 and they broke it in too and get the tc pipe 4 low end power

[Bigg Pimpin]

Well after doing my research and listening to everyone's advice I think I've decided what to do. I'm going to do a 416 Wiseco 11:1 with the Hotcam stage 2, P&P head with new springs and valves, copper gaskets, Barnett Dirt digger clutch, swap the T-4 off my 250 for the FMF off the 400 to save some $$ for now, bigger oil tank, air scoops and if money permits have the carb reworked. Probably run a 50/50 mix of 93 and 110. :devil:

[fast4Exr]

do not use the pipe off of your 250. it will save you from a headache in the future

[Bigg Pimpin]

Why not? I believe everything is the same for the slip-on. I'm not going to try and booty fab anything.