Need Help on Making the Fastest/Stock Looking 400ex!

[cheater13]

Well, this Winter i want to get my 400ex worked on again. I drag race it and field ride it with little trails, but that's about it.

I want to get everything i can do to it done to make it the fastest it can be. All inside-the-engine work. I need to keep it stock looking so i can enter in the stock and beginner class in my drag races.

But remember, it needs to still be field-riding worthy and reliable.

Everyone at the recent drags though it was a 450 since i was making a killing on the drags. My best was a 4.9 this year compared to my 5.1 last year, beating alot of 450rs, yfz450s, and some Raptor 660s.

There was a monster 2 stroke bike killing everything holding a wheelie down the track. Along with a Can Am Renegade and Artic Cat 1000, but they were in other classes thank god.

So any suggestions on some good builders i could ship my cylinder to? I need to ship my head to gtthunder still because i snapped my stock head studs again.

I heard fourstrocktech is pretty good? I just dont want to spend a grand or so on this and it breaking all the time and not being reliable for my daily field ripper.

Here's some pictures to keep you all entertained:





I just had the underglow on that blue cause it looked cool. It has many colors+strobe effects to choose from.

[cheater13]

Wow, so much help! Thanks guys!

[400man]

patience young grasshoppa......high compression, like 12:1, bore size doesn't matter too much, aggressive topend cam with hardend rockers and stiffer valve springs, ported head, 450r carb or yfz450 fcr carb,, xr250 dirt bike cdi box (higher rev limit), stroker crank if you want to split the cases, full exhaust with shorty silencer, but don't "hollow" it out.

[DragonGunner]

You have already done most everything....can always experiment with different gearing, a longer swinger could help keep the front down better. Higher compression with race fuel, or bore to a 407 or 416 with higher compression.

[JOHNDOE83]

I never got a trophy

[JOHNDOE83]

If you wanna take another few tenths off your time, strut the front and back then remove your air shrouds, thats good for about 40lbs off the stock weight of the quad.

[cheater13]

patience young grasshoppa......high compression, like 12:1, bore size doesn't matter too much, aggressive topend cam with hardend rockers and stiffer valve springs, ported head, 450r carb or yfz450 fcr carb,, xr250 dirt bike cdi box (higher rev limit), stroker crank if you want to split the cases, full exhaust with shorty silencer, but don't "hollow" it out.

I have most of that done besides bigger valves, different springs, and I guess I could go to 12:1 later on as long as I can run 93 in it for field riding. I'll get that rev box sometime here because I heard that's similar to white brothers. I just can't find any more white brother ones. Don't really wanna stroker crank yet until something happens to mine though.

You have already done most everything....can always experiment with different gearing, a longer swinger could help keep the front down better. Higher compression with race fuel, or bore to a 407 or 416 with higher compression.

I think I got the perfect gearing for 250-275 feet (13 front, 40 rear), but I don't think I wanna worry with a swinger and having to switch it out all the time. The front stays flat on the ground how it is when I take off. I run 112 octane in it for racing only.

I never got a trophy

Me either! I just happened to get one for the barrel racing because I'm good at that!

[Zakradu398]

All you really have left is a more agressive cam (webcam) which requires rockers and springs I believe and bigger valves without tearing into the bottom end. I highly doubt you can run 12:1 on pump (93) but I have seen it done... Best bet is weight reduction.

[cheater13]

How do I know what kind of webcam to order? And what about boring to a 416 or 427?

Would doing the rockers/springs/bigger valves decrease the reliability? Since I don't have a shop nearby, who could I get to do this?

For my next drags, i'm getting them Douglas .125s instead of my regular stock rims. That should help some. Plus, I guess i'm going to get an HMF slip on so I can retire the old FMF Titanium. I'm going to make the FMF into a shorty and see how it does when I get the HMF so I can compare.

[Chukkinsod]

If you are going to drag an ex....light = fast. take off everything. You can leave the plastic but may want to drag cut. If you run struts in the front and back and remove the front brakes...huge weight savings. Also run the 125s like you stated and no front bumper. The front end WILL come up quicker the lighter you make it...so you will have to play with gearing and/or slip the clutch out of the hole or run a wheelie bar. Rev box does not produce additional power but it will allow it to not hit the limiter as quick (shifts). Leave on both bars (Handle and wheelie). Wide open on the limiter out of the hole. Nothing more rewarding than to beat a bigger bike. Setup is everything on these as most are modded and produce similar power.