I was humbled today when I raced my hopped-up 400 ex (White Bro's E pipe & K/N air filter) against a stock 400ex. I weigh about 60 lbs more than my buddy- We both were powershifting ( I know, it's not good)-...

the results...

It was a tie.... We ran the race a few times- and I didn't see much improvement. Do you guys think the 60 lbs makes THAT MUCH difference?
Is it possible that my Slip-On WHite bro's is causing an air/fuel mixture imbalance? I know sometimes pipes can throw this a little off...

Thanks for your thoughts....

 

Exchange ATVs and see who wins.

Diogenes

 

Oh, yeah: Why not read your plug to see if you're jetted correctly?

Diogenes

 

We did exchange bikes... and he would win (on the hopped up) only by a few feet. ...which makes me think the 60 lbs difference isn't that big of a deal.

 

You should definitely notice a gain in power with a pipe. A piped bike should take the stocker off the line and never look back. When my 400 was still stock and I raced my friend with a T4, I beat him, but that was because I had better tires and hooked up. Under better traction, he won many times. Since you tried switching bikes, I would say you should take a look at your plug. It is probably snow white(lean). Use one of the posts on jetting to help figure out how much bigger you need to go. You should need to jet up with any pipe, or even just a K&N.

 

With only the mods you have that is not really gonna make much differance on top end. Mayb .5-1 mph on top end.

 

Simply adding a pipe and an air filter (which adds no performance, I've timed stock vs K&N on 2 different 400s) will not account for 60 lbs of body weight.

Despite what many will tell you, a slip on silencer, or even a full exhaust will not make more than a small difference in the mid range on a 400EX..

Personally I have smoked lots of piped bikes with my 400 when it was stock at the races.

If you want real power, you'll need to open up the engine and make a series of changes. This really isn't very costly if you can do most of the labor yourself (I have about $800 in my setup, and it will seriously leave a stock 400, and will pull away from Raptors as well).

Things to get:

JE Piston - if you don't want to sleeve get an 87mm, this will raise your displacement to 416 and your compression to 10.8:1. If you don't mind running race gas, go with higher compression. Cost $120 + top end gaskets $25, plus cylinder boring, no more than $35.

XR400 or GT Thunder cam. Depending on how much bottom end you need, if you want more top, go with the GT Thunder. Cost $115 - $165 depending on what you choose.

Mild head porting and port matching - cost - approx $50

FCR 39mm carb - cost approx $450

Do this, and you'll break a lot of Raptor owner's hearts....

Total cost < $900....

 

What size main jet do you have in it? When i put my DMC full exhaust and K@n filter on mine, i raced my friend's stock 400EX, and i barely beat him. I read my plug after that and i was rich, so i ended going down two sizes on my main jet. After i rejetted, i would walk away from him. Jetting makes all the differance in the world when your only talking about a couple of horsepower. If you run it rich, you are canceling out the gains that you should get from the pipe. Get rid of your airbox lid, put in a 155 or 160 main jet, and you should be able to walk away from a stock 400EX.

 

see these are 440's i got a 465kit with a lightned flywheel, 6 degree advanced timing, titanium valves ,Custom race cam, 3-way valve job, port polished, hot rod (rod),customed made cam chain, Lrd big bore exhaust, trued and welded ,had the crank shaved down , alcohol for my 39 fcr carb ,i got an 8 inch swing arm, chromed frame, polished head,case custom design paint on plastic


((((((AS THE T-REX EATS THE RAPTOR))))))

 

From the New 4 wheel ATv Action Mag

Stock 400EX 26.9HP Max
With FMF pipe 27.8HP Max
With K&N jet Kit and Airbox lid off 28.6HP Max

Doesnt ssem like the pipe is worth the $$$ It does have a much better curve with more usable power but at $500 for under 1 HP!!!!



Mac