I am sure this question has been asked a million times here, but I am a newbie to the site. I have a 02' 400ex and rejetted and added the K&N Filter. Now I am ready for a pipe. What do you all recommend. (I would like to be able to adjust the noise level to keep the tree huggers happy)

 

On a stock engine don't bother with a pipe. The 400ex doesn't see much gains with a pipe. Some magazine did a shootout a few months ago and the average gain was about .5 - 1.5 hp. The top performing pipe added a whopping 2 hp at a cost of about $500. Not worth the trouble in my opinon. In addition all aftermarket pipes will be quite louder.

 

I dont care what anyone says, when I put my pipe on I really noticed gains.Dont buy a header pipe, Honda did good making almost all the power it could out of the stock header.Plus, thats rear wheel hp on those dynos.I got an FMF, but all the pipes are about are about the same performance wise.FMF and Yoshimura make quiet versions of their pipes I think.

 

It's all in your mind. I sounds louder and deeper so you this it has tons of power. It doesn't, the dyno is not tricked by this.

 

Well, mr 250R, you're pretty much wrong. Don't believe everything you've read in a magazine. I put a pipe, k&n, and jet kit on my 400ex, and when I drag race a stock 400ex (which is a true test of the added power) I kill the stock bikes. In a straight line drag, I pull away from the stocker from 3rd gear to 5th. Going up hills in the dunes, I can pull hills in 3rd and 4th gear that I couldn't do in 2nd gear when my bike was stock. Another thing, the dyno tests in the magazine just report the peak horsepower gains. Where you really notice the gains are in the mid range to the top. I'd say that adding my pipe was worth while. That's my 2 cents worth, but after 20 years of riding experience what the heck do I know.

 

Chad,
I appreciate your insight, I'll go with the 20 years. I have been riding in the dunes and I would like more power. Should I upgrade the header as well or is a slip on enough? I have been looking and found that the header & pipe is about twice the price of the slip on. Is there twice as much performance with the header or is the stocker good enough?

 

If your talking peak HP you're correct in the 1.5hp gains. In the low and midrange there is up to 5HP. I put a White Bros on the 400ex rejetted and it made a signifacant differance in the power. Look at the curve of the Dyno chart will tell you more. The White bros slip on for $225 is one way. Keep the stock head pipe unless you plan on big bore in the future. Dirt Wheels did a shoot out and posted all of the dyno charts. Some made less Top End HP, but some picked up almost 6 HP in low and midrange power.

It couldn't have been all in my mind, my mind is shot.

Smitty

 

Chad, I've been riding since 1980, have owned and built over 20 high performance atvs in that time. You proved my point when you said "I put a pipe, k&n, and jet kit on my 400ex..." We are taking about the pipe. A pipe on it's own yeilds minimal gains on a 400ex. Now you mention the K&N. A high flow filter and improved air flow (as in holes in airbox) will produce more HP than a pipe on a stock 400ex.

As for the increase in the low-midrange, yes you will get up to a 4 hp increase in that range with the right pipe but most 400ex riders would agree that the machine has strong low-mid end already. What is lacking is the top-end punch. Looking at dyno tests on a stock bike (400ex)will reveal that the pipes that give you a strong low end increase will sacrifice the engines topend performance. The reason for the lack of power increase on the 400ex's top end is the fact that the exhaust valves on a stock engine are almost perfectly matched to the stock pipes exhaust output flow.

Please see
attached link

When visiting this link keep in mind full-race is a highly modified engine.

 

I didn't expect to spark so much controversy, I love it! After all of your input I am going to go ahead and pick up a slip on tonight. It seems everyone agrees on a White Brother's pipe. I will be sure to keep you all posted as to how it works out.
Thank you for all of your input. If there is anything else that you all may recommend I do please let me know. I have some room left on my credit card. SPEED is the goal here.


Keep the rubber side down!