I MYSELF AM PLANNING ON BUYING THE YOSHIMURA ... IT LOOKS GOOD AND I HAVE IT ON MY STREET BIKE AN LOVE IT .....IT COMES WITH STAINLESS HEADTUBES A REEL BONUS .....

 

I have a Yoshimura on my 400ex, and It sounds very nice.. I recomend going with the full system, not just the slip on. the slip on only gives more top end power, and not really any low end or mid. the full system increases mid-top, without hurtin your current low end. it is a little costly though

 

I have a MegaMax II and love it. I run it without the disks and got incredible gains. Especially the midrange to the top. I only have the slip-on, a K&N w/ outerwear and proper jetting and I can keep right along side my friend with a full yoshi even pull away from him in certain instances. I really don't see that yoshi's are as great as people are hyping them up to be. And I think my Megamax sounds meaner. I do hear alot of good things about Big Gun and you can get a full system from Rockymountain for almost half the cost of yoshi.
I don't mean to offend die hard Yoshi fans. Their systems are killer on street bikes, but you can get a better off-road one for less.

"If it's got wheels or a skirt, you can't afford it."

 

I ride with 10 guys that all have 400ex's. Everything from stock pipes to complete systems (i.e. Big Gun) Nobody's quad is noticably faster. I have the Big Gun, proper jetting, K&N, drilled out air box, etc. Don't let anybody fool you, all aftermarket pipes really do on a stock engine is make more noise, which makes a lot of people think they are going faster. Look at Big Gun's dyno specs for this bike and many other applications. A little more top end but actually less power everywhere else than stock. Aftermarket pipes are not worth the money. Honda does its homework and really knows how to make an exhaust system. If you are going to do extensive mods (more displacement, porting, cam, bigger carb, etc) than yes, you need to flow more exhaust, but on a basically stock engine it's pretty much not worth it. Big horsepower claims are just that - big advertising claims from the companies manufacturing them.

 

To me the pipe is worth it just so you can hear the motor talkin. I have an FMF powercore IV on mine with a stage two jet kit and K&N filter with skin and no airbox lid. It runs great and sounds good too.

 

The pipe is worth it if merely for the look on peoples faces when you fire that 400 up. I run FMF's Powercore IV with spark arrestor and it sounds and looks great.

00' 400EX, FMF powercore IV with spark arrestor, Dynojet stage 1, 14 tooth sprocket (on the way).

 

why do you have your air box li off with a 155 main?

 

The dyno charts I've looked at all show a moderate increase in HP for slip-on pipes(1-2hp through the entire RPM range). But if you think about it, it's only a 5-10% gain in top-end (27->29hp), but it's also a 10-20% gain in low-end/midrange (10hp->12hp), which is definietly noticeable. Also, what those HP graphs don't show you is torque, which is very important for woods riders like me. The torque increase from just a slip-on silencer is VERY noticeable! I can ride my brother's stock 400ex, and notice right away that it doesn't pull in the lower RPMs nearly as well as mine does (with a WB E-series). I think that $200 is a LOT of money to spend on a muffler (I can get a glasspack from the local auto store for 15 bucks, which is basically the same thing), but as far as quad modifications go, it's worth the money, compared to other mods.

 

my airbox lid is off because that's what is recommended by BIG GUN and 155 is the recomended main also