I never tried any of the aftermarket pipes, but several posts I've read implied that all you get is noise, but nothing significant in the way of power increases. (I think even the stock pipe is a little bit loud, but others don't seem to find it offensive, so I guess I'll leave it alone).
Possibly they might move the owere around from top to bottom or vice versa, but no real overall gains that I've heard of.
And yes, I'm riding a 400exc these days. My grandson calls it "Poppy's Punkin Bike". Finally graduated from the XR 250.
The T-4 definatley makes a difference in the power. It gave my 400 more hit on the bottom and stronger pull through the midrange. I liked it. I felt the 400 was slow to get the front end light stock and the exhaust helped that. I can't see how anyone could say they didn't notice a difference after trying both. :think Maybe if you were not able to use the power the 400 has as is. You might not notice the increase.:p I think guy's are going to have to come to the realization these current 4strokes are not going to be quiet. The T-4 is loud! If you are not going to piss off the neighbors I would highly recommend it.
it DOES irritate the neighbors. you are kidding yourself if you think it doesn't matter, even if you think you are ok b/c all you ride is closed course. i wish all the bikes were as quiet as stock ktm's, we'd have lots more places to ride.
Sad but True, Lawman. We either have a quiet future or we will have no future at all.
You're right, Wild Hare, I don't wanna hear a 426F, at least not one with a Big Gun or Yosh on it, although I'm not overly bothered by the stocker. Yeah, it's louder than it should be, but it's not insane. Sometimes I ride a 520 (EXC), and it's a little louder than my 400EXC, but it's only bothersome when you really hammer the throttle.
At some point we're all gonna have to give up the extra 1.5 hp and ride quiet, or go get a bigger motor and leave it stock.
I put a stock SX silencer on my '00 400 exc. It woke up the power band and makes it funner on a track or in sand or washes. On tight trails I like the quiet torque the EXC silencer provides. Less noise will equal more trails in the future for sure.