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Message started by Robertomoe on 08/18/08 at 17:59:01

Title: exhaust butterfly valve
Post by Robertomoe on 08/18/08 at 17:59:01

I was reading up on intruder 800's (I can dream, cant I?) and this guy's website was talking about the same thing.. (Toymaker, was it?) was talking about- that running more open pipes compromise backpressure and can actually cause you to lose power. This guy said basically the same thing- drag pipes are designed to give you power at the high end of the RPM band, like you would want and use at a drag strip at the sacrifice of low and mid range power. To address this problem if you like the sound of your pipes, he showed a diagram for a valve made from a washer and some bolts. He claims this allows you to adjust the pressure and have the ability to open up the pipe if you want to let out the top end.

Has anyone done something like this or can relay an experience? If it's supposed to work, I might go ahead and try it and get on a dyno and see what I get.

Title: Re: exhaust butterfly valve
Post by rigidchop on 08/18/08 at 18:02:58

they make a similar pipe for hd. i believe its called peacemaker, you can open it up for highway use and quiet it down for in town use. what you read is true though, drag pipes are made for what they say, drags, which is wide open. generally you lose a bunch of low end torque with this type of pipe, but gain hp in the top end.

Title: Re: exhaust butterfly valve
Post by Charon on 08/18/08 at 18:22:16

There are at least a couple of bikes that already use such a system, controlled by the engine management computer. One is called EXUP, but I don't remember what the acronym stands for. I am not sure whether it simply adds back pressure, or whether it changes the exhaust system in some other way.

My SeaDoo boat has a Rotax two-stroke engine which uses guillotine valves on the exhaust ports, controlled by the computer. At low power the valves are closed, and lower the top of the exhaust port. At high power the valves open up and allow the exhaust ports to open sooner. The system is said to spread torque a bit. As I read it, they are not supposed to increase back pressure, but to change exhaust port timing.

I was watching a go-kart race some years ago in which two-stroke engines were being used. Many (probably all) of the racers had an expansion chamber arrangement resembling a trombone slide, which allowed the drivers to move the expansion chamber while driving. As the revs come up, the expansion chamber needs to move closer to the exhaust port.

Title: Re: exhaust butterfly valve
Post by Crotchrocket on 08/18/08 at 19:06:31

EXUP Exhaust ultimate power valve.

Yamaha's trademark name for an exhaust valve.