Exhaust valve

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Whip!

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Can anyone explain to me the theory/function of the exhaust valve. The servo controlled cable operated one at the bottom of the header. I guess the engine likes a little back pressure under certain conditions. What are the conditions that open and close it? Based on RPM I'm assuming. Or start up, I dunno. Is it incremental, or more like an on/off situation. Just curious. I installed an aftermarket exhaust on an R6 for a guy a little while ago that omitted this part. It seemed to start a little harder after that.... on an EFI bike.
 
the valve opens at a certain rpm. it gives you more torque at lower rpms, but allows you good top end once flow volume becomes more important at higher rpm.
 
Aaah. I guess that explains why the higher performance exhaust systems would omit that part. Because They would be spending more time at high RPM. I was mostly curious because I've never seen any maintenance procedures for it, and wondered what would be the symptoms of it wearing out or failing. Seems like a moving part like that in such a hot place would be prone to corrosion.
 
Here it is for anyone else that might be curious like I was. For some reason I was picturing in my head a butterfly valve, but it is actually more like a guillotine. On the bell crank where the cables attach there are some bunny horns (...devil ears? I'm goin' with bunny horns). They rest at the 9:00 position. Inside the guillotine is mostly closed with some open space at he top.
bellcrank9.jpeg
valve9.jpeg
Moving around as the bunny horns get to 12:00 the crank feels neutral and will balance there. At this point the guillotine is fully open and barely visible.
bellcrank12.jpeg
valve12.jpeg
Nudge it a little further and it will fall open and land at 2:00. Here the guillotine is beginning to close again on the other side.
bellcrank2.jpeg
valve2.jpeg
The actuator servo that makes all this happen is mounted to the frame up near the steering head.
actuator.jpeg
 
Whip! said:
Aaah. I guess that explains why the higher performance exhaust systems would omit that part. Because They would be spending more time at high RPM. I was mostly curious because I've never seen any maintenance procedures for it, and wondered what would be the symptoms of it wearing out or failing. Seems like a moving part like that in such a hot place would be prone to corrosion.
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You definitely should service it with some copper grease, regularly. Otherwise it has a habit of seizing up. Service procedure is documented here: http://www.cartestsoftware.com/fz1/exupmaintenance.html
 
Thats great, thanks. I'll definitely be doing that when this thing goes back together. One question though. What is this copper grease you speak of? The article mentions there could be several acceptable kinds but doesn't recommend one. I have some Permatex copper anti-seize that I like to use on exhaust bolts and slip joints. Will that work, or do I need to look for grease?
 
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