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Discussion Starter · #1 ·
Ok so I'm looking for a definitive answer on this one. I have heard different opinions but I would like to know the fact about the exhaust valve and what is it's purpose.

Is it strictly for noise control or does it affect power too?
 

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It does, it increases backpressure at lower rpms to help the bike be more responsive. Also it helps with emmision controls. It was first introduced in the late 80's/early 90's with the FZR1000? EXUP
 

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Discussion Starter · #5 ·
It does, it increases backpressure at lower rpms to help the bike be more responsive. Also it helps with emmision controls. It was first introduced in the late 80's/early 90's with the FZR1000? EXUP
So it's pretty safe to say that ANY slip on, even if it keeps the boom box, needs a tune. Where I'm going with this is that some manufacturers claim that if their pipe works with the boom box, no tuning or remapping is necessary and you will still show gains. I'm a little skeptical on that claim, that's why I'm trying to find out for sure.
 

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You've already answered your own question.
 

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So it's pretty safe to say that ANY slip on, even if it keeps the boom box, needs a tune. Where I'm going with this is that some manufacturers claim that if their pipe works with the boom box, no tuning or remapping is necessary and you will still show gains. I'm a little skeptical on that claim, that's why I'm trying to find out for sure.
There are no free lunches and few, if any, honest claims from manufacturers. Wait until you can get the exhaust you like, a PCIII, and a dyno tune. Then, you will be very happy with the end results.
 

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Discussion Starter · #8 · (Edited)
You've already answered your own question.
See I'm not sure what to believe. I just installed the MPG Growler which hooks up to the boom box and took it out for a spin. It feels like the bike has more kick, especially off the line in the low RPMs... which doesn't make sense since the valve is supposed to make it more responsive in that RPM range... Go figure
 

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Contrary to what some say, no engine wants "back pressure". What an engine wants, and in many cases what these people really mean, is the "ram tuning" or "pulse tuning" that is associated with relatively small diameter header pipes of the correct and relatively long length, which inherently result in back pressure. The back pressure, BY ITSELF, is a BAD thing, by reducing scavenging during the valve overlap period. But when correctly tuned it results in a strong negative-pressure pulse during valve overlap. A butterfly restrictor is just going to cause positive back pressure, without the side benefot of the following negative-pressure pulse.

The butterfly gizmo in the exhaust is a noise and emissions thing, although in some cases (some years of ZX6R) it's been used to deliberately de-tune the top-end power of the engine. (Why they would do this, is not known.) In normal cases, the butterfly valve is wide open at wide-open throttle, therefore it has no effect. It partially closes at part throttle (when power output doesn't matter anyway). Doing this reduces the amount of pressure pulses sent down the pipe to the muffler (reduces noise) and by increasing the back pressure a little bit, it CAN be used to keep a bit of exhaust in the cylinder at part load ... acts kinda like an EGR (exhaust gas recirc) system with minimal extra complexity. Only reason to want to do that, is emissions. I suppose it could be used to soften the power delivery a little bit, although the secondary intake throttles are mostly responsible for that.
 
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Discussion Starter · #10 ·
Contrary to what some say, no engine wants "back pressure". What an engine wants, and in many cases what these people really mean, is the "ram tuning" or "pulse tuning" that is associated with relatively small diameter header pipes of the correct and relatively long length, which inherently result in back pressure. The back pressure, BY ITSELF, is a BAD thing, by reducing scavenging during the valve overlap period. But when correctly tuned it results in a strong negative-pressure pulse during valve overlap. A butterfly restrictor is just going to cause positive back pressure, without the side benefot of the following negative-pressure pulse.

The butterfly gizmo in the exhaust is a noise and emissions thing, although in some cases (some years of ZX6R) it's been used to deliberately de-tune the top-end power of the engine. (Why they would do this, is not known.) In normal cases, the butterfly valve is wide open at wide-open throttle, therefore it has no effect. It partially closes at part throttle (when power output doesn't matter anyway). Doing this reduces the amount of pressure pulses sent down the pipe to the muffler (reduces noise) and by increasing the back pressure a little bit, it CAN be used to keep a bit of exhaust in the cylinder at part load ... acts kinda like an EGR (exhaust gas recirc) system with minimal extra complexity. Only reason to want to do that, is emissions. I suppose it could be used to soften the power delivery a little bit, although the secondary intake throttles are mostly responsible for that.
:+2: Thank you! That was the answer I was looking for.
 

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Contrary to what some say, no engine wants "back pressure". What an engine wants, and in many cases what these people really mean, is the "ram tuning" or "pulse tuning" that is associated with relatively small diameter header pipes of the correct and relatively long length, which inherently result in back pressure. The back pressure, BY ITSELF, is a BAD thing, by reducing scavenging during the valve overlap period. But when correctly tuned it results in a strong negative-pressure pulse during valve overlap. A butterfly restrictor is just going to cause positive back pressure, without the side benefot of the following negative-pressure pulse.

The butterfly gizmo in the exhaust is a noise and emissions thing, although in some cases (some years of ZX6R) it's been used to deliberately de-tune the top-end power of the engine. (Why they would do this, is not known.) In normal cases, the butterfly valve is wide open at wide-open throttle, therefore it has no effect. It partially closes at part throttle (when power output doesn't matter anyway). Doing this reduces the amount of pressure pulses sent down the pipe to the muffler (reduces noise) and by increasing the back pressure a little bit, it CAN be used to keep a bit of exhaust in the cylinder at part load ... acts kinda like an EGR (exhaust gas recirc) system with minimal extra complexity. Only reason to want to do that, is emissions. I suppose it could be used to soften the power delivery a little bit, although the secondary intake throttles are mostly responsible for that.

:+1: This is what is about really. I didn't mean much backpressure, but few and at lower rpms is ok.

Cesarb714 your bike will breath freely but it will not be 100% Me likey my toys to be spot-on, some people don't care that much.
 
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