Butterfly exahust????? - ZX6R Forum
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post #1 of 17 Old 03-21-2019, 08:19 AM Thread Starter
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Butterfly exahust?????

Please does anybody know how the butterfly on the exhaust can affect the performance of my bike?
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post #2 of 17 Old 03-21-2019, 09:17 AM
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The butterfly valve is used to vary back pressure in the exhaust to help fill in holes in the torque curve at lower RPM and sometimes to help get the bike past noise regulations.


Mark

1998 ZX6R
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1982 GS1100E
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post #3 of 17 Old 03-21-2019, 09:29 AM
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..... in a perfect world, the butterfly would be there as a performance aide. It is in fact a gizmo to defeat the DOT/EPA noise measurement test.

The valve moves to reduce the exhaust pipe area, thus changing back pressure and muffling some of the noise from the engine. It is only rotated into position at 50% max RPM, over a narrow band of RPM. Above and below that narrow span of RPM, the butterfly is wide open. No effect, at any other RPM.

You can simply disconnect the cables from the servo, that move the valve if you want to check that out. The valve is spring loaded to stay wide open.

If you leave the electrical wires connected to the servo, the ECU doesn't know anything's changed. No codes, lights, or changes in performance.

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post #4 of 17 Old 03-21-2019, 03:19 PM
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Originally Posted by RJ2112 View Post

If you leave the electrical wires connected to the servo, the ECU doesn't know anything's changed. No codes, lights, or changes in performance.
This part varies between model years.
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post #5 of 17 Old 03-21-2019, 06:27 PM
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It is only rotated into position at 50% max RPM, over a narrow band of RPM. Above and below that narrow span of RPM, the butterfly is wide open.
Well, how about that? The one on my GSXR1000 moved throughout the lower revs to keep the torque curve dead flat and smooth as well as being used to help with the noise limits. Doesn't seem like there is any reason to keep the valve on a ZX6R then.


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1982 GS1100E
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post #6 of 17 Old 03-22-2019, 03:08 AM
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Well, how about that? The one on my GSXR1000 moved throughout the lower revs to keep the torque curve dead flat and smooth as well as being used to help with the noise limits. Doesn't seem like there is any reason to keep the valve on a ZX6R then.


Mark
Put the bike in neutral, touch one of the cables controlling the butterfly valve, and slowly increase RPM. The cable won't move til RPM hits about 6K, then lets go again about a K later.

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post #7 of 17 Old 04-03-2019, 11:47 AM
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This is Intriguing - I've been wanting to learn about this. Cuz you see, my previous bike (2005 CBR F4i), didn't have all these gizmos. I did buy it with a 2 Bros exhaust, which sounded deep and awesome (compared to the stock exhaust on ZX6r). I've been wanting to change the exhaust, but DON'T wanna damage the engine or lose power, or make any negative mods to the bike. I'd like to learn more about this...

Thanks!

Current Bike: 2016 ZX6R KRT (ABS) (getting to know)
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post #8 of 17 Old 04-03-2019, 09:53 PM
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This is Intriguing - I've been wanting to learn about this. Cuz you see, my previous bike (2005 CBR F4i), didn't have all these gizmos. I did buy it with a 2 Bros exhaust, which sounded deep and awesome (compared to the stock exhaust on ZX6r). I've been wanting to change the exhaust, but DON'T wanna damage the engine or lose power, or make any negative mods to the bike. I'd like to learn more about this...

Thanks!
So long as the catalytic converter remains in place in the header, sufficient back pressure will remain to protect the engine. You can do nearly anything you want after that point with minimum repercussions to the engine.

The reality of it is that the greatest advantage of aftermarket slip on mufflers is weight reduction, and more noise.

If you want more power, increasing fuel to enrich the charge is the next most common move. PC5, etc. Possibly reflash the ECU instead......

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post #9 of 17 Old 04-04-2019, 03:24 PM
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Originally Posted by RJ2112 View Post
Put the bike in neutral, touch one of the cables controlling the butterfly valve, and slowly increase RPM. The cable won't move til RPM hits about 6K, then lets go again about a K later.
...yeah ummm my '17 opens after 3500-4000rpm and/or when you command more than 20-25% TPS. Maybe this is a KRT Edition feature.
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post #10 of 17 Old 04-04-2019, 04:28 PM
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...yeah ummm my '17 opens after 3500-4000rpm and/or when you command more than 20-25% TPS. Maybe this is a KRT Edition feature.
Opens, or closes?

No cables attached, the spring loaded valve is held full open..... At least on my '09....no tension on the cables until as I described. Ymmv

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post #11 of 17 Old 04-05-2019, 01:01 AM
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Quote:
Originally Posted by RJ2112 View Post
..... in a perfect world, the butterfly would be there as a performance aide. It is in fact a gizmo to defeat the DOT/EPA noise measurement test.

The valve moves to reduce the exhaust pipe area, thus changing back pressure and muffling some of the noise from the engine. It is only rotated into position at 50% max RPM, over a narrow band of RPM. Above and below that narrow span of RPM, the butterfly is wide open. No effect, at any other RPM.

You can simply disconnect the cables from the servo, that move the valve if you want to check that out. The valve is spring loaded to stay wide open.

If you leave the electrical wires connected to the servo, the ECU doesn't know anything's changed. No codes, lights, or changes in performance.
So you can make the stock exhaust louder for free? Not sure if i'm understanding.
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post #12 of 17 Old 04-05-2019, 05:00 PM
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@RJ2112 Yes opens. The valve on my bike (2013-18) has 2 cables, one for each direction. No spring. Bike off = closed (my guess is to prevent debris from entering). The servo on mine also self tests at Key On Engine Off and after riding in the winter stripped the plastic gears inside after the valve seized shut (check my thread). Don't forget, they brought back the 636 in 2013, and Euro laws required emissions changes, so your 09 may be different.
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post #13 of 17 Old 04-05-2019, 05:12 PM
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So you can make the stock exhaust louder for free? Not sure if i'm understanding.
No louder overall, just slightly quieter, at mid RPM where they make the measurements.

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post #14 of 17 Old 04-07-2019, 03:34 PM
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So you can make the stock exhaust louder for free? Not sure if i'm understanding.
Interesting and a bit confusing topic, isn't it?!!

Quote:
Originally Posted by RJ2112 View Post
So long as the catalytic converter remains in place in the header, sufficient back pressure will remain to protect the engine. You can do nearly anything you want after that point with minimum repercussions to the engine.

The reality of it is that the greatest advantage of aftermarket slip on mufflers is weight reduction, and more noise.

If you want more power, increasing fuel to enrich the charge is the next most common move. PC5, etc. Possibly reflash the ECU instead......
Ah Ha... What Minimum repercussions are you talking about? I think it's important to know before one dives into it. In an ideal world, I'd like to remove the boxed exhaust "thingy" (before) the exhaust muffler; remove all the servo cables and servo unit under the seat, and then also replace the muffler with a 2 Bors / M4 type muffler. So basically, keep the stock headers, and line it up with aftermarket muffler (a simple design), without any negative effects to the bike.

More power, increasing fuel......NO thank you. I'd like to keep the fuel savings; power is plenty if we can ride the bike to its Max capability (which most people can't).

Current Bike: 2016 ZX6R KRT (ABS) (getting to know)
Ex Bike: 2005 CBR F4i (was smooth like butter)
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post #15 of 17 Old 04-07-2019, 05:43 PM
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Interesting and a bit confusing topic, isn't it?!!



Ah Ha... What Minimum repercussions are you talking about? I think it's important to know before one dives into it. In an ideal world, I'd like to remove the boxed exhaust "thingy" (before) the exhaust muffler; remove all the servo cables and servo unit under the seat, and then also replace the muffler with a 2 Bors / M4 type muffler. So basically, keep the stock headers, and line it up with aftermarket muffler (a simple design), without any negative effects to the bike.

More power, increasing fuel......NO thank you. I'd like to keep the fuel savings; power is plenty if we can ride the bike to its Max capability (which most people can't).
EPA mandates that the engine produces minimum emissions... The cat breaks down/burns off much of the unburnt fuel in the exhaust; for lowest emissions, the more lean the charge is, the less the cat has to do.

Lean charges are hotter than rich ones, as the excess fuel evaporates and cools the gasses. This reduces stress on the exhaust valves, and the valve seats. It also produces more power.

Many people go the route you describe, drop the prechamber, replace OEM muffler with a straight through glass pack. That can be done without additional fuel, it will be much louder, and won't make any more power than it did before. Might rev a bit more freely.

My '09 was equipped with an M4 GP bolted straight to the header when I bought it. I commuted with it that way for months, ~70 miles round trip each day. No fuel enhancer.

Now that I have had the OEM complete exhaust back on the bike for a number of years, I can comfortably state I get better MPG, with the OEM.

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