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Discussion Starter · #1 ·
If you replace the OEM muffler on the 2007-2008 ZX-6R with an aftermarket slip-on muffler, removing the butterfly exhuast valve and cables, but leaving the servo in place and ACTIVE (i.e. still electrically activated by the ECU), are there any negative effects?

I'm asking because I found a Chinese copy of the Yoshimura RS-5 at a price I can handle. The genuine Yoshimura RS-5 installation instructions say to leave the servo undisturbed. I am assuming that this is to prevent the ECU from issuing a trouble code. That's fine.

But, Kawasaki must have that butterfly exhaust valve in there for a reason other than to partially close it above 12,000 rpm to keep the maximum exhaust db below 2007 California or EPA limits. (They could easily have met the noise limit by simply making the muffler itself more restrictive). So, I am wondering if they put the valve in there to use it at low to moderate rpm ranges to deliberately add some back pressure to counter the very long (288 degrees!!) intake valve timing needed for 16,500 rpm, which would otherwise result in incoming mixture simply blowing right out the exhaust valve at low rpm.

Anyone out there have actual experience with removing, or simply holding the butterfly valve open ALL the time, and experiencing the resulting engine performance?

Jim G
 

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If you replace the OEM muffler on the 2007-2008 ZX-6R with an aftermarket slip-on muffler, removing the butterfly exhuast valve and cables, but leaving the servo in place and ACTIVE (i.e. still electrically activated by the ECU), are there any negative effects?

I'm asking because I found a Chinese copy of the Yoshimura RS-5 at a price I can handle. The genuine Yoshimura RS-5 installation instructions say to leave the servo undisturbed. I am assuming that this is to prevent the ECU from issuing a trouble code. That's fine.

But, Kawasaki must have that butterfly exhaust valve in there for a reason other than to partially close it above 12,000 rpm to keep the maximum exhaust db below 2007 California or EPA limits. (They could easily have met the noise limit by simply making the muffler itself more restrictive). So, I am wondering if they put the valve in there to use it at low to moderate rpm ranges to deliberately add some back pressure to counter the very long (288 degrees!!) intake valve timing needed for 16,500 rpm, which would otherwise result in incoming mixture simply blowing right out the exhaust valve at low rpm.

Anyone out there have actual experience with removing, or simply holding the butterfly valve open ALL the time, and experiencing the resulting engine performance?

Jim G
Working on that same thing man I took out butterfly and servo out in the code eliminator gonna just put on a shiny mid and a tip with removable DB killer hope that is not gonna be to bad on it
 

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Working on that same thing man I took out butterfly and servo out in the code eliminator gonna just put on a shiny mid and a tip with removable DB killer hope that is not gonna be to bad on it
Let me know how it works out the people here are awesome lots of knowledge I hope to learn AMAP
 

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Pursebully
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There's a ton of info on the forum if you search for it. The servo and servo eliminator have been the topic of many threads.
 
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Discussion Starter · #5 ·
I will try to search the forum more carefully. The Chinese kit has some shortcomings versus the Yoshimura, but costs a lot less. Key points:

- It does not include robust mounting tabs liek the Yoshimura. It uses what appears to be a carbon fibre strap that gets secured to the same bolts as the OEM and Yoshimura mufflers do, and apparently goes into the same midpipe clamp as the OEM and Yoshimura do

- It does NOT provide the heat reflective self-adhesive material that the Yoshimura kit provides to help insulate the motorcycle tail area from the exhaust heat. You can use the OEM material, or better, buy a piece of heat reflective self-adhesive material and cut it to fit (The Yoshimura kit includes a helpful template to do that, which of course the Chinese kit lacks)

- The genuine Yoshimura RS-5 accepts a (provided) db killer, and is actually only 4db louder than OEM even without a db killer insert installed. With the db killer installed, the Yoshimura RS-5 is actually slightly quieter than the OEM muffler. The Chinese version does not provide an installable db killer, and its noise level is not quantified, although the vendor tells me"the voice sound nice" :)

- I asked what it weighs, and the vendor replied that it is about 2200 grams = 4.85 lb. The OEM muffler with butterfly valve weighs 9.3 lb, so you get a weight reduction of 4.45 lb. This is a BIG deal, and my reason for trying to do this mod. That 4.45 lb, placed SO high on the bike, and SO far rearward, contributes to a top-heavy feel when maneouvering the bike in a parking lot, or pushing it around in a driveway or garage. The lighter weight also means far less static and dynamic load on the muffler mounting system, which is what enables the CF strap mount

- The Chinese version comes in 2 versions, both of which have a CF tip. The body wrap is either s.s. or CF and you need to specify which version you want when you order. The CF version has the advantage of barely getting warm, let alone hot (based on 4 previous CF mufflers I have had on other bikes), so you limit the heat transfer to the tail AND you can cover the bike right after a ride without waiting for the exhaust to cool. The difference in weight between the 2 versions would be miniscule, since the difference is ONLY the wrap. Interestingly, the porduct photos show a "grayout" box over what looks VERY much like the Yoshimura logo on the CF version of the muffler. The s.s. version has no product logo on it, but the vendor provides what look like stickers. :)

- The Chinese product does include an offset pipe to connect the muffler to the OEM mid-pipe

- I anticipate that there might be some mounting issues since the Chinese version mounts differently than the OEM and Yoshimura systems do, as "things happen", but the over 40% lower price outweighs the possibility of some mounting issues.

My biggest concern is simply how the change might affect engine performance. The Yoshimura RS-5 claims a 1 rwhp gain, but the Chinese versions is a complete unknown, and of course the Yoshimura 1 rwhp gainclaim might indeed be accurate - at one certain rpm point, but what about within the entire rpm range, especially the low and moderate rpm ranges. It would be an "experiment" that the big weight saving makes worthwhile to do unless someone points out some signfiicant negatives to losing the butterfly valve.

Jim G
 

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Pursebully
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As you've found out, slip on mufflers don't give you much (if any) HP gain. They are purely for weight savings and sound.

There are no real negatives to removing the butterfly valve. Some have stated that there is a very slight change in bottom end torque, but these bikes don't spend much time operating in the bottom end.
 
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Discussion Starter · #7 ·
Well, I have read the entire listing of ALL forum postings related to the exhaust valve, and have no better clarity than I did before reading them!

It seems thta everyone has an opinion, but no one has the actual testing data to answer the question: If you remove the exhaust butterfly valve by changing to an aftermarket slip-on muffler, do you affect the performance of the engine negatively in any way?

Some people think you will lose low and mid range torque. Others say you won't (That the exhaust valve is a noise control device only). Some say that you will lose torque but can regain it by using a Power Commander (or ECU flash I presume).

I just want to lose the 4.5 lb of weight that you lose on the bike by changing from the 9.3 lb OEM muffler with valve to a 4.85 lb aftermarket slip-on without the valve. But, I don't want to do it if I will lose low to mid range torque. Yes, I know to disconnect the valve cables BUT leave the servo operating to avoid a trouble code. But, what engine performance change(s) might I experienced? (Some posters said you lose low rpm torque but others say there is no discernible difference)

It's hard to believe that after a decade and a half since these bikes were manufactured, no one seems to REALLY KNOW. :(

Jim G
 

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Discussion Starter · #8 ·
Idea for an experiment:

- Disconnect the servo ELECTRICALLY from the bike's wiring harness, replacing it with a servo eliminator. That should leave the exhaust butterfly valve in the default OPEN position, which would simulate taking the valve out of the exhaust

- See if the engine's performance is affected at ANY rpm range: low, middle, or high by this

- See also if the engine exhaust SOUND is affected at ANY rpm range: low, middle, or high

IF performance is affected, then we know that the exhaust butterfly valve has PERFORMANCE effects.

IF exhaust sound level is affected, then we know that the exhaust butterfly valve has exahust sound level effects.

Any flaws in my reasoning?

Hasn't anyone actually done this in a decade and half since the 2007-2008 ZX-6R was released?

Jim G
 

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I haven't read the entire thread word for word, sorry if I'm regurgitating info.

The exhaust servo does NOT improve performance in any way. It reduces sound at high RPM's. If you ever get a chance to watch one on the dyno it will rev up and start to pull hard about 3/4 of the way through the power band. Right when it starts to wind out you can see the cables move. It has a similar effect as chopping the throttle from 100% to 90% even though on the dyno you can clearly see the throttle is wide open.

It's for noise only. Manufacturers are making different excuses while trying to not pi$$ off their customers. Restricting your exhaust does not help performance ever. Yes we can get in to resonant frequencies but that's more of a header length/expansion chamber situation. Still nothing to do with restriction.

Brocks performance did a nice write up. He touches on it in quite a few recent videos on his youtube channel (most recent being the ZH2). Lots of info on modern bikes regarding the exhaust servo. He calls it by it's Yamaha nomer which I can't remember at the moment. Still the same junk, still the same conclusion nearly 20 years after it's invention.

My conclusion: Exhaust servo and butterfly valve are best used as a paperweight or scrap metal bin fodder.
 

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Discussion Starter · #10 ·
Thank-you, Brad! For those who don't know, Kawasaki Brad worked in the Kawasaki world for over 2 decades in a variety of technical and MC show roles. He knows his stuff.

Jim G
 

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Discussion Starter · #11 ·
I just ordered a Servo Eliminator from Brad. Once it arrives, I plan to first test in-person myself how much effect the servo has by simply electrically disconnecting the servo from the bike's wiring harness, leaving the servo, the cables, and the valve physically in place but inactive.

I will try to detect any performance, sound, or other differences, if they exist. Based on Brad's comments, I do not expect to see, hear, or feel any differences between servo being active and servo being inactive.

I have ordered the Chinese clone of the Yoshimura slip-on exhaust. Once it arrives (weeks away), I will swap it in to replace the OEM muffler and valve, and also at that time physically remove the servo. If this all works, the total weight saving should be approximately 5 lb. I have 7 more lb of other weight reductions already done or awaiting ordered parts. So, I will hopefully remove over 12 lb of weight, most of it from the top of the bike, or outboard on the sides. This will make a noticeable difference in handling while riding and also while manhandling the bike around parking lots, my driveway, or my garage.

Jim G
 

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Discussion Starter · #12 ·
I've ordered the Chinese clone of the Yoshimura RS-5. Here is a photo showing the 2 versions available (stainless steel or carbon fiber - I ordered the carbon fiber), plus the installation parts that come with it:

Dvi cable Ac adapter Adapter Automotive lighting Gadget


The ad warns you that no instructions come with it (unlike the more deluxe Yoshimura and Akrapovic kits). :)

The "strap" obviously surrounds and supports the muffler, and secures to the existing mounts on the tail that the top of the OEM muffler attaches onto.

The 2 springs secure the offset pipe to the muffler.

But what do the 2 long and narrow metal pieces, each with 2 holes in it, do?

Perhaps someone familiar with the 2007 -2008 tail section and muffler can clue me in?

Jim G
 
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