Cutting muffler length.. does it hurt the engine? : Honda CBR 600RR Sportbike Forum : 600RR.Net

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Old 10-31-2012, 10:23 PM   #1
DesertSoldier
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Cutting muffler length.. does it hurt the engine?

So I've seen a lot of guys on here cutting down the length of their muffler, and got to wondering whether or not it will hurt engine performance or reliability in the long run. The short answer to this problem is yes and no.

First off… How an exhaust works.

In my opinion, this topic is one of the most misunderstood around all of the engine performance mods between motorcycle enthusiasts and car enthusiasts alike. I have heard time and time again that an engine with a larger exhaust allowing more exhaust gases to flow from the engine will aid in performance. This is not necessarily true. Individuals tend to not know the difference between back pressure and velocity and how they coincide with one another in terms of exhaust gases. For an engine to run efficiently and produce maximum power gains, it must maintain a steady back pressure while also maintaining a constant optimal velocity for the engine. This means that if too much back pressure occurs by a highly restrictive pipe (worse case scenario) the exhaust gases can actually reverse flow sending them back into the chamber, and creating too high of a velocity which could damage the engine. Not enough back pressure and the velocity of the exiting exhaust gases will not have a high enough velocity causing a drop in performance i.e. HP. The back pressure and velocity, when balanced between each other at optimal levels, will aid in creating what is known as your power band. If you want a power band located at the mid-range of your RPMs then that is where you want little to no back pressure and maximum velocity of exiting exhaust gases.

Chopping your muffler comes in to play.

After that long course on back pressure and velocity of gases, I’ll now explain your muffler. Most you already know what a mufflers purpose in life is, and that is to adjust tone, volume, pitch, and dB of the existing exhaust gases. It’s nothing more than a fancy trumpet or clarinet… which ever you prefer. At the same time though the muffler will create back pressure and restrict velocity.

The problem I see with cutting the length of the muffler is it can actually disrupt the flow of exhaust gases, which will, in turn, lower the velocity altering your power band. It can also lower the amount of back pressure being produced. Now I cannot tell you how much altering this will causes because I have yet to get a second pipe I can cut on and run tests with. What I can say is with this drop in back pressure and velocity you will probably see more engine gunk build up internally, more heat being produced by the exhaust, and over all a less reliable engine when it comes to longevity of the motorcycle.

Like I've stated previously, I have yet to test this, but I do for see it being a problem in the long run. I’m not saying, at this time, that it is a bad idea, because the performance loss might be minimal, and lets face it, most of us never see this true end of our bikes. It typically gets wrecked or sold before it goes to the grave yard on its own terms. My professional opinion, at the time prior to testing, is it to do it because I don’t see cutting two inches off the muffler creating too much turbulence in the flow, but if you try to get exotic and cut more I would second guess whether or not it is worth it.

This book I just wrote will be available in hard and soft copy. lol
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Old 10-31-2012, 10:45 PM   #2
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Thanks for this. Actually thinking of gettin a shortened pipe.
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Old 10-31-2012, 11:06 PM   #3
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Shortly after posting this, a buddy of mine informs me he is willing to donate his yoshi to science. I have to same pipe so his will be cut 2". both pipes will be ran on the same bike (my bike), both pipes will have new packing inserted, and both pipes will be giving a 500 mile break in (before it gets to cold outside) with the same rider (myself) to insure accuracy in the testing. Fuel to air will be controlled by the same PC map for both pipes as well.

Test that will be done...

1. dB test
2. dyno
3. gas velocity test (through all RPMs)
4. pressure test (through all RPMs)
5. heat test (Headers, Mid-Pipe, Muffler)
The final test that will be ran, of coarse, is the best... coolness test. which one has more bling.

any more tests that you guys see fit to run, let me know. I have access to all kinds of cool toys so I probably have it.
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- Her name is PITA (Pain In The Ace)
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Galfer steel braided Brake Lines (Front and Back)
PSR click n' Roll shorties (brake and Clutch)
Shogun swing arm spools
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Old 10-31-2012, 11:31 PM   #4
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well here's my input. On my 2006 600rr I had the Arrow pipe that looked like a limp penis and I hated the way it stuck out under the tail. So I got it shortened by 2 inches. Took it to the dyno to see if it impacted any power and I lost 3hp. The week before I just got it custom mapped. Weather conditions and humidity were the same, not to mention it was done by the same dyno tuner on the same dyno. Just food for thought.
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Old 10-31-2012, 11:37 PM   #5
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Moved to a more appropriate section.
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Old 10-31-2012, 11:53 PM   #6
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Quote:
Originally Posted by sincalirider View Post
Moved to a more appropriate section.
Thanks for the move
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-street bike
02 GSXR 1000(Red/Black/Silver)

-Corner tuckin, go fast humming bird
- Her name is PITA (Pain In The Ace)
07 CBR 600rr (Blue/Silver)
Galfer steel braided Brake Lines (Front and Back)
PSR click n' Roll shorties (brake and Clutch)
Shogun swing arm spools
Shogun no-cut frame sliders
Vortex Steel sprockets (-1,+2)
RK Gold chain
Yoshi Full RS-5 Stainless/Titanium/CarbonFiber

more to come!
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Old 10-31-2012, 11:55 PM   #7
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Quote:
Originally Posted by redlinernyc View Post
well here's my input. On my 2006 600rr I had the Arrow pipe that looked like a limp penis and I hated the way it stuck out under the tail. So I got it shortened by 2 inches. Took it to the dyno to see if it impacted any power and I lost 3hp. The week before I just got it custom mapped. Weather conditions and humidity were the same, not to mention it was done by the same dyno tuner on the same dyno. Just food for thought.
based on your experience it reminded me I need to have all these test done with the stock pipe as well for the control. I will do the stock pipe with and without servo.
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-street bike
02 GSXR 1000(Red/Black/Silver)

-Corner tuckin, go fast humming bird
- Her name is PITA (Pain In The Ace)
07 CBR 600rr (Blue/Silver)
Galfer steel braided Brake Lines (Front and Back)
PSR click n' Roll shorties (brake and Clutch)
Shogun swing arm spools
Shogun no-cut frame sliders
Vortex Steel sprockets (-1,+2)
RK Gold chain
Yoshi Full RS-5 Stainless/Titanium/CarbonFiber

more to come!
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Old 11-01-2012, 01:00 PM   #8
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Old 11-09-2012, 09:06 PM   #9
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hmmm.... this will be interesting.
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Old 11-17-2012, 11:32 PM   #10
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subscribed for results of the test.

I doubt youll see any difference in power, only in sound.
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Old 11-29-2012, 03:32 AM   #11
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Please do remember there is a catalitic converter in the header.

Also isn't a exhaust servo to increase back presure? I honestly don't really believe in back presure unless there's a turbo, the back presure affects that more than the engine.
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