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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