Exhaust Question

[02ninjaeastbay]

My stock muffler is pretty well damaged, to the point that it fell off the other day. I've heard both ways, but is it damaging to the valves to run it with no muffler? I have noticed that the bike idles at about 800 rpm vs the normal 1300 or so. Please help, I want to know if I can ride it until I get a new exhaust or not. Thanks!

[kkim]

with no muffler on the end, you have less back pressure.... less back pressure... more flow.... more flow... leaner running engine... too lean running engine... possible burned exhaust valves.

if it were me, I'd ride it very little until the mufflers were replaced/repaired.

post up some pics of the damage and the connection point to the pipe.

[wayanlam]

im not sure if the reduced back pressure might cause any damage/problems with the bikes engine, but besides that, the bike will sound REALLY loud (a harsh raspy bad type of loud), and runs really badly when the stock muffler is removed. i drove around the corner and back from my house a couple times without the muffler when i was in the process of changing it out with the AreaP one at the time i think, and it was not pleasant at all.

if you have no other option, do it... maybe one temporary option/solution would be to stick a slightly more restrictive pipe on the end, so that there is a little more back pressure? would also avoid the bike running too lean.

im sure there are others with more experience who might be able to give a better reply to your question.

[kbryant]

Originally Posted by 02ninjaeastbay

My stock muffler is pretty well damaged, to the point that it fell off the other day. I've heard both ways, but is it damaging to the valves to run it with no muffler? I have noticed that the bike idles at about 800 rpm vs the normal 1300 or so. Please help, I want to know if I can ride it until I get a new exhaust or not. Thanks!

Damaging valves for that reason is primarily a myth. Obviously if the exhaust was 1 inch long and the atmosphere had almost direct contact with your exhaust valves while open in the exhaust stroke; yes, that could cause a problem over time . I've tested and tested and tested this "theory" over the years on so many engines I've lost count. It does not occur simply because you do not run a muffler.

As a whole, your engine needs a certain amount of backpressure to perform properly. The exhaust system and it's proper design supplies this. Whether it has a muffler or not, it still provides an amount of "backpressure". In your case, will it run very well? Not likely. Your engine is not tuned to run with an "open" exhaust system. And even if you were able to "tune" it correctly, it still would not perform as well (for a host of reasons).

So... the damage you may do to your engine is related to Air/Fuel (Jetting) and running lean, more than not running a muffler. But do yourself, your neighbors and your engine a favor; replace the muffler and/or get a new exhaust system.

[kkim]

You a politician or sumthin'? How can you answer the question w/o answering the question? If this answer came from anyone else, I'd be , but in your case, I will .

In your testing, did you find the exhaust flowed more or less freely without the muffler? After I answered last night, I did some searching and it seems the pipe length to the point of the muffler had an effect on whether the system w/o the muffler flowed more or less efficiently... or does it become more RPM dependent at that point?

Thanks for responding to this thread. As always, your knowledgeable input is highly appreciated.

[CynicalC]

Where in the east bay are you? I'll be taking off my stock exhaust soon. It's not mint but it's low mileage.

[kbryant]

Originally Posted by kkim

You a politician or sumthin'? How can you answer the question w/o answering the question? If this answer came from anyone else, I'd be , but in your case, I will .

In your testing, did you find the exhaust flowed more or less freely without the muffler? After I answered last night, I did some searching and it seems the pipe length and diameter to the point of the muffler had an effect on whether the system w/o the muffler flowed more or less efficiently... or does it become more RPM dependent at that point?

Thanks for responding to this thread. As always, your knowledgeable input is highly appreciated.

It's a skill honed through-out the ages....

Anyway.. Flow is somewhat dependant on the muffler and core design (among other things); henceforth it may or may not "flow" more freely. Alas, exhaust dynamics is not as easy as just increasing "flow" (I wish it was that easy...). Pipe length to the muffler is critical, as is what happens at that particular termination point in the system. When you then add the muffler, depending on diameter, length, core diameter, core length and exit tip length to the overall "tuned" length of the entire system, the results will tell you if you changed/improved the "efficiency". The "efficiency" equation includes whatever RPM goal you were trying to attain.

To increase Volumetric Efficiency, we simply think of an engine as a pump. To increase the "pumping" affect, so many things have to be considered simply based on the potential of the subject pump (engine, exhaust, intake, rpm, given goal). "Flow volume" is not the same as "Flow velocity"; and we consider both equally. Same with looking at "Wave Tuning" and "Inertial Tuning". The more we can create an efficient pumping affect by all these things, including vaccum and interia to our benefit, we create a better exhaust product. All this happens through set standards we know from experience. Then couple it with Flow Bench testing, Dyno testing, Road/Track testing, Sound testing and A/F testing based on whatever the goal was in the first place to see if your satisfied or not with the results.

Look, if we are ever going to open another division on the Big Island, you'll need to know these things. There will be a test for you tomorrow. Study up grasshopper.

[kkim]

Originally Posted by kbryant

It's a skill honed through-out the ages....

Anyway.. Flow is somewhat dependant on the muffler and core design (among other things); henceforth it may or may not "flow" more freely. Alas, exhaust dynamics is not as easy as just increasing "flow" (I wish it was that easy...). Pipe length to the muffler is critical, as is what happens at that particular termination point in the system. When you then add the muffler, depending on diameter, length, core diameter, core length and exit tip length to the overall "tuned" length of the entire system, the results will tell you if you changed/improved the "efficiency". The "efficiency" equation includes whatever RPM goal you were trying to attain.

To increase Volumetric Efficiency, we simply think of an engine as a pump. To increase the "pumping" affect, so many things have to be considered simply based on the potential of the subject pump (engine, exhaust, intake, rpm, given goal). "Flow volume" is not the same as "Flow velocity"; and we consider both equally. Same with looking at "Wave Tuning" and "Inertial Tuning". The more we can create an efficient pumping affect by all these things, including vaccum and interia to our benefit, we create a better exhaust product. All this happens through set standards we know from experience. Then couple it with Flow Bench testing, Dyno testing, Road/Track testing, Sound testing and A/F testing based on whatever the goal was in the first place to see if your satisfied or not with the results.

Look, if we are ever going to open another division on the Big Island, you'll need to know these things. There will be a test for you tomorrow. Study up grasshopper.

so, from what I'm reading, I can just make up an exhaust in my garage? sounds to me like it's just some tubing and with a muffler clamped on the end, right?

thanks for the schooling... I've always recommended not running without the muffler for fear of engine damage. From what you've posted, it can possibly lead to engine damage depending on the particular circumstance with regards to how lean the jetting was before removing the muffler and where that tubing length terminated with regards to the inherent flow characteristics of the system installed? short version... it's a crapshoot?

sorry, not on the Big Island... over on Kauai. And if you ever open a facility here, count me in, though I'd like a job where I could just sit back and harass the secretaries, please... much like the position you hold.

mahalo for sharing your knowledge.