Cut off exhaust on Hayabusa? - Sportbike Forum: Sportbike Motorcycle Forums
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post #1 of 17 (permalink) Old 03-11-2006, 06:36 PM Thread Starter
 
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Cut off exhaust on Hayabusa?

My friend literally cut off his exhaust on his Busa. He cut both silencers and some of the pipe off and welded up a flange for both sides of the exhaust to exit under the right rearset. I argued with him for almost an hour that it is not good for the bike. He insists that lots of people with Busa's do it. I tend to disagree and I would think that he is at a high risk of burning some exhaust valves. The bike is incredibly loud. Probobally the loudest bike I have ever been around. I can't even ride next to him, and the sound isn't even a nice one. I can't imagine why someone would want to do this. Can anyone give me some feedback on this? I would like to show him what others think about the idea of this. I just don't want him to destroy his fairly new bike.
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post #2 of 17 (permalink) Old 03-12-2006, 05:07 AM
 
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The exaust provides back pressure to the cylinders. When you modify the exaust you mess up the back pressure, thus messing up the intake/exaust process which can mess with performance. I believe that is why most people with aftermarket exaust have the the ECU remapped or get a Power Commander with a special map made for the exaust. However im definatly not a mechanic this is just my best assumption based on readings.
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post #3 of 17 (permalink) Old 03-12-2006, 08:26 AM
 
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Quote:
Originally posted by slick1537
The exaust provides back pressure to the cylinders. When you modify the exaust you mess up the back pressure, thus messing up the intake/exaust process which can mess with performance. I believe that is why most people with aftermarket exaust have the the ECU remapped or get a Power Commander with a special map made for the exaust. However im definatly not a mechanic this is just my best assumption based on readings.
Seems like pretty good assumptions.

I would hate to have a really loud street bike. For several reasons. In fact, I short-shift a lot so I don't disturb people living close by. Motorcycles have enough "image" problems.
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post #4 of 17 (permalink) Old 03-12-2006, 08:46 AM
 
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AND to think HD is suggesting that riders start to "pipe down" the exhaust note of their personal bikes. Though some of us, with far more riding experience then other, are still riding with STOCK exhaust systems.

I have never heard of anyone butchering the exhaust system of their Busa like this fool has done. Still the longer you are in the sport/hobby of m/cing the more idiots you tend to bump into or hear about.
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post #5 of 17 (permalink) Old 03-12-2006, 08:55 AM
 
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Quote:
Originally posted by clutchslip
Seems like pretty good assumptions.

I would hate to have a really loud street bike. For several reasons. In fact, I short-shift a lot so I don't disturb people living close by. Motorcycles have enough "image" problems.
I almost always short shift, unless I'm on the highway or doing a decent take off. Ofcorse I live in a retirement comunity so they complain enough about me as is. I feel sorry for you steve not your friend. Its his fault if he ruins the bike but you have to console him and try not to laugh your ass off and say I told you so Your also stuck riding next to him. I cant stand riding next to HDs I would hate to be by him.

Sepias
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post #6 of 17 (permalink) Old 03-12-2006, 09:06 AM
 
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Hi All-

Slick1537 is absolutely correct how wholesale changes in the exhaust system (especially just hacking it off...) create significant changes to the important backpressure reaching the engine. Even if it didn't negatively impact the operation of the powerplant, it would just be incredibly uncomfortable riding that beast with all that annoying racket blasting one's ears. I'm talking to the point of causing permanent hearing damage. Take a look at some of the various earplug threads for background information.

Count me in as another rider who attempts to make as minimal a footprint out on the road as possible. I ride courteously and quietly, yet declare my space with proper lane positioning. We are all ambassadors for the sport, so all it takes is a few knuckleheads with incredibly obnoxious bikes and/or riding habits to undo our good efforts.

~ Blue Jays ~
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post #7 of 17 (permalink) Old 03-12-2006, 10:00 AM
 
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straight pipes are, when at full throttle, can reach 140 dB. My friends ninja 600 makes about 130-140 dB with his 4" straight pipe. People can hear him a mile away and it sounds not that bad. He has a full muzzy system and says he can notice a significant power loss with the straight pipe on.

Also, back pressure is important to the valves as it provides pressure for the valves to close on time. If you don't have then engine mapped correctly for the difference of exhaust flow, you could be seeping in exhaust gases back into the engine chamber and cause a reduction of power. But this is my understanding as I'm not an engineer.
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post #8 of 17 (permalink) Old 03-12-2006, 10:50 AM
 
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Quote:
Originally posted by JBaz

Also, back pressure is important to the valves as it provides pressure for the valves to close on time. If you don't have then engine mapped correctly for the difference of exhaust flow, you could be seeping in exhaust gases back into the engine chamber and cause a reduction of power. But this is my understanding as I'm not an engineer.


Yes its true. With a reduction in back pressure you have more air drawn into the combustion chamber then normal. This basically results in a lean burning effect as which we all know is damaging to an engine and thus the result of burned valves. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque. Which is why people sometimes equate back pressure with torque.
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post #9 of 17 (permalink) Old 03-12-2006, 02:47 PM Thread Starter
 
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I am a mechanic so I definately know that burnt valves could be the result of an open pipe. I told him that he at least needs a power commander to make is somewhat work properly. He says the bike runs smooth without the powercommander but I think he's full of it. I noticed that My bike even ran rougher with a D&D pipe eventhough I have a power commander because of it's straight through design and reduction in backpressure. Therefore a hacked exhaust couldn't possibly be any good for the engine. When he gets on it real hard then decelerates you can see some blue flames come out of the pipe. He told me that there could be no negative effects from doing what he has done. I can't wait until he blows up the engine and his fairly new hayabusa is junk yard material. I can tell you one thing, I wouldn't want to be the one on the bike at 12K+ RPM's when the combustion temp goes so high that it melts the top of the piston and then seizes the motor and then results in a rod being thrown through the crankcase into the side of my leg I guess time will tell, he will be crying when he has a useless bike
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post #10 of 17 (permalink) Old 03-12-2006, 03:13 PM
 
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Its gotta sound down right nasty. I pulled off my slip on to clean it and decided to see what my bike sounded like. It was loud and sounded like crap. I put it right back on. Have fun with the "I told you so"s

Sepias

P.S. send picks of the bike when the engine blows. I want to see the shaft through the side of the bike. It would make a nice poster. Take a before and an after. This is your busa... This is your busa in the hands of an idiot.
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