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Discussion Starter · #1 ·
What would be the downside of a straight pipe on the grom? would it totally ruin the performance of the bike or would it increase performance? What would you have to do with a straight pipe to make it work with this bike?
 

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I would imagine without a tune it would just make performance worse.
 

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Might be roughly the same as you get a more free flowing exhaust, but without a tune it might not compensate correctly.
 

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1 - it would be annoying.
2 - you would lose torque due to the loss of backpressure.
 
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Yes that is exactly it tuning would bring out the best of the straight pipe. Another thin I would see as a downside is the noise level might be going up and sounding different. Be prepared to gain some angry neighbors. ;)
 

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Your neighbors will hate you, it's going to be loud as ever.
Im sure there will be some nice aftermarket exhaust systems that will have you being less inclined on going with a straight pipe
 
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its tough to say. with carbs bikes are very sensitive to these kinds of mods but with a fuel injecton system the computer would compensate and regulate the engine. the exhaust may provide some back preasure to help with exhaust scavenging but i dont see a strait pipe doing that much harm especialy if it has an oxygen sensor and its far enough form the very end of the exhaust tip to keep it from reading false data. id love to see a dyno run after break in and with and with out the muffler.
 

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I took the can off to spray paint the endcap, and just for fun, I started it up with just the straight pipe coming up under the seat. Honestly, I was surprised at how quiet it was. Of course, it wasn't whisper quiet like stock, but it wasn't all that loud either. It takes just a minute to take off the exhaust can, so try it yourself and see what you think. Then go from there.

Also, I have a hard time believing that it will ultimately hurt the power output. As long as the computer is making things happen right (stock tune or not) then it should be nothing but better for it. The best performance comes from an open pipe. Back pressure is only an issue when you're trying to make a streetable exhaust system act like a super free flowing open header system. Bottom line, open header wins every time, but with the right tuning, a full length exhaust system can come damn close. This is most obvious in cars where the exhaust system runs such a long length, and it's very noticeable and difficult when trying to tune a full exhaust system perfectly.
 

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Also, when tuning an exhaust system, it has nothing to do with backpressure; that is a common misconception. It really has to do with exhaust gas velocity and temperature. In an open header system, you have the ultimate performance, at high noise levels. With a properly tuned full exhaust, you keep exhaust velocity up as high as possible (which keeping temperatures up helps), and thus you can maximize the efficiency of it. You do that by manipulating the size of the piping to keep exhaust velocity up, not to put backpressure on the engine. On a two stroke, backpressure is good. On a four stroke, backpressure is bad. You are looking for a scavenging effect, so the exhaust system will be practically sucking the exhaust out of the engine.
 

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I wish people would stop quoting backpressure as a meaningful term. I mean no offense to those who say this word... Please do some research. Most of the time what you mean is that exhaust with no backpressure actually has no scavenging which is the correct word. Very rarely on a four stroke would you actually be looking for positive pressure in the exhaust pushing back on the valves/engine.
 

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There has to be baffles in the stock muffler that can be knocked out. People do it sll the time on other bikes
It's not baffles causing our power restriction, it's supposedly a catalytic converter. I haven't verified yet if it's actually a cat pipe, but there appears to be a large diameter catalytic converter near the back end of the header before it connects to the muffler mid pipe.

Once I buy a different exhaust I intend to cut open the factory muffler to show everyone what it looks like inside which will hopefully help people figure out how to (free) modify the stock muffler for more sound.
 

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Too loud. I did it and didn't like it.

[ame=http://www.youtube.com/watch?v=NWUxmt5bEkA&feature=share&list=UUZtNnNu7FQkBEYvoMxaHODw]Honda Grom with No exhaust, straight pipe. - YouTube[/ame]
 
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