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Post by ibtrikin on Mar 15, 2013 16:15:01 GMT -5
I ordered an Emgo shorty muffler to replace my stock muffler which is falling apart. I ordered it because it is 12 inches long, which is the right length for the trike. When it came in, I noticed it's a pretty open design. It is baffled, but it's pretty much a hollow 3/4" tube through the center. Think it will have enough back pressure, or do the 150s even benefit from back pressure?
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Post by prodigit on Mar 15, 2013 16:19:41 GMT -5
Back pressure is what you want to avoid, to get better gas mileage.
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Post by terrilee on Mar 15, 2013 16:57:49 GMT -5
now we all know im NOT a mech 
but dont 2T's need lots of back pressure
and dont 150's need some back pressure
or am i totally wrong?
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Post by prodigit on Mar 15, 2013 17:12:55 GMT -5
I presume the 150 he talks about is 4 stroke.
And ultimately you'll want to avoid back pressure on all scoots. However, there will be no sound damping, without some form of back pressure, so some of it is unavoidable.
Basically the pipe going into the muffler (the pot), releases the gas in such a way that it sounds very sharp to the ear. The muffler then has those sharp sounding sounds bouncing to and fro inside of it, weakening these sharp frequencies, so that at the exhaust tip, the sharp noises are greatly diminished, and only the middle and low tones come out; which are less harmful to the ears.
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Post by tvnacman on Mar 15, 2013 17:36:55 GMT -5
I have a proformance muffler, I have to wear ear plugs. You need some back pressure for low end tork.
John
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Post by prodigit on Mar 15, 2013 17:44:18 GMT -5
I have a proformance muffler, I have to wear ear plugs. You need some back pressure for low end tork. John explain exactly what you mean? Because as far as I see it, as soon as the gas escapes the exhaust valves, it has nothing to do with performance of the engine anymore. Back pressure causes burnt gas to be remnant in the cylinder, degrading performance; but in order to run your engine optimally, it's best to actually release the exhaust gas in a vacuum, if that ever where possible. because of the pulsing nature of the exhaust coming out of a gasoline engine, the little exhaust pipe coming from the engine, actually provides something that comes close to a 'vacuum' on the engine; but I'm sure there are others that are better equipped with that knowledge to explain how this works. |
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Post by tvnacman on Mar 15, 2013 20:34:00 GMT -5
pro there is a better way to answer your question , I can not get it into words .
John
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Post by skuttadawg on Mar 15, 2013 23:16:39 GMT -5
The exhaust does play an important factor on performance with more on a 2T . Stock exhaust should work fine unless the packing or tubing gets clogs resulting in a restriction . When I put on a BBK and MMG pipe is was slower on takeoff since its an open exhaust with no baffle , loud enough to make my ears rings if near a large bus or building as it echoes at high RPMS . I did have a higher RPM and top speed as stock most of the time it would hit 45 but sometimes 50+ . With a BBK and pipe I go way beyond the 50 MPH mark as that is as far as it is numbered but sends the needle to where 65 or 70 would be
When you install a Uni you get more intake flow but can bottle neck somewhat with a restricted exhaust . An engine is like an air pump the faster you can get air in and out of it the faster it can run . Think of it like this when you have congestion in your lungs you can not breathe as good as when normal . Same principle applies to engines
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Post by tvnacman on Mar 16, 2013 5:03:48 GMT -5
Skutterdawg , what State are you in ? I'm thinking CT for some reason . Are you far from NYC ?
John
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Post by ibtrikin on Mar 16, 2013 10:05:34 GMT -5
Thanks for the input guys. I'm gonna try it out. I just wanted to know it wouldn't damage the engine before I started cutting and welding on the pipe. If it doesn't work out, I can order a new exhaust. I'll only be out $27 for the Emgo, so no big deal.
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Post by twistedburnout on Mar 29, 2013 21:13:19 GMT -5
Lool! Back pressure is not a factor?
For all of you who just stated such wrong information please just sit back and get edified for a moment.
Your exhaust must have an inlet and an outlet pipe that is the same size (diameter) as your front pipe and your tail pipe. Your front pipe and your tail pipe should also have the same diameter. The rest of the exhaust system is much more complicated as you need consider back pressure, your engine's power band, and your engine's maximum usable RPM.
The amount of back pressure produced by the exhaust system is crucial as too much back pressure will have a negative effect on your engine's top-end performance as it will restrict the flow rate of the exhaust gasses at high RPM. The result would be the engine not being able to expel the spent exhaust gasses fast enough to prevent spent exhaust gasses from contaminating the fresh air/fuel mixture that is drawn into the engine on the next intake stroke. Ultimately, this will result in reduced engine power! Therefore, attaching a little 1-inch pea-shooter to your engine instead of an exhaust system is not such a good idea! But then neither is fitting a 10-inch sewage pipe. If the exhaust pipe is too large, you will get reduced flow velocity of the exhaust gasses. The flow velocity of the exhaust gasses assists with the scavenging of the spent exhaust gasses as well as the amount of air/fuel mixture that can be drawn into the combustion chamber on the next intake stroke. This is because the flow velocity of the exhaust creates a low pressure immediately behind it that sucks more gasses out of the combustion chamber. The trick is thus to get the back pressure just right.
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