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RyansToys
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Discussion Starter · #1 ·
I can't get the idea of a muffler below the engine with side dumps out of my head.

What are your thoughts on primary length, dumping into a volume from either side and exhausting on both sides?

Rough image of what I had in mind (SV650 engine... Rough..)



What would happen if you skip the muffler all together and dump straight down from the primary?

What sort of diminished performance might you expect if you dump into a muffler like the image? Does cyl 1 and 2 help each other? I haven't found anything online, but remember seeing that on car shows. Equal lengths are important..etc.
 

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With two pipes feeding into opposite ends of the same muffler like that I don't see a way for the cylinders to help each other with scavenging. I would assume that performance will be worse than even running individual straight pipes. If you're going to do an exhaust that exits under the engine, model it after the ones that Buells have. They tend to perform well enough and dump out the sides in front of the rear wheel.



Or start with a Suzuki Gladius header, chop off the junk after the 2-1 collector, and add a Quat-D style muffler.



 

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lɐʇuǝɯᴉɹǝdx&#4
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Using typical merge designs, cylinders do (under ideal conditions) help each other. The idea is that the 'front' of the exhaust pulse of one cylinder arrives at the merge just as the 'back' of another cylinder's exhaust pulse is leaving. That helps 'pull' the exhaust gasses from the cylinders, meaning the engine does less work pumping them out and the cylinder might even end up with below-atmosphere pressure when the exhaust valve closes. Its called "scavenging".

A design like above could maybe still have scavenging, since the effect depends on resonance as much as the direction of gas flow, but the effect would probably be weaker and harder to predictably tune for, perhaps going the opposite direction (ie, increasing back pressure at certain RPM instead of decreasing it). With a typical merge design, even at RPM where you don't have resonance, you still have the momentum of gas flow all going one direction, encouraging each header to empty as quick as possible.

I'm guessing there's a reason it won't work, even if the headers enter the can at the same end. If you could just dump the headers right into a can and avoid the extra weight of a merge and collector pipe, while still getting beneficial scavenging, race bikes would do it (to save weight) and manufacturers would do it (to save cost). They have the research budget to figure such things out.
 

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Keep in mind, your "vision" can also be tweaked functionally.

View your muffler from the top...
You could split your muffler diagonally, separating the two exhaust gases from eachother, but leaving the look you are going for.

Functionally, no different than dual exhaust. Maybe even put a smallish hole between the chambers... it would be the same as an "H" pipe.
 

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RyansToys
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Discussion Starter · #5 ·
Yeah, I was definitely considering separating the exhausts. I was very hesitant at first, but then started looking at shadow and harley exhausts... that are straight pipes... unequal lengths, and unconnected...

 

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lɐʇuǝɯᴉɹǝdx&#4
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Regardless of engine quality and balance, tuning headers for scavenging doesn't offer much benefit at low RPM. So if the engines redline is something like 5000 rpm, there's not much reason to worry about it, unless you have something like a 12 cylinder engine (lots of exhaust pulses despite low rpm).

Its also possible those pipes are tuned to match, but are not equal length. A straight pipe that's twice as long as a shorter one still 'looks' the same to the exhaust for this purpose, because it will resonate at the same frequency as the shorter one. AFAIK, the Shadow pipes aren't straight pipes - I think they hide a smaller pipe and muffler under a chrome heat shield / cover that looks like a straight pipe. There might even be a concealed crossover. Japanese cruiser exhausts are weird like that.
 

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yeah... generally MOST of those exhausts aren't actually straight through.

But yeah, completely separate is perfectly fine. The main trick is to have equal backpressure... which is easiest by making everything else equal. But pipes like that, can easily have equal back pressure while being different lengths. having everything equal is the dummy way to get the pusles ALWAYS opposite eachother... but it can be done with different lengths by taking the "wave length" into consideration... lots of techy stuff and calculations and shit. Just make them close to equal and call it good. ;)
 
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