Under-engine exhaust?

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Under-engine exhaust?

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Under-engine exhaust? - 2/1/2007 12:10:31 PM

HurricaneForce

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Just throwing this out there. Would it be possible to eliminate the exhaust can on a Hurricane by building a combination collector/muffler, kind of like a Buell? How hard would it be to get the proper backpressure and make it quiet enough? Here's a picture of what I mean. Obviously you would have to design baffles, etc. But would it be possible to do without hurting performance? I think it would clean up the look of the bike and cut 10 or 15 pounds of weight.

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RE: Under-engine exhaust? - 2/1/2007 12:49:06 PM

rrasco

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sounds prominent. i wouldnt do it personally cause i think bikes with small/non existant exhaust are ugly.

look at the new gsxrs, they have that tiny can on them.

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RE: Under-engine exhaust? - 2/1/2007 12:49:23 PM

michigan_313

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i've actually thought about this for quite sometime.

it will look good but suffer on performance in some places on the power curve. you will have to rejet the carbs. i "think", i cannot remember, but i "think" it causes a lean condition.

1. try this. run the bike without the midpipe/endcan. that should give you a good idea of how it will perform and how loud it will be. i've done this myself a few times for sh*ts and giggles.

2. to make an exhaust system quiet, you need volume. you need volume and some baffle in the can to absorb most of the exhaust wave before it reaches the exit of the exhaust. thus if you look closely at the Buell, it is a 2 chamber design in an "s" shape to get the most volume in the least amount of space or packaging. a Buell exhaust is rather large if you've never seen one up close. it's like putting an exhuast can and midpipe side by side and it would still be larger.

3. this mod is easy to do. however, the collector is not symmetrical. it's assymetrical, more to the right so the exhuast can route right side. you can chop the end portion of the collector out and reweld it to be symmetrical and then weld 2 tubes for exhaust outlets.

4. there are quite a few ways to get a larger exhaust volume to fit under the bike. just takes some imagination. just remember to leave yourself some room for the oil drain plug and heat shield between collector/exhuast combo and oil pan. the bottom of the pan will take a lot more heat from the exhaust if it all gets stuffed under the engine.

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RE: Under-engine exhaust? - 2/1/2007 1:10:32 PM

HurricaneForce

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Thanks for the advice, Michigan. I've run my bike without the can before, and it is very loud. I've never ridden it that way, so I don't know about power loss. I know Buell exhausts are large, but they are also for a v-twin. I don't know if that makes a difference or not. I was thinking about making a whole new collector, so symmetry wouldn't be an issue. I didn't consider heat, though. I know some cars have "glasspack" mufflers. Are they just packed with fiberglass insulation or what? And what does the glass do to noise and/or backpressure? I think that designing the baffles to prevent power loss would be the most difficult part.

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RE: Under-engine exhaust? - 2/1/2007 3:01:10 PM

michigan_313

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well, if you want loud, get "glasspacks" or as i call them "cherry bombs". it's just a straight exhaust, think motogp exhaust can, big pipe, little can, absolutely nothing in it, no baffle, no glass.

try to imagine putting the equivalent stock exhaust volume (midpipe and end can) under the bike. that's alot of volume and no matter how you or i package it, it will not fit. so, a compromise will have to be made. get as much under there as possible. you could make it an "s" shape and put a core in on the straight runs. there will not be a collector or sorts anywhere in the system.

in a regular exhaust can. the more packing that is put into it the greater the sound reduction. so in my case, i wrap the perforated core with fiberglass packing really tight with several layers to deaden the sound but keep the exhaust flow high.

if you take a look at some (ie. laser or scorpian) of the newer exhausts for later model bikes, you will notice that they have a removable baffle for "track" use. when you want to quiet the bike down, put the baffle back in. only thing is it is easier to redo fueling on efi bike than on carb bike.

so, take a ride on the bike around the block without the midepipe and can on. i know it is loud but it'll only be for a few minutes (try not to piss off the neighbors and attract the attention of local authorities). enough time for you to see how performance is with a lot less exhaust plumbing. that should give you an idea of your design parameters.

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RE: Under-engine exhaust? - 2/1/2007 4:22:36 PM

HurricaneForce

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What attributes of an exhaust system affect engine performance? I don't know much other than backpressure. It seems like with enough baffling and restriction, you could prevent a lean mixture. I don't want a loud system.

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RE: Under-engine exhaust? - 2/1/2007 4:28:17 PM

HurricaneForce

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Would you pack the fiberglass in the middle of the exhaust chamber (like in the second chamber in the picture) or line the baffles with it (like on the last baffle in the picture)?

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RE: Under-engine exhaust? - 2/1/2007 5:01:39 PM

SIRR1

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If I remember correctly there is a minimum length of pipe need to obtain maximum HP.

I think it's 27 inches from exhaust port to silencer.

If you look at the Buell they use curves and turns to get to that minimum length.
http://www.buell.com/en_us/bikes/ulysses/xb12x/features.asp

By cutting the cane head pipes off under the motor and welding on a Buell type muffler under the motor you won't have enough length on the head pipes to obtain good hp.

I think you will run into performance problems, I could be wrong but I think the head pipes will be to short.

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RE: Under-engine exhaust? - 2/1/2007 6:07:23 PM

michigan_313

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yes, minimum exhaust length is an issue. each engine is different so i do not know what it is for specifically the 87-90.

another question is how do you get the packing into a shape such as the one shown. will it be packed then welded shut or will there be a way to take it apart and repack it when the packing no longer can perform?

again, ride the bike around without the midpipe and exhaust. the performance will not be far off from your design as far as size goes.

as for baffling, i do have a couple ideas, one doesn't even require any. i'll have to attach a couple of drawings.

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RE: Under-engine exhaust? - 2/1/2007 6:16:10 PM

cjp48

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Based on the sketch you have there you may be adding more pressure on the system than the stock pipe and silencer has. From an acoustical standpoint, you'll need some decent chambers to absorb the noise.

I am not studied in the performance aspects, but its likely that the design of such systems is a little more involved than we think. Noise, Pressure and Flow considerations aren't always intuitive. It would certainly look cool but it may not gain any HP.

Good luck,

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