Unrestricted and quiet, 2 words never used together.

[madprofessor]

Fairly quiet, yet 99% unrestricted exhaust: I custom built one with an educated guess after drawing it up as a schematic plan on a notepad. Uses the basic principle of noise-cancelling headphones, that matching sounds running into each other will cancel each other out. Mine has 4 full 180-degree switchbacks in it, with the sound bouncing back and forth off the 5 bulkheads from start to exit, but so oversized that there's basically no restriction at all. It's on a hot-rodded up Predator 212cc motor, where it comes off of the head's D-shaped exhaust port with a 1" round tube that covers the entire opening, then angles away about 4" long to the side of a 3" I.D. length of car exhaust piping, right at the beginning of it. Total length without the rectangular box tip at the exit is 13". There's a 1&1/2" expansion section to start, then a 5" resonator section, then another 5" just like it, then a final 1&1/2" section to center the exit flow. The sound is a deep rumble somewhere between a lawnmower and a leafblower, but the power basically doubled immediately, even smelled raw gas in the exhaust now, has more than it can even burn until I advance the timing 8.4 degrees (next mod). Hi-flow cone air filter, billet venturi intake, and racing carb jets weren't being allowed to perform when factory exhaust was in place, so all the mods suddenly starting working when new exhaust was fired up on this custom minibike, doubled the power, kept flipping over backwards, snapped the chain, crazy. With CVT (torque converter) and pushing at least 12 hp. plus, it's just too stupidly powerful and dangerous to really ride, even with the built-in adjustable wheelie bar. Exactly what I was trying to build!!! Took a year, scratch-built from raw plate steel and tubes. Only wanted to build it, not ride it. Plan to sell it, then do the same thing scratch-building a track/trail wheelie-popping go-kart. Note: Used about half a tube of welding rods on that exhaust system!

 

[Hellion]

Hey professor!

Videos please. Got before and after videos or a straight pipe versus yours?
We gots peeps very much interested in some nice quietude.

 

[madprofessor]

Will try live sound video.........

Only recently been learning how to do all of this picture transferring and uploading and such. Tried my little camera for video, but the sound was too quiet. Will try with my phone, if it's good then I'll post what it actually sounds like. Just remember the principle of "equal and opposite reaction" to cancel out noise. I'll definitely post a picture of my penciled schematic showing how mine works.

 

[JTSpeedDemon]

Cool!
That's real impressive!

We gots peeps very much interested in some nice quietude.

^^I'm not in that group! Not interested in quiet, just mad amounts of power. Muahahaha...:arf:

 

[Texan]

Pretty nifty, I saw this bike on ebay a day or two ago. Wasn't looking, but dang google and their ad placements

 

[madprofessor]

Let it breathe, really breathe!

Hey there JTSpeedDemon, about that mad amounts of power...…….Each step of horsing up my motor was clearly working on each test ride after making changes, but like I said, the real power didn't come on until the exhaust got freed up. If noise is okay with you, I recommend using the largest I.D. pipe you can get to fit on the blank exhaust flange (about $8). Mine's a 1" that I welded on that's so tight between the flange bolts you can only use a box end wrench on the nuts, they almost touch the tube. The factory "box" muffler isn't just stoppered up by its guts, I checked to see if a dime (10 cents) would even drop into the factory tube, it won't. So it's strangled before it ever leaves the head! I don't know the true I.D. of those "header pipes" you can buy for $20-$30, but don't settle for store-bought if you can do bigger. Either way, a spooled up straight-piped 212cc can be heard 3 blocks away.

 

[Hellion]

^^I'm not in that group! Not interested in quiet, just mad amounts of power. Muahahaha...:arf:

Well, thanks for your two cents there.

Why would you even feel the need to comment if noise is your thing?

 

[madprofessor]

JTSpeedDemon posted because he likes "mad amounts of power" and it really is a novel thing for somebody to get that and quietude together in the same flow of gases. Clearly he'd sacrifice the quietude to get the power, but with my (blind educated luck) rig he could still have both.

 

[Kartorbust]

You should get a decibel gauge and compare the stock muffler, straight pipe, and this creation of yours and see how they all stack up. Do it at idle, half throttle and full throttle.

 

[Budget GoKart]

How do i make one my yerfdog is getting a twin briggs soon so if i cant figure out a muffler its going straight piped

 

[Hellion]

Do individual straight pipes on that twin, Budget. Don’t do two-into-one or something.

They sound so wonderful on YT videos people have done, like carsandcameras and those guys with the mudder riding lawn mower/ATV things.

 

[Budget GoKart]

Yea thats what i was going to do individual straight up like rbg but i kinda want a muffler considering how loud its going to be

 

[itsid]

Okay first:
with none of the following I do say it's a bad exhaust you made;
I just want to be precise on "definitions" and give you some hints of what professional mfgs do.

restriction is reduction in flow speed!
Ideally NO single exhaust should limit the throughput of the intended engine (most do by accident if at all)

A 'tight' 90° bend in your exhaust is already a noteworthy restriction,
the particles on the inner radius will jet straight bump into the ones coming from the outer radius eventually hit the wall to be stopped, and then carried away by
the stream that already changed direction...
a single bad bend like that can reduce flowspeed by 10-15%
That's why ideally you want a large bend radius to lessen the restriction
even of a simple tube -otherwise unrestricted- exhaust.
(hence pipe fitting exhausts may look cool [cough] but do nothing in your favour otherwise)
The reason you see getting steel pipes discoloured at the bend is the
heat from all the upset molecules hitting the wall turning kinetic energy to heat!
from a different thread but makes a nice example:

since it's about the least amount of pipe someone should mount to an engine to prevent his leg being fried (also: nice radius.. still too narrow for not restricting the flow ... obviously)

A most simple yet effective std motorcycle exhaust is a straight forward pipe,
with the last section of the pipe crossdrilled a few dozen times,
those holes covered by a fibreglass or steel-wool packing amterial and then wrapped in another tube to contain the fibres (and some air pressure)
(I think this is what you refer to as an expansion chamber... it's not it's a muffler or a resonating chamber (packed or not?).. nevermind)
And that is quiter and less restrictive than if you leave the packing material away.

Again molecules escape through the cross drilled holes and bump back into the exhaust stream
slowing the stream down (making it more quiet)
with paking material molecules can escape less easily and they get slowed down inside the labyrinth of packing material and are when they eventually bump back into the stream
they have less momentum and can slow the stream down a bit less
(thus being less restrictive and since the resonance is muffled by the packign amterial it's still quiter)

Sidenote: that's how the stock tube flathead briggs mufflers used to work and how the RLV muffler you likely find too restrictive works as well IIRC

now one 90° bend in the exhaust stream is already a severe restriction
and you have 4 180° switchbacks.. (720° with radiuses close to zweo I assume)
99% unrestricted... THAT'S A LIE!
I'd say you have ~43% of your original exhaust flow speed at the end of that,
sooo 57% restriction (no wonder it's quiet)
adn with what you called an expansion chamber it's maybe even at 60% or more..

essentially what you could've done instead is to buy ANY high volume stock motorcycle muffler
(say from a 1300cc sportsbike) it's dimensioned for the equivalent of 6 predators running at 13000 rpms or more depending on the originating bike
so a single 212 at half the rpms would barely be recognized by it
it'd be suuuper quiet and It'd be far less restrictive as well I bet.

Some motorcycle exhausts use two 180° switchbacks (usually combined with a pressure trap)
and those are the WORST when it comes to restriction...
motorcyclists of the sporty type HATE them and they get rid of them ASAP.
you literally made one twice as "bad"

Again, I'm not saying that your exhaust is indeed bad .. with large enough inner diameters and the allowance for a big enogh troughput, it it like able to handle the few cups of hot air per minute rather easily...
And if it works for you.. you did well; but it's not a well thought through design at all.
and it's massively restricting.. way more than a RLV muffler.

'sid

 

[madprofessor]

itsid: Appreciating your definitive numbers, but you must not have blown up the photos of the internal parts to see what's actually there. As stated, the outer body is a 3" I.D. by 13" long piece of exhaust piping, fed into by a 1" I.D. tube (bigger than D-shaped exhaust port) coming off the head. This is "pie-slice radiused", closed up, and welded, in 9 places to achieve a total angle all combined of maybe 90 degrees over the whole 4" length. You can see this in the left side underseat photo.
On my planked worktable outside you can see the dimensions of the inner tubes, which are a pair of 1.75" I.D. by 3.5" long each, and a middle one 1.75" by 7 " long, and see the 4#, 3#, and 1# hammers and the I/2" cold chisel and #2 flathead screwdriver used to reshape the ends of the tubes within each 5" resonator stage to fit with each other.
Each of the 5 bulkheads (includes the 2 end ones) are 100% welded solid, as are the inner tubes through the bulkheads they penetrate. The sequence is:
Ragged gases leave D-shaped exhaust port of head, get gently straightened out and traveling forward by 4" long curved tube that's 1" I.D.
1" round expands into 3" round by 1.5" long chamber.
1.75" by 3.5" long tube carries gases into 3" by 5" long chamber, with the reshaping of the inner tube reducing its square area from 2.4 sq.in. to approx. 1.8 sq.in.
Gases blossom out 1.5" shy of next bulkhead to fill all available space inside of 3" chamber, and migrate back to where 1.75" tube opening waits 1.5" below the opposite bulkhead, finds their way inside.
1.75" by 7" long tube carries gases into next chamber, sized from 1.8 to 2.4 to 1.8 sq.in. along the way.
Gases again blossom out to completely fill 3" by 5" long chamber, repeats as above.
Gases blossom out of 1.75" tube into 3" by 1.5" long chamber (translating from the side to the center), and exit via 1.25" by 2.25" O.D. rectangle box tip about 1" long.
Work your math on that, and when next over at my shop I'll video the actual volume of the system's output, try to post it here. The math will back up that the performance can't be improved in any way noticeable by removing my so-called muffler, and the audio of the video will back up the noise cancellation effect. Don't have a decibel gauge, or a straight pipe header to try, and won't reinstall factory muffler just to prove a point.
This entire machine has been scratch-built from the ground up out of raw plate steel and tubes without the benefit of a lathe, drill press, radial saw, or any other machine shop equipment. It's all been just me, a 4.5" angle grinder, a 120v. stick welder, a 1/2" drill, and a bunch of hand tools and know-how. Apologies if any machine shops are offended that they don't impress me as much as the folks who do it all by hand.
BTW, did I mention I'm not some young kid trying to figure things out for the first time? I'm a 61-year old career HVACR tech retired on disability, no money or desire to buy any generic factory stuff, and the "Holy Garage" is my shop at All Saints Episcopal Church. A little respect, y'all.

 

[Dingocat]

I'd like to hear it run if you wouldn't mind.

 

[madprofessor]

BTW itsid, while "reduction in flow speed" does indeed indicate a restriction in the applications we're talking about here, since you're wanting to "be precise on definitions" please don't lead anyone astray by being less than precise. You can take one of those straight-up open header pipes people use, weld it to the side of a coffee can, punch a 3" hole in the end of the can, and even assuming a 1" ID pipe you'll get a "reduction in flow speed" out of that hole by about 88% without any decrease in volume or power. That's changing 0.785 sq.in. of the pipe opening to 7.065 sq.in. of the can opening, of course there's a reduction in the flow speed. There's far more to the aerodynamics of restriction than simply speed, packing, baffling, etc. BTW, does your all-uppercase statement about my exhaust "THAT'S A LIE!" mean you're yelling at me? Just can't keep up with all this modern-day computer hoopla.

 

[Budget GoKart]

I wanna hear i dont care about restrictions honestly i just want my twin engine to not get me in trouble with the neighborhood...

 

[karl]

To avoid walls of text,

without a flow meter on the inlet and outlet , and a known amount of cfm moving through, any data presented for restriction is speculation

Maybe an accurate dyno , and many controlled tests with a decibel meter could provide some data to compare.

But as sid said, A free flowing muffler off a motorcycle will most likely provide similar or better results.

Experimenting and and being creative is great fun, but presenting data with no proof is misleading

 

[itsid]

BTW, does your all-uppercase statement about my exhaust "THAT'S A LIE!" mean you're yelling at me?

No with texts that long I just get too lazy to type the
"[B]emphasized statement of choice[/b]" at times
so a quick lowering of the pinky to the shift key must stand in as a shorthand for emphasize (talking "bold" is usually talking "loud'ish" which is close enough)
call it a quirk

Now.. I'd love to be "precise" and if you read a few of my prior posts (good luck with that ) you'll see that I am indeed the number fanatic in this asylum.
Unfortunately there is sooo much to consider with fluid dynamics that I know just enough about it to say that I do not know enough about it to be precise..
hence I'm vague on the details.

Since frankly, how are the tube ends treated?
rounded, ground flat, chamfered?
big difference for fluid motion.
is there a gap between the crushed tubes or not, and if how big;
is the gap uniform or as 'about'-ish eyeballed as the crush of the tubes look?
is the divider plate fully welded or spot welded, is it perfectly straight or as crooked as in the "not yet mounted" photo...

Are the insides of the tubes treated or not (polished, sharkskinned, brushed, crosshatched)
how does the welds look like?

And while any single miniscule difference might not make up for a dramatic change,
but all the things combined DO! [oh look.. once again... hehe]

fluid dynamics winged are never precise enough for me to label them such, and even with a simulator I'd not be confident to get all the tiny little details correct in order to make a sound and "precise" statement.
So even that only get's me not more thn a very good educated guess.

So..why bother, when all I'm trying to say is that your claim
("99% unrestricted") is definitely incorrect (by a huuuuge amount)

Since when does HVAC stands for exhaust expert?
that's like saying a engine mechanic is a good watchmaker since he worked with gears too.

Again, I don't know how well your exhaust performs..
how could I.. it might be really good or just okay..
I doubt it's bad tbh.. but it surely is not one percent or less restrictive

'sid

 

[madprofessor]

Trying to answer questions......

I'll try to answer those very valid questions posed above...…..
First, "99%" cannot possibly be dyno-accurate, aerodynamics will tell you that, so my apologies. I'll revise just to say that the gross oversizing, lack of any bends, and overall area to expand basically negates the individual 1 of 4 pulses of a 4-stroke exhaust, valve lift duration notwithstanding on that 1 of 4.
Tube ends are all nearly identical. Ends are cut by 4.5" cutoff wheel, and ground smooth. Looking closely at pictures almost shows that ends remain near to original curve on the sides that are "outboard" of middle, while being graded down to "pillowed" or "figure 8" configuration where two tubes are passing by each other by 2" in the middle, and are tightly together there for that 2" common space. Bulkheads are all 90 degree even and symmetrical placements. All welds are 100% airtight, includes header connection, all internal and external bulkheads to 3" shell, and all internal tubes at bulkhead penetrations and abuts. The "divider plate" mentioned is actually only the center bulkhead. Looking closely at the pictures shows that the internal tubes as laid out in "exploded view" are sitting there in the bulkheads they penetrate, and those are 1.5" inside of each respective end of the 3" shell, so including the end bulkheads there are actually 5 altogether, 3 internal, 2 external. Again, all are welded airtight. The insides of the 3" shell and 1.75" tubes remain the auto parts factory finish as purchased from (Blank) Auto Parts. Finish on the 22 gauge sheet metal bulkheads remains as store-bought from hardware store. Oops! There's another finish. When spray painting the exterior with VHT (Very High Temperature) header paint (1800 degrees) I sprayed some shots into the box tip, so that you only see black if looking inside. As to what the welds look like, everything external has been ground smooth with a 4.5" angle grinder using a wheel and a flap disc, while the internals are as welded minus a thorough treatment with a chipping hammer, and all are the very heavy welds of a guy who doesn't care how many rods he uses up. About when HVAC stands for exhaust expert, it does not. HVACR Is Heating, Ventilation, Air Conditioning, and Refrigeration, and does not just cover Grody-Ruder guys coming to your house to shoot some "freezonn" in your A/C system. In my case it covers a tech at the very top of his field upon retirement, taking care of 500-ton chillers for hospitals, Navy-spec air systems onboard nuclear submarine tenders, entire rack systems for all refrigeration in grocery stores, designing and installing air movement systems in national breweries, not to mention winning 5 times out of 5 when challenging international manufacturers on the incorrectness of their HVACR parts. Exhaust expert with muffler burns and grease in my eye, certainly not. Physics expert in aerodynamics and fluid dynamics with more than 20 certifications in the field, you betcha.
BTW, going in to my shop today (The Holy Garage), have to prep for the Sunday Breakfast where I feed the whole church every week (Volunteer Sexton and volunteer MOAS Kitchen Manager), will record the output of my creation for all to hear. Good timing, the #35 chain is still snapped, can rev it up now without the clutch grabbing. Will post when I figure out how.