Stretch and I built a custom exhaust setup for my rally tractor, Chaos...
The dual exhaust is brought into one pipe using a custom header/collector. The cutout is built from the butterfly out of a carburetor. The straight pipe goes right out the back, and the silent pipe goes through a muffler before rejoining the tailpipe.
Pretty much a totally useless modification (unless you are dealing with noise ordinances), but way fun to come up with an idea like this and see it to completion.
Proud member of the Mower Cycle Gang... aka the "Mowrons!"
My build (Chaos is one of 3 built like this) Chaos Build
I friggin love it almost enough to build my own then come over and have you guys rebuild it right! lol Cant wait to hear what it sounds like in a few weeks
camomanusa Member
2014 Build-Off Entrant
2014 Build-Off Entrant
Age : 25 Join date : 2013-09-15 Points : 4579 Posts : 467 Location : Greensburg, PA
Very cool. Only thing I'd be wondering about is trying to balance the A/F mixture so it's okay in both settings. Fair bit of restriction in the "quiet" part of the system, starting with that 90° tee fitting. Awesome idea tho!
Ah, it's a rally mower, not a race car! Completely stock carb.
I'd call the dash lever a mute lever. When you close the exhaust, it's darn quiet at the rear. Reving the engine doesn't make any difference, it's still quiet...
And OMG, did I have to do some thin steel welding... That exhaust is freaking like a rock.
Those welds aren't as bad as some I've seen! I still don't know why most guys on this forum swear by flux core wire and then don't clean their welds afterwards.
Be careful not to breathe the fumes when welding galvanized pipe. Bad stuff.
On the welds, I've gotten pretty good at sticking thin steel together, just not in a pretty way. .035 wire, on the lowest setting of a miller 220. I do have a cheap 110v mig welder I could try for the thin stuff, but the big one runs very nice.
Angchor wrote:
Stretch44875 wrote:
That exhaust is freaking like a rock.
And I have another question...
Just exactly how -does- a rock, 'freak'???
Very slowly.........
Not sure on the butteryfly. But it is downstream some. Most times it will be open. Very smooth action at the moment, see how it does.
Well now not to beat a dead horse or anything... I am wondering what exhaust is better, dual straights or a 2 into 1 header, or dual straights with a crossover pipe?
T-Dub13 Established Member
500+ Posts
500+ Posts
Age : 55 Join date : 2013-12-06 Points : 4572 Posts : 540 Location : Central MA
Well now not to beat a dead horse or anything... I am wondering what exhaust is better, dual straights or a 2 into 1 header, or dual straights with a crossover pipe?
For performance on a V-twin (taking notes from the Harleys I've built) I've seen the best dyno numbers from a 2-into-1 exhaust. The length of each header should be in tune with the cam (more on that in a minute*), and the collector diameter equal to about 1.5x the single header diameter or slightly larger.
*If the cam being used has a long duration and (most importantly) a lot of overlap, then the tuned header length becomes critical. The stock B&S cams don't have enough of either to make the header length come into play.
So, just build the exhaust to fit the chassis and have fun with the tractor. I've noted that the 2-into-1 exhausts typically sound best as well, especially with a glass pack muffler.
ZSmachines Member
2015 Build-Off Entrant
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Age : 25 Join date : 2014-08-27 Points : 3992 Posts : 221 Location : PNW
Oh, ok, thanks! i am talking about my oppy, so i dont know if it would apply to the same principles as a v twin, but i am in dire need to redo my exhaust. i think that i will go with at least a 2 inch pipe. will that be big enough?
T-Dub13 Established Member
500+ Posts
500+ Posts
Age : 55 Join date : 2013-12-06 Points : 4572 Posts : 540 Location : Central MA
Yeah, same principal for the oppy I'm pretty sure. Think of it as 1/2 of an old school VW Bug motor and look at their exhausts... The high performance ones run 4-into-2-into-1. Same for Subaru boxers.
What size are the EXH ports? I'm assuming about an inch... So go with the matching ID header pipes and into a 1 3/4" collector.
The nice part about that is if you have a 1 3/4"" collector, you can just clamp on a Cherry Bomb!
A great trick I've used is bicycle frames and forks for building headers. The BMX forks are thin walled tubing about the right size and have a curve built in! I have a thread in here somewhere showing that I think...
Hows this holding up? I was thinking about a 2 into 1 setup on mine with a cutout. Is the butterfly brass or steel with some junk coated on it? No leaks or anything?
Subject: 
May 4th 2014, 1:36 pm
almost enough to build my own then come over and have you guys rebuild it right! lol Cant wait to hear what it sounds like in a few weeks
