Exhaust What did I do? TLAR exhaust mod?

Urban Fatbiker

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Finally running 32:1 mix, thought I had it performing pretty good.
Decided it was time to do something with the cheesy B&S stinger and crappy deflector I added to my banana pipe. I needed it longer too.

Did some butt dyno tests first, to have a reference. Couple of runs down my street for a baseline.

Took stinger off, raw banana pipe, loud. Lost a bit of top end and hill-climb from the B&S stinger. OK, figured that.

This is where I got curious. Instead of making a longer pipe stinger, I stuck a torquer-up pipe on the end of banana, and did my street run. After re-jetting UP, i ran another test. It ripped up my hill, top speed at least 2mph over what I had with a stinger! Instead of 2nd gear, and gear down to 1st to top my hill, it went up 3rd gear, only dropped to mid-rpm by the top.
AND...its quiet too! OMG.

I took it out for a 15 mile run, then another with my stereo!
No heat issues BTW seems about the same. That pipe by itself with another 12" made it run hot. But on the end of a banana pipe, it doesn't.

Methinks it cushions the shock wave, improves resonance of main pipe. Yet low rpm also improved. Maybe the smaller chamber has a resonance too? Not sure how that would work.


Not that it matters.
Fixed it, leaving it.
I can't explain the science of what dual expansion chambers with a stinger on a long pipe does, but my butt dyno says it makes this 48cc kick ass, yet sound like a scooter, revs fast, shifts faster, not any hotter, what's not to like?

Cleaned 'er up a bit, better sleeving and loop anchors, got rid of some zip ties.

Only thing this bike needs is a new seat, that one is shot. Almost 500 on the odo, plus several hundred as an FD drive prior.
Told my wife its a wear item, not an upgrade subject to budget veto 🤣
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DAMIEN1307

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Only thing this bike needs is a new seat, that one is shot. Almost 500 on the odo, plus several hundred as an FD drive prior.
Told my wife its a wear item, not an upgrade subject to budget veto 🤣
Your seat is one of the noseless Schwinn seats that had a fabric covering that was situated in the butt area...They no longer make it that way and use that faux leather all over the seat now and it holds up very well...I have had mine for many years, one of the most comfortable seats for a bike ever...lol.
 

Urban Fatbiker

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Your seat is one of the noseless Schwinn seats that had a fabric covering that was situated in the butt area...They no longer make it that way and use that faux leather all over the seat now and it holds up very well...I have had mine for many years, one of the most comfortable seats for a bike ever...lol.
You confirm what pictures were showing. I wasn't getting another one till I knew.
My fatbike noseless seat has springs. But I'd like to stay Schwinn, since it is what the bike says it is. 🤔
 

ImpulseRocket89

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I am no expert in the art of resonance tuning either so take this with a grain of salt. If I had to guess the second pipe you added - giving you a really long stinger with a second expansion chamber has somehow created enough resistance in the system to help with the low rpm power but also helped filter out some secondary resonance wave that helps scavenge flow from the primary chamber at higher frequencies. In any case you have me tempted to try the same thing with my 110cc engine that I am trying to tune for more low and mid range power as I already have the same clone pipe with the long head pipe waiting for it.
 

Urban Fatbiker

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I am no expert in the art of resonance tuning either so take this with a grain of salt. If I had to guess the second pipe you added - giving you a really long stinger with a second expansion chamber has somehow created enough resistance in the system to help with the low rpm power but also helped filter out some secondary resonance wave that helps scavenge flow from the primary chamber at higher frequencies. In any case you have me tempted to try the same thing with my 110cc engine that I am trying to tune for more low and mid range power as I already have the same clone pipe with the long head pipe waiting for it.
Kinda what I was thinking. It seems to act like a cushioned resistance. I actually ran two runs with my muffler stinger as my original.

Open banana maybe same top end, but lost a lot of low grunt, needed 1st to get out of my drive.
The long pipe secondary expansion w/ stinger gained over my original, higher RPM, 2mph faster, and climbed out of my drive in 3rd, a gear higher.
Plus, its much quieter, and behind me. I hear my intake loud now.

Ran it at least 20 miles today, after I did the dumbass. I ran out of gas 5 miles out. Had to pedal home. Rested, gassed up, headed back out.
(25 miles of fun m/b, and 5 miles of holy f*** am I stupid...)

Had to dammit, had a goal to make.
I hit 500 miles today woohoo!
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2speedboi

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Your seat is one of the noseless Schwinn seats that had a fabric covering that was situated in the butt area...They no longer make it that way and use that faux leather all over the seat now and it holds up very well...I have had mine for many years, one of the most comfortable seats for a bike ever...lol.

Seat posts with the shock build in adds another level of comfort. I switched bikes and the one I had switched too came with it and I was Impressed.. and now, a very happy butt too!
 

Greg58

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I’ve found that adding back pressure to a expansion chamber helps overall performance, I think it corrects some of the exhaust port timing by preventing the fuel charge from exiting the cylinder. I’ve only done 3 bikes with chamber’s but all three improved with a silencer with a smaller stinger.
 

Greg58

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Here’s the last one on a 48cc grubee.
 

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Chainlube

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Here’s the last one on a 48cc grubee.
You only need a 5/8" ID stinger from the baffle cone, yours looks like a 1" od. I totally understand not wanting to frankinstein a new pipe though.
 
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