Running straight pipe on my bike now  By  Tripper (Read 2,155 times)

Tripper,

You probably need a LITTLE bit of back-pressure to get it to run just right. The stock header may be enough. If not, a longer extension might do it. I just replaced my own rotted 5-year-old exhaust on my 150 with a 1-inch inside-diameter header I made up, and a bone-yard expansion/contraction chamber "muffler" made for a 50cc. It's as "straight-through" as it gets, with NO baffles of any kind. Amazingly, it's SUPER-QUIET.



My guess is that the large expansion-chamber bleeds off all the velocity of the exhaust gases, then this low-pressure gas goes through the "U-turn" pipe and into the teensy straight-through glass-pack mini-muffler.

At any rate, it tunes easily, runs strong like a good straight-pipe and is very quiet... With these scooters (considering their sometimes "marginal" engineering) it pays to experiment!

Nothing beats a well-tuned straight-pipe setup, but my neighbors seem to like mine... LOL... and it still runs like a bear!

Leo (exhausted... LOL!) in Texas

Well, it performs better but still vrapp. I think it may need a bigger carb. I'm gona go up a jet first, but idk if that will slove the problem.

I think this question was about my pictured exhaust...? If so, it runs GREAT! I think the expansion/contraction chamber with the little "muffler" was made for a 4-stroke 50cc GY6. It has no manufacturer I.D. or any identification on it, but the header-pipe with mounting flange which I removed is identical with other 50cc GY6 pipes I've seen. These (as well as similar setups) are often seen on 4-stroke engines with good results. The Vento "Phantom" has such a setup from the factory, though it's HEAVY chrome-plated steel (I have one sitting in my shed, and it's a beautiful "boat-anchor") while this one is feather-light stainless and aluminum. The light weight is why I used it, instead of the prettier chrome Vento unit.

As for noise, it is INCREDIBLY quiet. At idle, it sounds like a stock muffler, but quieter. Sounds like a small air-compressor. At WOT it has just a little "bark" but not at all loud.

No problem running a straight-pipe in Texas... Dealers sell both new and custom hogs with straight-pipes and megaphones... LOL! And they pass state inspection with no questions. Talk about LOUD!!! We're talking window-breaking, eardrum-busting hellfire-loud... HeHeHe.

I can't explain just WHY this wide-open exhaust is SO quiet, except that the HUGE expansion-chamber must allow the exhaust to deplete in velocity before exiting the little straight-through glass-pack as a mere whisper.

That big chamber also creates a low-pressure area, scavenging the exhaust which is why these work well on 4-strokes. Definitely NOT as well as they do on 2-strokes, where they actually pull more air-fuel mix in and ram it back, creating a supercharging effect... But still better than a traditional 4-stroke pipe and muffler.

I'm NO aspiration expert, BUT I learned these little gems of knowledge WAY back in my racing go-kart days in the early 1960's. Expansion/contraction chamber technology was brand-new then. A properly designed setup would give us a 50% power increase on our McCulloch and West Bend kart motors... We're talking 35+hp at 20,000 rpm from a 10 C.I.D. 2-stroke!!! That's a similar size motor to our 150's that are doing great to put out 10hp.

Once we figured out what made the systems tick, we tried them on 4-stroke engines and saw MODEST increases in power from the improved scavenging.

I was already running a richer main jet with the UNI filter and stock muffler, and I will definitely keep an eye on the plug. After putting some miles on the clock, I'll post a test of overall performance. That will take a little time, I'm still wrenching on it.

Only extended riding will tell if this a good setup, but right now, after some short runs, I'm betting it's a winner... Quiet as a mouse, and runs like a bear... LOL!

I realize this reply isn't very technical, but I'm no mechanical wizard, just an aging old "trial-and-error" wrench-turning dinosaur, lost in the sixties... and it's the best I can do...

Sincerely,

Leo in Texas

yeah, put a horn/trumpet as your exhaust pipe!