Exhaust repercussions if any



The_Aleman

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What do I mean? Didn't you read the link I posted?

Arbeitsweise_Zweitakt.gif


2-stroke exhaust is designed to push a portion of the exhaust back to keep the combustion chamber filled. Strategic backpressure.

You can cut the muffler off of that exhaust and slip some flexpipe over it to make an exhaust pipe for your 4-stroke tho. A small seatclamp to keep it in place on the header. Chinagirl exhausts make awesome headers and they do bolt up to the 49cc 4-strokes. I did that on mine.
 

Will'smotobikes19

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Actually the stock 4 stroke exhaust is quite similar to the 2 stroke the header angle is different though. Drill holes in the cap and chop that tube that sticks up in the muffler. A huasheng with a straightpipe sounds amazing though. There was a vid of someone with the phantom bikes exhaust with baffle removed but can't find it. If you don't want the flexpipe you can get someone to chop the muff and weld and bend a pipe and make brackets for it. Speaking of these exhausts I took a ride on my tle43 clone setup earlier and the exhaust in the 2nd pic (only black) nearly fell off! bolts somehow didn't fall out completely. Time to studd up and loctite.

#1 4 stroke

4 stroke exhaust.jpg



#2 2 stroke

2 stroke exhaust.jpg
 
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The_Aleman

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I've tried the 4-stroke "kit" muffler and it was even worse than the compact box muffler the engine actually comes with. The box muffler is ugly, but it actually works just fine up to 7K RPM out of the box and the engine has a decent powerband with it. The kit muffler sounds like ass and performs like it, too. Engine runs hotter with all the backpressure it has.

It's a perfect example of mass-produced kit junk that gets repurposed for an application it does not really fit. We can do the same thing, but to a proven benefit: Take a chinagirl exhaust, cut the muffler off. Attach about 30" of flexpipe, or it can be straight tubing with silicon bends. The big Briggs cigar muffler is perfect in that it keeps max flow and snarly tone but greatly reduces exhaust noise in neighborhoods.

Edit: https://motoredbikes.com/media/01-23-2012.43982/full
Sounds like:
 
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Old Busted Hotness

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They call those poo-poo mufflers for a reason.

If you're using a 2-stroke exhaust on a 4-stroke, bear in mind there are half as many exhaust pulses, so the tuning effect will be off by half. A 2-stroke exhaust meant to work at 5,000 rpm won't "come on the pipe" til you hit 10,000 on a 4-stroke. I don't think any of these little engines will do that kind of rpm more than once.
 

FNTPuck

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They call those poo-poo mufflers for a reason.

If you're using a 2-stroke exhaust on a 4-stroke, bear in mind there are half as many exhaust pulses, so the tuning effect will be off by half. A 2-stroke exhaust meant to work at 5,000 rpm won't "come on the pipe" til you hit 10,000 on a 4-stroke. I don't think any of these little engines will do that kind of rpm more than once.
A 4stroke has valves and does not rely on exhaust scavenging for power band or tuning like on a 2stroke. RPM range of a 4stroke is based mostly on the cam profile (primarily the valve overlap, duration, and LSA). Although some backpressure does move the TQ peak lower in the RPM range, its not actually making more TQ - its just making the same or less TQ earlier on.

They need as little restriction as possible - for performance that is ideally just a straight pipe to keep the valves from burning up. Low end power will be sacrificed in exchange for higher RPM power and a wider usable RPM range.
 

Will'smotobikes19

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They call those poo-poo mufflers for a reason.

til you hit 10,000 on a 4-stroke. I don't think any of these little engines will do that kind of rpm more than once.
crazydan has had his race motor up to 9,800 rpm I think he said or atleast 9k. Zenoahs and goped motors can do 11, 12k.
 

JerboaJohn

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that's it,, scrounging up some cash to get a billet rod and flywheel for the 118 n axe the governor hahaha. I need rpm too!! but I dont have ZenoahSubbieorCrazyDanbuilt4stroke that revs to the moon lol
currently it tops @ 4200,w/ governor tweaked
 
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