Final word on baffles...necessary or not?

Discussion in 'General Questions' started by spunout, Sep 17, 2007.

  1. spunout

    spunout Member

    After a mind-numbing hour of reading the archives, I get conflicting results. Some posts (many months ago) say back-pressure is needed. a more recent post claims 'these little engines don't need back-pressure.'

    So, now that everyone's more experienced and (hopefully:p) knowledgeable...can we get the final word on this issue?

    If the majority says baffles are needed, what is the potential damage/symptoms of running without?
    I've noticed some custom pipes do not have them.
     
    Last edited: Sep 17, 2007

  2. rcjunkie

    rcjunkie Guest

    backpressure helps a little bit with low end torque but no backpressure allows for greater power at higher revs. Removing baffles may require rejetting the carb or adjusting needle clip height to ensure mixture is not too lean.
     
  3. Dan Hunter

    Dan Hunter Guest

    I have a limited understanding of the process and likely someone else with a better one will chime in but here's my understanding of the issue:

    If you're running a two-stroke, sonic reverberation plays a major part in keeping the fuel/air charge dense as the piston finishes rising above the exhaust port. It discourages flow at the port while the enertia of the air coming in the intake "supercharges" the cylinder above atmospheric pressure thus maximizing density and enhancing performance. The elaborate contouring (conical shapes of expansion chambers) and length of exhaust pipes focus that sonic wave for intensity and timing to maximize the effect with variances to assist port timing in contouring the power band.

    After the point of sonic reversion, anything restrictive just impairs the engine's ability to respire...mufflers, whatever. Baffles are just a simpler, less expensive and less efficient way to manage sonic reversion. I'd leave it alone.
     
    Last edited by a moderator: Sep 18, 2007
  4. rcjunkie

    rcjunkie Guest

    If I am wrong please correct me. Dan, that sonic reverberation is the specific process by which a tuned pipe works. Our engines do not have an expansion chamber/tuned pipe exhaust so don't think you get much of a "tuned effect".
     
  5. Dan Hunter

    Dan Hunter Guest

    Nope, not much but still some...the finger in the dyke of tuning. And please forgive me for the mistype - its reversion not reverberation. How embarrassing.
     
    Last edited by a moderator: Sep 21, 2007
  6. Dockspa1

    Dockspa1 Guest

    Dan, I must concur about the finger in the dyke situation. Leave it where it was. Even though these are cheap happy timers, they still have to sell and in order to keep selling they have to have a product that has been sort of super tuned, to keep customers buying.
    By the way, this is the first R rated exahust situation I have ever come accross!
    Doc
     
  7. fourfeathers

    fourfeathers Member

    Hi guys, just a little note from Newzealand. It's the stinger pipe that controls back pressure, it's acts as a pressure release valve and can be tuned for whatever aplication the engine is going to be used for. Lots of web sites concerned with this subject. No baffles on my bike and it's very effective and has been for 2000Ks with no adverse conciquencies.

    have fun!!!
     
  8. Fabian

    Fabian Well-Known Member

    My opinion is unqualified as i'm not an engineer, "but", my own empirical data suggests that the manufacturer knows more than we do about the reliability of their engines.

    My opinion: Quite simply, do not modify the muffler - that's it - do not modify the muffler.

    You will have the most amount of low and medium rev torque available and it's exactly in this rev range where you want to be motoring along, ideally with a SickBikeParts Shift Kit to keep the engine in the "low" rev range and use the extra torque to ride at similar speeds to a motor revving it's guts out and making no more effective power.

    If you keep the revs low, the lower end (big end) bearing will give long service life - this seems to be the main reliability issue.
    My engine is completely standard except for a modified intake tube (pipe) that seems to have enhanced low rev engine torque.

    I run what seems like impossibly low engine revs compared to my previous engine where the inner exhaust pipe was cut to the base.
    It was significantly noisier (irritatingly noisy) and the engine wanted to rev quite hard.
    After 700 kilometers it blew the bottom end bearing.

    With my new engine, i've travelled over 1200 kilometers and using very low revs, i'm going no slower, furthermore, the engine doesn't vibrate my bone marrow, nor other bits of my body.
    It's quite relaxing to ride without a noisy racket bashing your eardrums and vibration rattling your teeth.

    Fabian
     
  9. motorpsycho

    motorpsycho Active Member

    it's a proven fact that any motor hat has a free flowing exhaust and intake will make more power than one that has a restrictive exhaust and intake. the stock pipe and muffler is VERY restrictive on these little motors.
    an expansion chamber and hi-flow air filter will free up some extra power.
    this whole engine was made to be modified.....leaving it stock just isn't good enough in my opinion.
    the engines are cheap enough that you can just replace it if you mess something up.
    as far as i know, the only way to "blow" a 2 stroke is to run it lean....they can be bulletproof and they can run for a VERY long time.
     
  10. fourfeathers

    fourfeathers Member

    Modifying H.T. motors

    I'm on board with you Motorpsycho on this one. My 70cc is heavily modified and goes like a rocket and is relyable to. I regularly do 300kmer runs and have clocked up almost 3000kms to date. The motor has been striped down and the internals look excelent. Because of the mods I run 25-1 oil mix. I agree these engines lend themselves to heaps of mods. Years ago I was involved with drag racing so I guess I'm up with the tricks required. The only mod I have'nt done yet is a jack-shaft shifter kit which I'm just about to start on, need to work out what gears I'll need for the rear casset and I reckon I can get this little sucker to kick 80-100kmph. Drop me a line on your mods I'd like to swap some ideas.


    Old petrol-heads never die they just loose their cubic-centimetres :devilish:
     
  11. motorpsycho

    motorpsycho Active Member

    i too was a drag racer in the 80's and i have done a ton of engine work / mods. in my life. as for what i have done to my littel 50 c.c.:
    so far, i've added an expansion chamber with no baffle / muffler/ silencer, a high flow air filter, and a boost bottle.
    over the winter i plan on porting & polishing the intake and exhaust, and milling the head.
    My motor is on a 20" frame and i do not / can not install a shift kit / jackshaft kit...so i have to get the most that i can out of a single speed.
    As of right now, my bike has topped out at 38 mph, and i weigh 155 lbs.
    I liike more for short bursts of high speed rather than constant crusing speeds.
    the plan next summer is to take it and run it on an 1/8 mile drag strip against my friends 24" bike with an 80 c.c. motor on it.
     
  12. oldsalt

    oldsalt New Member

    My experiance with my RAW '80cc' motor is that it was so rich that something had to be done. I was going to solder up the main jet and redrill but decided to look at the inerds of the big sausage muffler [obviously a muffler, not a tuned pipe]. I was astounded by a reverse flow pipe and all manner of baffles in there! All I could figure was that the enginner's mother was scared by a loud moped before he was born. So, in an effort to lean out the top end I removed about half the junk. That leaned out the upper end enough so that it did not run constantly in a 4-stroke mode. Took the pipe off again and performed a complete baffle removal. Now the engine will run most of the time in a 2-stroke mode. At wide open throttle it reverts to the over-rich condition and starts 4-stroking, I can live with that.

    Now to the point of all this: If you are already lean on the mid and/or upper end leave it alone. Do some carb work, then consider gutting the muffler. It your bike runs fine then be prepared to richen up the carb if you gut the muffler. By the way, the noise increse, with the gutted muffler, was not enough to write home about.
     
  13. fourfeathers

    fourfeathers Member

    Hi Motorpsycho,
    nice to hear of your shared interest in drag-racing, heaps of fun ah!.
    Have spent all day tuning and re-configuring a velocity stack for my modified carby.
    Heres a little tip I've never seen mentioned anywhere on the forum.
    When you take the jug off you'll notice that the bottom of the cylinder sleeve protrudes and partially covers the intake end of the transfere ports. By cutting and grinding this restriction/ configuring to the shape of the transfere port increases fuel flow no end with a marked improvement to performance. Make sure inside edges are re-beveled or you'll have trouble getting the rings into the cylinder again.

    Catch yer later. Have fun.
     
  14. Frogz

    Frogz New Member

    i was riding 1 day, for some reason my bike was being kinda loud
    evedently the bolt fell out of my muffler and the end was hanging out(amazingly, i didnt lose it)
    bought a new bolt(hex head) to replace it with, the bike ran fine without "any" backpressure, the end was fully off however
     
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