Final word on baffles...necessary or not?

spunout

Member
Joined
Apr 24, 2007
Messages
769
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.
 
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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.
 
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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.
 
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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".
 
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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.
 
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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
 

fourfeathers

Member
Joined
Jun 18, 2009
Messages
52
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!!!
 

Fabian

Well-Known Member
Joined
Sep 8, 2009
Messages
4,521
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
 

motorpsycho

Active Member
Joined
Aug 5, 2009
Messages
2,252
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.
 

fourfeathers

Member
Joined
Jun 18, 2009
Messages
52
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:
 
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