Muffler Mod?

[CTYank]

If it improves performance, why don't they just manufacture them that way? Are the mfrs deliberately de-tuning them?

quick answer yes.....Epa reg's....But you fire up an 880 and it seems to be breathing quite well! lol

2-strokes are very visible targets to EPA, CARB etc., because of their innate propensity to spew unburnt fuel out the exhaust. Leading to current catalytic converters and stratified scavenging. It boils down to two facts:
1) Exhaust is propelled through opening port by gas pressure, with high velocity and were there nothing in its way, would happily draw mixture coming from transfers along with it. Typically there is waste of fuel (about 33%) and lots of HC in exhaust.
2) Positive pressure reflected wave can cause some of this mixture to return to the cyl. This is how expansion-chambers work; they're BIG.

With the short length of most mufflers, there's a problem enabling the return pulse, so some limiting of freedom of exhaust can reduce these emissions.

With stratified-scavenging/charge, the "mixture" that's drawn out the exhaust is air, not fuel & air. Much cleaner exhaust, reduced emissions, reduced deafness.

A lot of this muffler-modding reminds me of kids back in the day with their glasspack mufflers; noise IS power.

It's not a bureaucratic exercise. Some mfgs have been unable to comply, and closed shop. 2-stroke road bikes are gone for some time now, too.

 

[smokinj]

If it improves performance, why don't they just manufacture them that way? Are the mfrs deliberately de-tuning them?

quick answer yes.....Epa reg's....But you fire up an 880 and it seems to be breathing quite well! lol

2-strokes are very visible targets to EPA, CARB etc., because of their innate propensity to spew unburnt fuel out the exhaust. Leading to current catalytic converters and stratified scavenging. It boils down to two facts:
1) Exhaust is propelled through opening port by gas pressure, with high velocity and were there nothing in its way, would happily draw mixture coming from transfers along with it. Typically there is waste of fuel (about 33%) and lots of HC in exhaust.
2) Positive pressure reflected wave can cause some of this mixture to return to the cyl. This is how expansion-chambers work; they're BIG.

With the short length of most mufflers, there's a problem enabling the return pulse, so some limiting of freedom of exhaust can reduce these emissions.

With stratified-scavenging/charge, the "mixture" that's drawn out the exhaust is air, not fuel & air. Much cleaner exhaust, reduced emissions, reduced deafness.

A lot of this muffler-modding reminds me of kids back in the day with their glasspack mufflers; noise IS power.

It's not a bureaucratic exercise. Some mfgs have been unable to comply, and closed shop. 2-stroke road bikes are gone for some time now, too.

Some model where just choke down to pass epa with nothing else done to it so those are the one that really shine. Not enough 880's sold so there not all over that model like the 361,362,441,391. And A lot more.

 

[Kenster]

I have an MS390 that I bought new with a muffler mod. I run a 16 inch bar on it because that takes care of all my needs. This saw, with that short bar, rips through all my wood. I only cut hickory and oak. It's loud. I use ear plugs most of the time.

 

[Mcbride]

I wish people would not mod exhaust systems for more noise.
Regardless if its a car, bike, or chainsaw, they should be made even quieter if anything, not louder.

 

[smokinj]

I wish people would not mod exhaust systems for more noise.
Regardless if its a car, bike, or chainsaw, they should be made even quieter if anything, not louder.

yea I bet that 390xp just prrrr's like a little kitten! lol my 880 sounds just like an old yz 125.

 

[TreePointer]

I agreee--modding for the sake of more noise moronic.

However, the Stihl 290/310/390 series respond well to a muff mod.

 

[southbound]

My 046 with the dp cover runs stronger... Most saws will gain from a mm....