can a muffler be overported? is there a damage risk?

[cyborgben]

I posted this previously, but I made the mistake of having too many topics in one post, so here goes...
I bought a used logger saw with about 10 holes punched into the muffler, I realize that the H jet will need enriched over stock, but am I running any risks of damaging the saw because of too many holes?
What would happen if you took the muffler off? (other than heat and noise...) - not that I plan to, I am just trying to understand how these engines work...
In the car world running open exhaust seems an area for debate. some say no problem, others say that engines need some back pressure and the cold air going in on shutdown leads to cracked valves...

 

[old-cat]

I took the front cover off a STIHL 036 and fired it up one time. About 5 seconds is all I could take, pure PAIN!!

 

[Moparmyway]

Damage to the saw with too large or too many openings?....................................................... Probably not
Result of too large of an open area ?............................. Excess fuel consumption, erratic idle, unburned fuel spitting out of muffler
Result of no muffler ? .................................................... Possible damage to rings/piston, I believe the muffler help to keep ideal temperatures for piston/rings/cylinder to work well together

Damage to yourself ? ..................... hearing loss and BIG headache

I believe a little back pressure is a good thing, but not too much or you will loose power. I tend to go aggressive for some, but my stuff runs great

 

[blsnelling]

Won't hurt a thing if tuned for it.

 

[cyborgben]

Thanks so much. I feel safer now.I assume it was like that in the woods for years before I owned it so damage would have already occurred, but even a used saw is a big investment for me and I just wanted to be careful.
Mopar, what are all those black white and shiny pieces all over your saw? Mine are all 50 shades of brown??!! Seriouslythough, thanks for taking the time to help...much aappreciated!

 

[nmurph]

Won't hurt a thing if tuned for it.

^^^^^This^^^^

 

[Moparmyway]

Mopar, what are all those black white and shiny pieces all over your saw? Mine are all 50 shades of brown??!! Seriouslythough, thanks for taking the time to help...much aappreciated!

Those are pieces of metal from removing material from the muffler opening. I took those pics as I finished grinding on it.
have you got any pictures of that muffler with all of the holes you could post up?

 

[J.Walker]

What did you say.......
My hearing is not to good any more!

 

[spindrift7mm]

If you run screens which I recommend it take more opening area than you think. My ported Stihls run well triple ported. Those 1" pipes might look cool but with no screens no telling what ends up in the cylinder. Can't run the open exhaust out here. Ken

 

[singletrack100]

If you run screens which I recommend it take more opening area than you think. My ported Stihls run well triple ported. Those 1" pipes might look cool but with no screens no telling what ends up in the cylinder. Can't run the open exhaust out here. Ken

Yah, it may not hurt the saw if done right but out here, it might hurt your livelihood when those huge sparks/flames etc. come spewing out setting the woods on fire! Screens all the way!

Duane

 

[Chev727]

I feel you want some back pressure still, more you open it the less torque you get but may gain horsepower, and a ton of noise, that's only my opinion though

 

[riley1056]

From my experience they like huge holes when tuned for it. You just don't get the scavaging effect of a tuned pipe with these mufflers so let em flow.

 

[jughead500]

I opened up a 036 muffler the other day and done what old cat said.piss revved it and shut it down.even the echo was painful. of course i was used to it from running the pm700 half of the day.

 

[cyborgben]

Those are pieces of metal from removing material from the muffler opening. I took those pics as I finished grinding on it.
have you got any pictures of that muffler with all of the holes you could post up?

I was joking about how clean your saw looked, not the shavings. I have never owned a new saw and yours sure looked pretty...
I will put up pics later if I can get to the barn ...

 

[Moparmyway]

I was joking about how clean your saw looked, not the shavings. I have never owned a new saw and yours sure looked pretty...
I will put up pics later if I can get to the barn ...

Sorry, my sense of humor left me for a day or two, been dealing with an unruly grump ...............
I did the muffler mod to the new 661r pretty much right away, seeing how small the opening was for a 90cc engine, and knowing how my 066 woke up like it had a shot of adrenalin with that muffler mod.

She is pretty dirty now, I do clean each one at the end of the day, so it might not be grungy ............ but it is well used !!

OK, waiting on the

 

[CTYank]

2-stroke exhaust is not "pumped" like in a 4-stroke, but depends very much on pressure waves that head out on opening the exhaust port. Following the positive-pressure part of the waveform, you get a negative-pressure part of the waveform. Back when, McCulloch put warnings in owner's manuals to not remove the muffler totally. Story was that the engine could suck poo back through the port. The negative pressure time.

 

[SL Wrestling]

Yes a muffler can be over ported, two-strokes need some back pressure. In two-stroke theory, the muffler exit on a tuned exhaust system should be about 80% of the cylinder exhaust port. I have run a muffler cover with 10 3/8" holes drilled in it and a muffler cover with a 1" pipe port in it and a spark arrestor screen is recommended. Now the drilled cover was on my Stihl 046Magnum (Blown up and scraped) and the piped cover is on my Stihl 460Magnum (Almost blown up). I have not tried the drilled cover on the 460 for comparison (Maybe after installing a piston and cylinder kit).

 

[Chris-PA]

Yes a muffler can be over ported, two-strokes need some back pressure. In two-stroke theory, the muffler exit on a tuned exhaust system should be about 80% of the cylinder exhaust port. I have run a muffler cover with 10 3/8" holes drilled in it and a muffler cover with a 1" pipe port in it and a spark arrestor screen is recommended. Now the drilled cover was on my Stihl 046Magnum (Blown up and scraped) and the piped cover is on my Stihl 460Magnum (Almost blown up). I have not tried the drilled cover on the 460 for comparison (Maybe after installing a piston and cylinder kit).

Welcome to AS! The thing is that these are NOT tuned exhausts.

2-stroke exhaust is not "pumped" like in a 4-stroke, but depends very much on pressure waves that head out on opening the exhaust port. Following the positive-pressure part of the waveform, you get a negative-pressure part of the waveform.

This true. With no can or partially enclosed volume at the port exit, any of the fresh fuel charge that goes out the open exhaust port will be lost to the atmosphere, and fresh air will be pulled back into the cylinder - this is air that did not go through the carb and did not pick up fuel. That's why if you really open it up you may need to enrich the H to make up for that extra air.

With a less open can then some of that fresh fuel charge that goes out the port, probably along with some exhaust, will get pulled back in, with less fresh air. That means all the air that goes into the engine went through the carb, and if the muffler mod successfully increased flow then the mixture will have gotten richer, not leaner.

Opening the exhaust up wide should not hurt anything if you tune for it, and may be the max power approach. But it may also increase fuel loss out the port, and will be louder. And I suppose may allow stuff back in without a screen.

 

[CTYank]

Welcome to AS! The thing is that these are NOT tuned exhausts.

This true. With no can or partially enclosed volume at the port exit, any of the fresh fuel charge that goes out the open exhaust port will be lost to the atmosphere, and fresh air will be pulled back into the cylinder - this is air that did not go through the carb and did not pick up fuel. That's why if you really open it up you may need to enrich the H to make up for that extra air.

With a less open can then some of that fresh fuel charge that goes out the port, probably along with some exhaust, will get pulled back in, with less fresh air. That means all the air that goes into the engine went through the carb, and if the muffler mod successfully increased flow then the mixture will have gotten richer, not leaner.

Opening the exhaust up wide should not hurt anything if you tune for it, and may be the max power approach. But it may also increase fuel loss out the port, and will be louder. And I suppose may allow stuff back in without a screen.

The notable (to me) point of what I was trying to paraphrase from Mac manual, was the danger of sucking nasty stuff back into the chamber, with any gases. Mechanical damage there kinda renders momentary power gains irrelevant.

 

[Chris-PA]

The notable (to me) point of what I was trying to paraphrase from Mac manual, was the danger of sucking nasty stuff back into the chamber, with any gases. Mechanical damage there kinda renders momentary power gains irrelevant.

Yes, as long as there are pressure pulses you could pull in small stuff - there is a filter on the intake!