ported 661 baffle in muffler vs baffle out

[Moparmyway]

I will need in ear plugs and ear muffs. LOL
I've done that before. I hear crackles, but no popping.

I had asked a question earlier if a saw would run better with 1 big exhaust port or 2. The 1 big port may help prevent the "venturi effect. "

Venturi effect is Docs "posted hypothesis" (he could be fishing for comments)

I think its just lack of backpressure allowing enough oxygen to combust the unburned extra rich fuel


Those "crackles" could be exactly what we're looking for

 

[RI Chevy]

Hmmm. Interesting stuff. Does the popping hurt the saw in any way? Or is it all external combustion?

 

[RI Chevy]

Maybe you could post a video of this popping? So we can get a better understanding of what is being conveyed here? Please. Lol

 

[huskyboy]

Wasn’t the reason jms’s 661 was popping the way he hacked the lowers into the wall to be like a 395 cylinder? That was discovered by people who tried to fix his saws was it not? I remember reading it somewhere way back when *s-word hit the fan.

 

[MustangMike]

I think Keven is identifying the problem, but based on my past experience I will offer a possible different reason.

I believe the lack of back pressure in the muffler is just allowing too much unburned fuel into the muffler and the heat is igniting it.

My "guess" is based in part of the saw that I opened up the muffler "too much" on, and it sucked fuel like crazy. Obviously it was spitting out unburnt fuel.

A little back pressure may make the saw run more efficiently.

 

[huskyboy]

I think Keven is identifying the problem, but based on my past experience I will offer a possible different reason.

I believe the lack of back pressure in the muffler is just allowing too much unburned fuel into the muffler and the heat is igniting it.

My "guess" is based in part of the saw that I opened up the muffler "too much" on, and it sucked fuel like crazy. Obviously it was spitting out unburnt fuel.

A little back pressure may make the saw run more efficiently.

I see what your trying to say... I think. So in theory less BD wants a more open muffler and more BD wants a more restricted muffler to work well? This is where I start to get lost. Lol

 

[RI Chevy]

I just tune my saws so pig rich that the oil prevents the fuel from burning. The end result is shiny well oiled piston and jug. I presume the bearings are also well lubed too...[emoji16]

 

[Moparmyway]

I think Keven is identifying the problem, but based on my past experience I will offer a possible different reason.
I believe the lack of back pressure in the muffler is just allowing too much unburned fuel into the muffler and the heat is igniting it.
A little back pressure may make the saw run more efficiently.

Nice post Mike !

Efficiently means different things to different people.
Make no mistake, these saws are gunning for max power, not max fuel economy.
I can cut more efficiently, so I can have a XXX before you, because I finished cutting.
Yes, I'm probably going through more fuel, but I'll take that trade for my saws.

IF I port a saw for someone, I allways ask them what their expectations are and port the cylinder and muffler accordingly.

Maybe you could post a video of this popping? So we can get a better understanding of what is being conveyed here? Please. Lol

I tried videoing it and the sound is just fuzzy. Mayhaps the dual sewer pipes and extreme openings made the saw a just a little louder ?

Maybe I can try from different locations so the microphone doesnt wig out ..................

 

[RI Chevy]

It must be like a Big V8 with muffler Drone. Lol

 

[huskyboy]

Nice post Mike !

Efficiently means different things to different people.
Make no mistake, these saws are gunning for max power, not max fuel economy.
I can cut more efficiently, so I can have a XXX before you, because I finished cutting.
Yes, I'm probably going through more fuel, but I'll take that trade for my saws.

Your right, efficiency means different things to different people. When you are logging like I am, a real bad fuel hog isn’t so ideal. While a guy is still fueling up a thirstier saw I am still cutting wacking and stacking timber feeding the forwarder/skidder/felling machine operator who is constantly right behind you all day long. With a efficient saw, I can get ahead of them and take more breaks. If I was cutting firewood or a tree service guy it wouldn’t matter much at all. It still adds up over time though. I do understand the gain in power is often worth the fuel used most of the time... but there is a tipping point where it becomes annoying and it’s not a worksaw anymore.

 

[MustangMike]

I see the points both of you are making, but I don't think your guys are totally in line with what I was trying to say.

I expect a ported saw to burn fuel faster, but I also expect it to cut faster, and may even be more efficient.

But I was not really going there.

Unburned fuel escaping into the muffler is not producing more power. If that is happening, a slightly more restrictive muffler may provide THE SAME POWER w/o the popping, and likely better fuel efficiency.

The muffler should be matched to the saw (including porting, etc), but we don't have any super duper computer program to tell us exactly how to do that, so we are left to experimenting.

I'm not advocating closing up the muffler to exchange power for fuel economy, I'm just stating if the muffler is "too open" for a particular saw, you may be able to close it some and retain the same power and gain some fuel efficiency.

I'm not saying this WILL happen, I'm just saying it is a POSSIBILITY.

 

[Pincher]

The compression comes from the exhaust.....everybody knows that....

 

[Pincher]

I know we are not dealing with anything that resembles a piped saw but unbernt air/fuel mixture does escape into the exhaust and is forced back at a predetermined rpm. Pipes are above my pay grade.

 

[MustangMike]

I have heard of back feeding transfers, but not the whole length of the exhaust port! I agree with your fist statement (that some escapes), but not that it returns.

I guess the questions boils down to "Is the amount escaping excessive and counter productive?"

 

[Pincher]

I have heard of back feeding transfers, but not the whole length of the exhaust port! I agree with your fist statement (that some escapes), but not that it returns.

I guess the questions boils down to "Is the amount escaping excessive and counter productive?"

I guess I was just referring to piped two strokes and the fact that some unburnt fuel and air make it into the exhaust and it does not ignite. On a work chainsaw, returned air/fuel from the muffler is negligible.

 

[Adirondackstihl]

If the popping occurs on a cold muffler.....
Argument is invalid

 

[Moparmyway]

Unburned fuel escaping into the muffler is not producing more power. If that is happening, a slightly more restrictive muffler may provide THE SAME POWER w/o the popping, and likely better fuel efficiency.

Unburned fuel escaping from a 2 stroke is a byproduct of the way a 2 stroke works. The more air you can pump through it, (along with more fuel) the more power you can make. More power will give you more unburned fuel out the exhaust.

The wierd noises only happen at part load, and throttle settings above 1/2-3/4. The little pops are happening tank after tank

Make no mistake, all 3 saws had one opening, two smaller openings, and finally the two larger openings.

Each saw gained power in the cut and better throttle response with more exhaust opening.

If anyone has an extra 661 muffler, I’d be happy to weld up something different from what I’ve got, something that has even more open area with dual sewer pipes and test against a stock one, a slightly modified one, mine, and the dual pipe exiting from each side. The donor can pick which one of the 4 mufflers they want returned, or I’ll work out purchasing the muffler and keep them

I have a oem 346 muffler, a normal muffler mod dual port with deflectors, and the dual sewer pipes. She’s the most angry with sewer pipes.

Ive got a stock 562 muffler and had a normal muffler modded (gutted the inner tube and widened the exit to the stock deflector) muffler, which is now sporting the dual pipe exits. She too is the most angry with sewer pipes.

 

[RI Chevy]

Interesting...

 

[Deets066]

Boost ports are used as a way to push spent charge out of the cylinder. If your getting complete fill of the chamber, then; using extra fuel to push out the charge faster can result in more power and more rpm.
So, on a properly setup 2 stroke, you will always have fuel in the exhaust.
In the case of a saw, with a can muffler, the faster you can get the spent exhaust out the better. But, in an effort to completely fill the chamber there will be excess fuel. Instead of using it to push out the charge, it’s simply sucked out.
Restricting this flow will simply cause the fresh charge to mix with more of the spent charge that back feeds the trans.

 

[MustangMike]

Sounds like Keven has done the proper muffler testing (with each one producing more power in the cut) so that my concern IS NOT VALID HERE.

And DEETS and Keven are both right that a 2 cycle is not real efficient, and it will always release some unburnt fuel, and the IN GENERAL the more power you produce the more unburnt fuel will be released.

That said, the premise that excessive unburnt fuel will always produce more power is FALSE, and I believe TM has commented on it in the past.

A 2 cycle engine is not just a constant flow, it is a series of pulses (all engines are), and when your components are in sync it will run better. There are situations when some additional back pressure will produce more power.

There are times when excess unburnt fuel being drawn into the muffler will cost you power. Fuel remaining in the combustion chamber will produce more power than unburnt fuel in the muffler.

Even a tuned pipe has a very large expansion chamber and a small outlet. Think about why that is. To listen to Kevin and DEETS, you would think no muffler at all would out perform a tuned pipe, but that is not the case.