Show off your muffler mods

[Dieselshawn]

My apologies, looking back at my dyno files, we did in fact try a stock 661 on the machine with the muffler cover removed and also tried the air filter and no air filter.

The results were, there was no power difference with either.

The muffler did have the stock baffle still in there.

The baffle likely restricted exhaust power pulse flow too.

I don’t have a cover that’s in good condition to try yet.

My buddies are getting me more covers and back pieces to play with for best tuned muffler

 

[Nutball]

Today I got a decibel meter. Figured I take readings for different sound levels for different muffler mods while it runs the dyno.

An extremely loud muffler defeats the purpose of having a muffler in the first place and possibly not getting any work in town due to possible noise complaints.

Also a restrictive muffler holds back too much of the saw’s potential for making good torque and power for some models. Especially the 661’s so far. 660’s will be tested later.

The 661’s respond very well to muffler mods, including moving the power band more towards 10,000 rpms instead of 9,000.

Today I had some loggers (the owners of this 661) come to my place to see the saw run the machine.

Both of them had their ears covered with their fingers. Both said that this muffler setup is very loud.....

View attachment 307742

Picture below is the 661 at idle with the above muffler.

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This is wide open. The 661 has flatlined the gauge.

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Below is me testing my powerful stereo system.
It maxed out at 111 dba but this got complaints coming in from neighbours, not from the saws.

My stereo shakes their house. My garage was all sealed up, but the neighbours still complain about the stereo.

View attachment 307745

I am a profound deaf person that wears a powerful hearing aid but the saw above at 130 dba is painful to the open ears.

I’m deaf in both ears but wear only one hearing aid. The hearing aid easily acts as a ear plug and limits the sounds going in.

Just a short spurt at wide open is enough to cause pain in the other ear. So even I must wear earmuffs.

Keep in mind it will sound louder inside the shop because of all the hard sound reflecting surfaces. Muffler mods are not much of a bother to my sensitive hearing with good hearing protection until I cut on a big log on the ground, then all that sound reflecting back gets to be too much. It's the same running a saw next to the house and cars on the driveway vs out in the yard.

 

[Ronie]

Finished up and painted my 361 muffler a few minutes ago and ended up putting a deflector on the starter side.

 

[Mycamaro_68]

I picked up this Husqy 272 stump grinder and this is the muffler that was on it.

 

[Dieselshawn]

I picked up this Husqy 272 stump grinder and this is the muffler that was on it. View attachment 307879 View attachment 307880

Removing that Briggs Stratton 3 hp muffler and putting a proper flowing husky unit on shall yield much better power and torque.

That will make your current saw feel like it’s modified while still being stock.

 

[Dieselshawn]

I tried a mastermind 661 with no baffles or cover on dyno.

My decibel meter couldn’t read past 133 dba but idling was 119 dba.

The saw made a little less power than the triple port muffler.

I also tried a large hole and deflector over the front cover. This made slightly less power than triple port but more noise. 117 dba at idle vs 113 for the triple port.



So far the triple port is the winner.

 

[MustangMike]

I have heard from folks who know more than me ... don't vent the front cover, vent the sides as close to the saw as possible!

 

[RI Chevy]

I think the theory behind it is to change the flow. Makes it a bit quieter. With traditional carb it allows for a better idle tune.

 

[Dieselshawn]

All two strokes, (unless it’s the old Homelite EZ6 that is open exhaust) do require a certain amount of back pressure to control the air/fuel mix coming into the chamber.

An open exhaust allows the power pulse to shoot out freely and fast, causing too much suction behind which brings some of the mix out with it. Hence, loss of power.

A cover provides a certain amount of back pressure to control the pulse coming straight out.

The energy build up in the muffler chamber holds the mix back a bit just long enough for the piston to close before the exhaust goes out the exit port or multiple ports.

Tuned pipes flow very well, but by using tuned sound waves to generate back pressure to shove the fuel air mix back into the cylinder.

 

[huskihl]

 

[Woodslasher]

All two strokes, (unless it’s the old Homelite EZ6 that is open exhaust) do require a certain amount of back pressure to control the air/fuel mix coming into the chamber.

An open exhaust allows the power pulse to shoot out freely and fast, causing too much suction behind which brings some of the mix out with it. Hence, loss of power.

A cover provides a certain amount of back pressure to control the pulse coming straight out.

The energy build up in the muffler chamber holds the mix back a bit just long enough for the piston to close before the exhaust goes out the exit port or multiple ports.

Tuned pipes flow very well, but by using tuned sound waves to generate back pressure to shove the fuel air mix back into the cylinder.

Is that why Stihl's dp covers have the little sideways front exit? To help build up pressure?

 

[Dieselshawn]

Is that why Stihl's dp covers have the little sideways front exit? To help build up pressure?

It’s more likely to keep fumes away from the tree. I do have a dual port cover on the bench for a 660. Any kind of sharp 90° (example) bend in flow is restriction as well.

It’ll be more the hole size that dictates how much pressure is in the muffler.

I’m guessing it’s Stihl’s way of getting people to pay extra for better performance by buying a separate cover rather than build another style of back piece with multiple holes.



The picture above has three empty Bud Light cans on the stove.

When the triple port muffler was on the saw, those cans never moved. The factory side exhaust location above the clutch cover is one inch square. It didn’t flow much exhaust pressure to do anything.

When I put that cover with a single large hole (approx 1.250 or 1.5 inch square in size) with the big downward deflector on, the side exhaust opening had enough flow pressure coming out to blow the cans onto the floor.



So there is definitely pressure in the muffler.

 

[farminkarman]

View attachment 307987

Looks like how it should have left the factory.

 

[RI Chevy]

Nice Shawn. Good explanation. Nothing ventured, nothing gained. The old adage has some truth to it.

 

[Dieselshawn]

I can piss a higher volume of liquid than this little hole can flow. Pathetic.



This internal EPA enforced baffle is the reason the 660 is struggling to fart.



I uncorked that Epa plug and threw it in the garbage.

Took some effort to get it out.



Now for the real performance boost.... the upgraded fart box opening.



Looks purty.



I have dual port cover as well but I’m going to keep the covers closed for best performance.

I need a new flywheel key before I can run it on the dyno. That will be coming up next.

 

[MustangMike]

My experience with 660s ... for whatever it is worth ...

Ported cylinders do best with the muffler mods you did.

Some non ported cylinders have more torque with some of the baffle left in. Drilling a 1/2" hole in the back of the baffle seems to work well on some saws.

Timing may also play a big role. With ported cylinders, I like to take .030 off the key.

 

[Dieselshawn]

My experience with 660s ... for whatever it is worth ...

Ported cylinders do best with the muffler mods you did.

Some non ported cylinders have more torque with some of the baffle left in. Drilling a 1/2" hole in the back of the baffle seems to work well on some saws.

Timing may also play a big role. With ported cylinders, I like to take .030 off the key.

MustangMike:

Thank you for your information, I have a few more mufflers with baffles that I can play with.

This 660 is not ported. (Maybe for now)

I shall try the 1/2 hole in the baffle.

The larger exhaust exit is similar to the Mastermind 660 I have which also has no baffle as well. That saw is a powerhouse. I love it.

 

[Dieselshawn]

I recently tried a mastermind open side port with a closed front cover on the dyno.



It made the same power at above 11,000 and below 8,000 rpms as the triple port cover.

But between 8,000-11,000 where it matters most the machine shows the single enlarged side port is still not enough flow to let the 661 breathe.

Ive also tried the back piece the logger tried opening himself with drill bits and some sort of cutter.



This was better than a completely enclosed baffle.

Dyno showed that any kind of baffle in the muffler still hinders the exhaust flow coming out the port.

This is a good example that a saw still needs a tuned muffler for best performance.

As of right now, the triple port with no internal baffle below for either stock or modded 661 is still the power winner.



Before anyone jumps at the chance of putting a side opening on the flywheel side behind the cover, this saw is a damaged saw from a tree, so it has no chain brake handle that normally would be in the way.

This cover is tree damaged but it’s far enough forward to actually avoid the chain brake handle.

 

[RI Chevy]

How about the idle? I have found that sawz with open fronts do better WOT, but tough to idle. I experimented by trying a solid front cover. Saw idled better and had better operating mannerisms, than the open front. Just my observations.

 

[Dieselshawn]

RI Chevy: seems to be the consensus among us that we should leave the front cover alone and work around behind the cover.

The back piece.

I am finding the front cover holes to be too loud even for a deaf guy like me and has less power.

The 661 needs more flow for best performance.

I’m attempting to do work on a stock 660 but had no luck getting the saw to run long enough on the machine before shearing another flywheel key.

I need a flywheel reamer to clean up the taper