660 Muffler

[sun64]

I purchased a US 660 in Australia. I ditched the US muffler and put on a dual port. What a waste of time they are. No wonder the saws hardly go.
I used a 1/4 carbide bit in a drill and opened up the small holes in the internal cage.
I ground 4 of the small holes into a 5/8 x 3/4 hole. I did this on all 3 sides of the cage where the small holes were.
I then drilled a 5/16 hole in the upper end of the front baffles plate.
I opened up the side hole on the dual port as well and replaced the tiny mesh with 2mm stainless steel screen I have here.
I also matched the muffler to the gasket.
I left the front baffle plate in place , except for the small hole I drilled in it to help put a bit of backpressure back into the cylinder.
The rest is preety gutted though.
My guestimate is with the larger mesh, I am at around 95 % of port opening. 85 to 100 % is all you need .
I have never started a fire with my larger mesh. I only put it in to keep the wasps out from making nests in there.
Hope this helps, but those stock mufflers are way too restrictive for the saw.
I also changed out the main jet in the carb , from a 62 to a 74.
A lot more power now.
Wayne

 

[Anthony_Va.]

I got a really good gain out of my 660 with the muffler mod I did. No welding nessesary.

I opened up the stock outlet to around 7/8" from the outside with a dremel. If youre careful you can do a good job without hacking it up. Just raise the deflector with a screwdriver, then bend it back down straight when you're done.
After that, cut the front off the baffle. I think that is the best thing you can do for a 660 muffler. The baffle hurts the power IMO.
Then I installed a DP cover. I did'nt do any modification to the DP outlet.

My 660 gained a ton of throttle response and a few hundred RPM in the cut. It made a difference that I could feel. Also had a good, deep sound and sounded really good without being too loud.

 

[closetoreality]

I got a really good gain out of my 660 with the muffler mod I did. No welding nessesary.

I opened up the stock outlet to around 7/8" from the outside with a dremel. If youre careful you can do a good job without hacking it up. Just raise the deflector with a screwdriver, then bend it back down straight when you're done.
After that, cut the front off the baffle. I think that is the best thing you can do for a 660 muffler. The baffle hurts the power IMO.
Then I installed a DP cover. I did'nt do any modification to the DP outlet.

My 660 gained a ton of throttle response and a few hundred RPM in the cut. It made a difference that I could feel. Also had a good, deep sound and sounded really good without being too loud.

Pry it? Isn't the external deflector tac welded?

 

[Mastermind]

 

[Stihlman441]

Open up originall port,remove some or all of the internal baffle,add extra port and defletor.

 

[sun64]

Nice pis but that is a 460- dual port muffler

 

[Mastermind]

Nice pis but that is a 460- dual port muffler

MS461 actually, but the idea is the show how to remove the baffle without all the grinding these guys were talking about.

 

[blsnelling]

Send me your muffler body. I'll open it up for you. You can get all the opening you need under the factory deflector. You're spark arrestor will still be functional, and you won't have to spend money on the DP cover. This ones on me.

 

[cutforfun]

Send me your muffler body. I'll open it up for you. You can get all the opening you need under the factory deflector. You're spark arrestor will still be functional, and you won't have to spend money on the DP cover. This ones on me.

Taking work away from wojo he is not going to be happy, good for you on the freebie

 

[blsnelling]

Taking work away from wojo he is not going to be happy, good for you on the freebie

Oh no! Now I've gone and offended someone else, lol

 

[sun64]

MS461 actually, but the idea is the show how to remove the baffle without all the grinding these guys were talking about.

I have always thought that a little bit of backpressure / pulse to keep the new incoming charge in was benificial to stop unburnt fuel leaving the exhaust, esp on 2 strokes
Only slight backpressure
On some motors, with a propper designed exhaust they perform better and are cheaper to run.
That is not always the case with chainsaws, they have a tiny exhaust system, not like a bikes where the powerband really comes in with the exhaust pulsing back at certain revs
Depends if you want a screamer or something you can afford to run etc
Interesting, I am all ears if there is any information on serious mods with real gains and not using a fuel truck behind you
Best regards Wayne

 

[Mastermind]

I have always thought that a little bit of backpressure / pulse to keep the new incoming charge in was benificial to stop unburnt fuel leaving the exhaust, esp on 2 strokes
Only slight backpressure
On some motors, with a propper designed exhaust they perform better and are cheaper to run.
That is not always the case with chainsaws, they have a tiny exhaust system, not like a bikes where the powerband really comes in with the exhaust pulsing back at certain revs
Depends if you want a screamer or something you can afford to run etc
Interesting, I am all ears if there is any information on serious mods with real gains and not using a fuel truck behind you
Best regards Wayne

I've tried about everything from a tiny outlet to a tuned pipe.....even did some with no muffler. Remember that many of the older saws just had exhaust stacks......

I have come to believe that the slight back pressure of a canned muffler that has a 80-85% outlet to exhaust port ratio seems to work well on a work saw. If you expect fuel economy out of a MS460 or a 660 though....well that ain't gonna happen.

Perhaps a Husky strato saw is what you want.

 

[sun64]

Thanks for the advise and knowledge Randy.
I know a 660 likes its fuel.
Iwas just querious if some mods work better than others without sacrificing any more fuel than is necessary