Thread: Lakeside53's --361 muffler mod w/photos

Hi! could anyone tell me how to remove the muffler from a 361? I want to do some mods to it but do not want to damage it while trying to remove it.

Two small covers in the front need to be removed. Deep inside are two 5mm bolts with T27 heads. The bottom screw is obvious and needs a washer (update on later saws) and to be secured with loctite 270.

I have a 361 muffler completely apart on my bench and I'm in the process of modifying it. Pictures and post to follow in a few days (just waiting for a part). I have figured out a simple way of adding a full-flow spark arrested port (not just a hole with a spark cover) without needing to uncrimp the muffler... but the internal pictures are very interesting. Big difference between this muffler and the older non-epa versions of the MS360.. and sadly a view of what is to come on the next generation of saws.

Andy, what must you do to the muffler in order to "mod it"? I would like to mod the muffler on my 034 Super but dont know how.

Originally Posted by Stihl4life

Andy, what must you do to the muffler in order to "mod it"? I would like to mod the muffler on my 034 Super but dont know how.

Not to step on Andy's toes, but I'm up at 2AM, so I'll give you my .02-

Put holes in it. It's got a two piece muffler like an 036, 044, 046, 066, which are are very easy to do. Remove the front cover via the four T27 Torx screws and drill holes in it. Do a search on this site for "muffler mod" or something to that effect. There's various opinions on how much air to let through, so you can make up your own mind on that after reading. The general consensus is anywhere from 85%-125% of the exhaust port at the cylinder wall. You can add a spark arrestor as well if you like. Not a bad idea if you're going to be cutting anywhere other than your back yard in the dry season.

Jeff

Originally Posted by Stihl4life

Andy, what must you do to the muffler in order to "mod it"? I would like to mod the muffler on my 034 Super but dont know how.

Good timing! I'm modding my 034 muffler this weekend. My first challenge is that the previous owner welded the front cover onto the muffler - it makes getting at the internal screws a challenge!

The postion of a second muffler port should be thought about. I don't want a port in the front of the muffler as it will get damaged when pressed up against a tree (the 361 muffler front is flush with the front of the saw already), must not interfere with the brake handle, push exhaust back to the operator, or onto hands when the saw is used on its side.

The issue of the spark arrester is a problem. If you need one for the area you live (or ANY western Forest Service land) simple drilling a hole and putting the screen over it is not a good solution. Sure it will arrest sparks, but will kill your exhaust flow over time. I'm a firm believer in having a screen not only for spark arresting, but to stop crud getting back into the muffler when the saw is NOT in use and subject to the muck of logging...

Screens are typically 40% obscuration (the wires) and tiny particles that cling immediately start reducing the output. If you look at the screen under a microscope even a "clean" screen that's been in use is reduced in though put considerably. Most good designs have a screen that is many times larger than the exhaust hole, and the screen is spaced back from the hole. Just making the exhaust hole larger isn't a good solution because it affects the tuning which will now vary as the screen blocks. It's a PITA to mod a muffler with a decent large replaceable screen with carriers, slots etc etc, but I do have a very simple off-the-shelf solution which you'll see in a few days.

The 361 and 036 (just two examples; there are many more) have a large screen and a small exhaust.

036 screen: 31x25mm = 775 sq mm. Exhaust hole (round plus slot) area - 113 sq mm...

361 screen: 36 x16 = 576 sq mm. Exhaust hole area - 63.6 sq mm (Damn, that's small... How do they get such good performance from 9mm round exit?)

Exhaust area AT the cylinder wall of the 036 is 327 sq mm. The 361 looks similar, but I need to get inside to measure it to be sure.

So.. the 85% number that gets batted around... maybe for some race machine, but for a woods machine, I don't think you need it even close to this. On the 036, this would be the same a having a 20mm round hole in the muffler. At some point all you get is more noise and you run out of the carbs ability to deliver enough gas!

On the 361, I'm going to start by taking the the output area from 64 sqmm to about 142sq mm TOTAL (leaving the existing port). I'm going to mod a second muffler that has an output area of 217sqmm, and compare. I'm betting there will be little to no difference in cut speed between the two modded mufflers.


For now, here's the pictures of the inside of the 361 muffler.



This is the entire muffler. Note the two plugs in the front. These are rusted in to the point where they need to be drilled out. PITA. The updated plug is a nice three-flanged device that is much easier to remove.





Opening the muffler... lever up up the heated crimp with a screw driver..



This is the inside looking towards the front. The cage and spark arrester assembly is all stainless. The tube (bottom left) intersects with the hole at the back of the muffler to exit. It's 9mm (inside) diameter.





Looking to the back of the muffler:






What about the internal cage? Forget it. It has plenty of area - over 470 sq mm of holes already!


If you don't want a spark arrester, the solution is easy - just uncrimp the muffler, chop off the internal pipe and grind away the inside edge of the output hole to the size you want.


My solution will allow a removable spark arrester, no material flow restriction over time, no need to uncrimp the muffler and about 20 minutes work (if that). Give me a few days...

I called WALKERS SAW SHOP about modding the muffler my 660, after talking to the "muffler mod man" , he told me basically the same thing Jeff said. Drill 2, 5/16" holes in the end of the baffle box. Then enlarge the exhaust hole in the muffler a little bit. To take it a step further, he gave me a part number for a front cover with a exhaust port in it. I didn't want the baffle in there so I went to my friends shop and ground the most of it out instead of drilling. Didn't order the cover though. Think I will just have my friend braze the pipes on later. Sure helped but, the dual port is the best bet. IMHO. Reason being when Walkers did my 372, it really came to life. Here are a few of Walkers mufflers.

Originally Posted by Stihl4life

Andy, what must you do to the muffler in order to "mod it"? I would like to mod the muffler on my 034 Super but dont know how.

That one is pretty easy.. but not optimal. Take off the front cover, take out the screen, and drill a few (I'd use 3) 5/16 holes in the raised section on the inside. Don't drill though to the outside. Clean out the metal bits!. I assume you have the version with a series of holes at right angels to the cover? Lever up the external guard and punch the internal deflector out somewhat using your newly drilled holes for access. Put the screen back in.

retune your carb!

Originally Posted by jack-the-ripper

I called WALKERS SAW SHOP about modding the muffler my 660, after talking to the "muffler mod man" , he told me basically the same thing Jeff said. Drill 2, 5/16" holes in the end of the baffle box. Then enlarge the exhaust hole in the muffler a little bit. To take it a step further, he gave me a part number for a front cover with a exhaust port in it. I didn't want the baffle in there so I went to my friends shop and ground the most of it out instead of drilling. Didn't order the cover though. Think I will just have my friend braze the pipes on later. Sure helped but, the dual port is the best bet. IMHO. Reason being when Walkers did my 372, it really came to life. Here are a few of Walkers mufflers.

I just ignored the existing hole on my 066 and added the factory dual port. It's SO much larger than the original that modding the original makes no difference. I published the measurements of the various original exhaust sizes and the dimensions of the factory dual port some time back.


Here's an extract from the orginal thread:




The standard muffler on a USA post 1998 066 or MS660 has an exit hole of 0.43 inch diameter. Prior to 1998, this was 0.63 inch. In 1998 they also made changes to the cylinder porting to reduce emissions (not sure what they did).

The USA Magnum muffler front has a internal rectangular hole (with rounded ends) of 1/2 x 1 9/16 inches feeding an external slot of 5/16 x 1 1/2.


So, area of outlet:

Prior 1998 : 0.311 square inches
Post 1998 : 0.145 square inches

Add a Magnum muffler front to either : add 0.469 inches... (and it might be a tad more than this).

Yes, the saw winds up pretty good with a magnum front and you have to remove and reset the limiter caps to richen the carb.

The internal box with all the smaller holes in it is the same for all the 066 mufflers.

That Post 1998 size sure seems puny in comparison to the other numbers!

NOTE: anyone messing with an earlier 066 muffler needs to make sure they have a main carb jet of at least .72mm. The "red eye" 066's had a main jet of .66mm (because the ignition limited the max rpm). Stihl published a tech note to say that using the .66 jet and turning up the rpm will result in piston seizure... as the saw couldn't get enough gas at high rpm.



If you want a screen, the "factory" option from 1995 is the way to go on the 660.. and if you have a cage, yes, drill out the end a little.

Originally Posted by Ax-man

From the looks of that muffler he won't have to richen it after the muffler mod. Thatt saw is running plenty rich

Larry

Not so sure... I look in the exit pipe and at the "hot areas".

The soot in the back was from my mapp gas buring up old crap, and the "wet look" is from my bucket of water

However...

That 361 muffler was from a saw used in a lumber yard for cutting beams to length for the customers. 100+ starts per day, never runs for more than 30 seconds... These guys are really hard on their saws. !

Ok guys, thanks for the advice. My only question is this: I am a motorcycle guy, and when you would adjust the carb, you would re-jet it. Meaning buying new jets. What would i want to do to the carb after drilling some holes in my muffler?

Originally Posted by Stihl4life

Ok guys, thanks for the advice. My only question is this: I am a motorcycle guy, and when you would adjust the carb, you would re-jet it. Meaning buying new jets. What would i want to do to the carb after drilling some holes in my muffler?

On your 034 super, assuming it has the C3A-S4 carb or similar, you won't have to re-jet it. Just adjust the H screw richer (counter-clockwise). You might need to adjust the L screw also for stable idle. Don't over-do the muffler mod - you can always add more area later and it's easier than putting it back!

Thanks! I drilled thee 1\4" holes in it and it will pull a 28" bar through hard maple no problem!

How do i mod the muffler on a Husqvarna 371XP? My friend has one and he asked me how to do it.

Originally Posted by sawn_penn

Good timing! I'm modding my 034 muffler this weekend. My first challenge is that the previous owner welded the front cover onto the muffler - it makes getting at the internal screws a challenge!

OK... I got the muffler off, which was quite a trick given that the torx screws were inside the welded-shut muffler.

So I now had a muffler with two screws rattling inside it. I tried to cut the welds out with a dremel, but I made a mess of the job. I ended up cutting the front off the muffler with a 4" angle grinder.

I left the cage alone, and welded a new front on the muffler. Two 3/8 holes and a couple of short pipes to bring the exhaust forward.

A quick retune and everything is running great. 20% faster and 100% louder!