Lakeside53's --361 muffler mod w/photos

[timberwolf]

Yes for a tube, for an orifice in thin plate no.

Problem is in smaller holes the thickness of plate in relation to the diamiter of the hole changes the coefficient of discharge to a greater extent than how much the wetted perimiter effects the total flow.

When the radius of the hole is only a few times greater than the tickness of the plate the coefficient of discharge starts to head more towards 0.75 instead of 0.60.

I even found that a thin slot with the same area as a circle flowed as much or more than the circle. in theroy looking at the wetted perimiter this should not be. However an orifice shaped as a thin slot in thin plate is squeezed between two edges that have a high relative thickness compaired to the width of the opening raising the coefficient of discharge.

I would not have though this would be, more wetted perimitter should be less flow from a simple logical prespective, but like I said putting this to test on a flow bench has taught me otherwise. In some cases esp in smaller openings coefficient of discharge is a bigger factor than wetted perimiter.

 

[BigSawMan]

Well I modded the 385, I drilled 4 1/4" holes spaced out evenly on the front of the muffler. I just drilled through the first piece, the outside of the muffler, should I drill out the inner baffle as well?

The coefficient of flow talk about the hole size vs the thickness of the metal makes me think that I should open the holes up a little bit more because they are smaller?

What do you guys think?

 

[timberwolf]

Four 1/4 inch holes is very conservative, that sort of opening would more suit a saw half the 385 size.

Go with a 3/8 drill, thats still under 0.5 in2 and is likely close to 100% or less of the stock exhaust port area.

Often the muffler insides are where the real restriction is.

 

[BigSawMan]

Well I'm going to drill out the holes to 3/8ths, should I drill through the second plate on the inside?

Would four 3/8ths holes be too much? thats equiv to 1.5" hole.

 

[timberwolf]

No 4 holes 3/8 each is fine, it is not equal to a 1.5 inch hole.

The area of a circular hole is half the diamiter x half the diamiter x 3.14

0.375 /2 = 0.1875

0.1875 x 0.1875 x 3.14 = 0.11 in2

0.11 in2 x 4 holes = 0.44 in2

Four 3/8 holes is equal size wise to a single 3/4 inch hole. A circle twice the diamiter has 4 times the area. A 1.5 inch hole then would have 4 times the area of four 3/8 holes.

Don't forget to reset the carb, bigger exhaust holes and it will need more fuel from richer jetting.

 

[BigSawMan]

Ahh, thanks for the math lesson lol, I thought that didnt sound right when I did the area in my head...

Will do.

 

[Dowclan]

036 -Muffler Mod

Hey guys, I've got a 036 and was wondering if it was worth the effort of muffler mod. I've read how it's the newer models that really benefit from the mod and I couldn't determine if the benefits would out weigh the cost/labor put into the effort. Thanks in advance for your thoughts.
Dave

 

[BigSawMan]

Do it!

Do a search for 036 or stihl muffler mod and see what comes up, I'm sure your not the first to do one.

How advanced do you want to go, just drill some holes or cut and weld in new tubing etc..?

 

[Dowclan]

Bsm

BigSawMan:
Thanks for the feedback. Yeah, I read nearly the entire thread. Heavy reading for sure. There's a section written specifically for the 361 owners. But since that is a newer saw than my 036, I wasn't sure if the outcome, would be as rewarding. I may consider it after I finish cutting some more wood this year.

 

[GrizzlyAdams86]

After reading this entire thread, the gears are turning in my head. I just got my 288xp going and would muffler modding/porting this be worthwhile? It has the larger dual felling spikes with the A/V bracket mounted to the muffler and was made sometime in the 90's. I also have a early Husky 61 (has the white top cover) and a 137 for practice/fooling around with if I decide to mod the 288. I primarly just cut firewood although in my area we've been losing some bigger oak, elm, and cottonwoods to disese, etc. Any and all comments are welcome. Thanks!

Husqvarna: 137, 61 (in pieces-yet), L65, 288xp, 2100CD
McCulloch: Mac 2-10 (won't stay running-rainy day project)

 

[(WLL)]

after failing several times trying to get a original wojo muffmodd i had to make my own. i thought i posted here a while back, but cant find it with search. this is what i came up with.

the biggest problem with the 066 is the carb needs more more fuel and the Onegin needs more air. if u open every thing up the rpm's will scream. imo the stihl is a better saw to work with and has a better/stronger chassis than the husky,better air flow than the husky,better jugs than the husky,better,ect,ect,. they are both top stock sawz to work with in wood,but stihl is the only saw for me. DONT BE A:monkey: iiMODDED SAWZ ARE DANGEROUS!!

 

[SawTroll]

I actually have a Andy made muffler that look a bit different - pics will show up some time, when I have put it on the saw.

Hard to get a decent test log here, the way my foot is - have to go into the woods, and the ancle is not stable......:censored:

 

[skinnykid02]

thats looks real nice! Will someone do that to mine??

 

[K9-Handler]

well i have put it my fair share of welding and i can't figure out why you couldn't braze this mapp gas burns a little less than acetylene and acetylene burns at 6000 degrees it could have been a lot of things wrong brazing rod improper hose pressure wrong size tip the list is endless.

The givaway is that he said it cost him $10.

I braze with Oxy/Mapp, as I'm sure you do, injun joe. I think he just went out and bought one of the hardware store yellow mapp cylinders and thinks it would get hot enough to braze. It won't.
All those things are good for is soldering pipe a little quicker than propane would do.

 

[Metals406]

Yes for a tube, for an orifice in thin plate no.

Problem is in smaller holes the thickness of plate in relation to the diamiter of the hole changes the coefficient of discharge to a greater extent than how much the wetted perimiter effects the total flow.

When the radius of the hole is only a few times greater than the tickness of the plate the coefficient of discharge starts to head more towards 0.75 instead of 0.60.

I even found that a thin slot with the same area as a circle flowed as much or more than the circle. in theroy looking at the wetted perimiter this should not be. However an orifice shaped as a thin slot in thin plate is squeezed between two edges that have a high relative thickness compaired to the width of the opening raising the coefficient of discharge.

I would not have though this would be, more wetted perimitter should be less flow from a simple logical prespective, but like I said putting this to test on a flow bench has taught me otherwise. In some cases esp in smaller openings coefficient of discharge is a bigger factor than wetted perimiter.

TW, so you're saying a slot port (as pictured below) would flow better than a round pipe?

 

[Lugnutz]

ok to be honest I haven't looked to find spark aresting mesh..thought it would be easier just to ask the people that know what they are doin...so..where do you find this stuff???

 

[Lugnutz]

Finally found it

After reading all 15 pages I found where to get the mesh. Took the muffler off my WildThang and found out I don't need any mesh, drilled 6 holes in baffel on the underside and a 3/8" hole in the front cover. Seems purdy snappy now and with some tinkering with the carb it idles nice once again.

My only question concerns how to tell if it is burning lean. I adjusted the hi end to max with the red plastic cap still on it. Am I going to only be able to tell by looking at the spark plug? Also how do you pull the caps off if you need to go further with it?

 

[Urbicide]

The limiter caps have "stops" which obviously block movement of the screws past a certain range. You will need to remove the actual tabs with a dremel, razor knife, or heavy duty nail clippers. You do not need to remove the whole limiter cap. The safest way to check RPM's is by using a tach. Madsen's has a nice section on saw tuning with some sound wave files to give you an idea of how a saw should sound.
http://www.madsens1.com/saw carb tune.htm
Scroll down to #6 under Carburetor Adjustment Procedure and you will find the high speed adjustment file.

 

[maytagman]

I am in a area that I am not worried about using a spark screen. If I did this mod and didn't want to use a screen would I use a smaller dia. pipe since you must figure the screen creates a certin amount of restriction?

 

[Lakeside53]

You can.... but why not just run a screen to deep the junk out...?

As for resizing... you can go down to 14mm if you like, but it works pretty well at 16 with no screen. Idle isn't as nice, but it's no big deal.