Lakeside53's --361 muffler mod w/photos

[rmihalek]

Remember to back out the high speed jet a quarter turn or so after opening up the muffler. The idea is to burn more fuel to make more power, so you have to let more fuel flow through the carb.

 

[twoodward15]

Exactly. I actually did a complete retune. I needed a very minor adjustment on my idle and low speed screw and a slightly bigger adjustment on the high speed screw. She runs good now and I can't wait to try it out.

 

[timberwolf]

Sounds about right, the extra LS and HS jetting is needed to make up not so much for the saw buring more fuel, but to make up for fuel being wasted.

The carb makes up for the extra fuel being burned. As air flow is increased, more fuel is drawn into the carb bore. The proof of that is how a saw will run on pipe or opened muffler with little or no change to jetting, more air is pumped by the engine, but more fuel is drawn by the increased air flow in the carb.

The price of power.:rockn:

 

[Lakeside53]

Wolf is totally correct! the converse is the EPA mufflers are heavily constrained such that you don't spew (as much) unburnt hydrocarbons in the environment.

The price of clean air or, get a 441.. or 575 or ...

 

[aquan8tor]

I searched around a bit, but couldnt find it, so here goes:

Anybody know how much you can open up the exhaust on the muffler of an 029S farmboss?? Its actually my dad's saw; I just use it more than he does.

Even with a fresh plug and a clean adjusted carb, the acceleration is suck-a$$. The little 024av that I opened up has faster acceleration!. The outlet of the 029S is roughly 1/2" square.
I figure lots of people must have done this one, b/c its a relatively popular saw.

 

[twoodward15]

My Homelite PS33 muffler mod was easy and way way way out performs the stock saw. I can't believe how fast this saw cuts now as compared to stock. It amazes me how much better it runs and cuts. It is definately louder. I have a friend with a couple shindaiwas and it sounds like his 375. I see a saw race coming up in the near future!!!

 

[CUCV]

Four Paws do you think my outlet area is to big for a 372xpg ????

I have been interested in seeing Four Paws response to this question.

I have been thinking about DP one of my 372 for a while and this thread has motivated me to get going on it.
Does anyone have the stock 372 exhaust port area calculated (Or other saws for that matter)?
I came up with 0.504in^2 for the 372. I measured the muffler hole to be 5/8" so the area is 0.307in^2. Thus using the 80%-85% rule the additional dual port muffler hole should be between .4" to .44" in Diameter (area between 0.125in^2 to 0.152in^2.)

So it seems to me like 2 additional 16mm ID holes are to much increasing the muffler exhaust hole area by 0.311in^2 each. That is unless the exhaust port has been ported.

That leads me to another question. Does anyone have any advise or recommendations on porting and polishing a 372? I remember a while back reading a good thread on 372 porting but either I can't find it or it has been deleted.

 

[CUCV]

Opps made a typo

I calculated 372 exhaust port area at 0.54in^2 not 0.504in^2.

 

[JUDGE1162]

Opps made a typo

I calculated 372 exhaust port area at 0.54in^2 not 0.504in^2.

How did you go about calculating the exhaust port area????

I keep read like you that the muffler opening should be 80% of the exhaust port area, but not sure how to calculate it.

 

[Four Paws]

I have been interested in seeing Four Paws response to this question.

I have been thinking about DP one of my 372 for a while and this thread has motivated me to get going on it.
Does anyone have the stock 372 exhaust port area calculated (Or other saws for that matter)?
I came up with 0.504in^2 for the 372. I measured the muffler hole to be 5/8" so the area is 0.307in^2. Thus using the 80%-85% rule the additional dual port muffler hole should be between .4" to .44" in Diameter (area between 0.125in^2 to 0.152in^2.)

So it seems to me like 2 additional 16mm ID holes are to much increasing the muffler exhaust hole area by 0.311in^2 each. That is unless the exhaust port has been ported.

That leads me to another question. Does anyone have any advise or recommendations on porting and polishing a 372? I remember a while back reading a good thread on 372 porting but either I can't find it or it has been deleted.

The 80-85% I stated is a safety blanket statement. It is possible that you can take the muffler too far on any saw. You will get louder, but you will get no more power, and at times make your saws power flat on top. Two stroke engines need back-pressure to function - too much back pressure and they are stuffed up and not running optimal, too little back pressure and you are sending a LOT of your fresh charge (fuel+air = lots of waster power) out the exhaust.

On a 372 muffler, dual 1/2" ports would be fine.

As for porting and polishing a 372 - yeah, there are quite a few folks that have done it. It is likely THE MOST, or one of the most popular saws to mod. There are also some rough timing numbers floating around out there if you look hard enough. I wouldn't suggest porting a good saw yourself - at least not your first one. Port a Poulan Wildthingy that you pick up on eBay for $30 if you want to learn. 372 jugs aren't cheap! There is a LOT of good info out there, read and learn and be patient. A muffler mod is a good place to start. If you HAVE to have a woods port, give some of the saw builders a call. If you don't know who they are yet, you have more reading to do!

Josh

 

[CUCV]

How did you go about calculating the exhaust port area????

I took a piece of paper, put it inside the cylinder (cylinder off) then traced out the exhaust port. Then I took some measurements and started drawing in CAD. Once the CAD profile matched the trace I let CAD calculate the area.

 

[timberwolf]

CUCV, sounds like the area you measure may be off a bit, got to remember the port is a three dimentional opening in the saw, if you trace it an lay the paper flat and measure it the drawing will be wider than reality. Though making the mufler opening slightly more than .85 wont cause any major problems, you may even gain a little top end. I would not worry about it too much for calculating a muffler opening, but engine modifications it is worth considdering.

 

[JUDGE1162]

Is this something that is given by the manufactor some where like in a spec log or dealer/service manual?

 

[CUCV]

CUCV, sounds like the area you measure may be off a bit, got to remember the port is a three dimentional opening in the saw, if you trace it an lay the paper flat and measure it the drawing will be wider than reality. Though making the mufler opening slightly more than .85 wont cause any major problems, you may even gain a little top end. I would not worry about it too much for calculating a muffler opening, but engine modifications it is worth considdering.

I have been thinking the same thing. When I get a bit more time I will try to draw it up in 3D. Basically I was wondering if others got similar numbers, or have others gone through and figured it out. I figured if I went with the 80% number that should cover the error.

Any specific engine mods you would suggest, specifics..?

FYI, I have an 044 that Dean modded for me and I have a 288 that is ported but needs other mods like timing and DP.

 

[timberwolf]

Dropped a word there, I had not intended to sugest an engine mod, but was trying to say it is worth taking the 3 dimentional port area into consideration if doing engine mod calculations.

372 has been modded well, puts it in with a stock dual port 066 at least in smaller wood.

 

[brushswamper]

chainsaw mod

i genneraly gut the mufflers of all garbage that the factory thinks is nessary
i did this w:rockn: :rockn: :rockn: :rockn: :rockn: :rockn: :rockn: ith a new 55cc craftsman and believe me it really did run

 

[Gark]

029/MS290 revisited

Like aquan8tor was asking about, an 029S muffler mod has been done here:
http://www.arboristsite.com/showthread.php?t=15986
which is found by a search of "MS290 Muffler". Thanks to rahtreelimbs. That muffler looks identical to one on my MS290, but I don't think mine will be quite as radical as that one.

 

[aquan8tor]

Like aquan8tor was asking about, an 029S muffler mod has been done here:
http://www.arboristsite.com/showthread.php?t=15986
which is found by a search of "MS290 Muffler". Thanks to rahtreelimbs. That muffler looks identical to one on my MS290, but I don't think mine will be quite as radical as that one.

Thanks for the link. How much did you open yours up? Trying to stay functional---and I dont want to take any crap from Dad if he has problems with it. Thanks in advance.

 

[rahtreelimbs]

Be forewarned............when the 029/290 muffler is opened up like the one I did the saw is extremely loud!!!

This I can't explain...............with all the mufflers I have modded this is one of the loudest!!

 

[aquan8tor]

I opened the muffler of my 394XP a fair amount; it wasnt that noticeably different in volume. I suppose its more b/c it still (temporarily--until I have access to a mig welder) exits through the side. I'm going to put a 1" or 1.25" iron pipe elbow on it with a short pipe to divert the exhaust the he)) away from my face & hands while I'm milling with it. We'll see what it sounds like then. Then I can play with the port size a little more.