Muffler Mods 1/2 the story?

[Chris-PA]

Does anyone know if that's a simple muffler or a cat? Because if it's a cat then there's a limit on how much you can enrich the mixture without making the cat get hot.

You should probably close those holes or make a deflector before it melts more plastic.

 

[BigMoneyGrip]

Two 3/16 holes do not equal one 3/8 hole. It would take more than four 3/16 holes to equal one 3/8 hole.

 

[nmurph]

Two 3/16 holes do not equal one 3/8 hole. It would take more than four 3/16 holes to equal one 3/8 hole.

........and four holes equal in size to one larger hole still does not flow an equal amount of air. The four holes will have more edge than a single hole of equal area, and that edge equals drag.

 

[BigMoneyGrip]

Yeah, the four 3/16 holes would have exactly twice the "edge" as the one 3/8.

 

[one.man.band]

ok.......this whole thing has got my attention now.

i dont really have the time, but now i'm going to take muffler off......split the muffler (cut in in half if i have too) and see what exactly is in there.>>>>>>>>>>thx sawinredneck

depending on what type of a baffle setup is in there .......i will probably weld up the stock and 2 extra holes i drilled....and make a side exit>>>>>> thx sunfish

.....and also measure the exhaust port.

ok...the for the size of 2 @ 3/16ths inch holes:

please realize that i do not yet know what is inside my muffler..but i will very soon. taking that into consideration....

edge?...not exactly understanding what you mean by that.

if the muffler is empty inside .... and exits through a 3/8" hole.....to the atmosphere......its completely different than exiting the cylinder through a length of 3/8" pipe. likewise for 1/2" or whatever. have to see whats inside.

as far as the 2@ 3/16ths holes:

experiment: take a 1/2 inch drill bit, scribe a line on it. roll it around once on a sheet of paper. mark with pencil dot where you start and stop.

then take a 3/16ths drill bit and roll it around two times (for the two holes i drilled with it).

you will find that the pencil dot marks, of the two 3/16th drill bit turns = 75% of the length between the single twist of the 1/2" hole.


blade<<<<<wtheck wrote that? oh it was me.....hahahahaha

 

[one.man.band]

husky 340e 41cc

almost done.

welding up the holes on top of muffler is taking much longer than i expected. the stamped steel muffler varies in wall thickness. especially on the chain side of the muffler where muffler wall is paper thin. it will be totally covered in slag before i finish. blowing holes through it. it got too late last night to finish.

using 0.035 mild shim stock 40amps 0.030 wire. welder cant go any lower.

what i found inside the muffler. nothing. no baffles at all. the only things that are inside...two sleeves for the mounting bolts.

factory stock muffler exit hole = 0.425 inch dia. = 0.14186 in2 (area)

exit port opening = 1.256 x 0.70
port area =0.8792 in2

so: roughly 16% stock


had to do some searching to find the bore and stroke for the 2.5 cuin motor. was wondering what the piston speed is in thing. piston speed using a couple of calculations was 2665.63 feet/minute at 12500rpm. not that it matters ...but that seems very conservative to me anyway.

piston speed = 0.166 x stoke in decimal inches x max. recommended rpm

---------------------------------------------------

what the plan is now:

relocate exit hole of muffler more in line with exit port.
increase hole size slowly.

figure out how the carb (HDA154C) works.

tune it. i am conservative when it comes to tuning because this is a saw i have to have for a while. still going to use plug color and CHT temp for tuning. 2 strokes plugs .... can be tough if you dont know what to look for. but this saw gets lots of hours on it ..and wont risk burning it up by not checking plug color and CHT.

 

[nmurph]

OMB, you are seriously overthinking this MM. Just make the existing opening about the same size as the exhaust port at the piston. Put the spark screen back on and you will be fine. I would not put the opening directly in front of the port. It will tend to burn the wood you are cutting, it will be louder, and will tend to lose more of the needed back pressure if pressure wave can go straight out of the front.

 

[PogoInTheWoods]

You really should read up on the "ear tuning" method. Lots of threads about it and it sure is faster and more reliable than using plug color. Too many variables with the latter. You could also use a tach, but after a MM it would only be a relative measurement since the specs should change (from stock specs) after a mod if the mod is significant enough.

Good luck and keep us posted.

Poge

 

[ratso]

One man band if I was close to where you live I would cut and buck all your 30" wood. Asking a 42cc to do the job pains me.

 

[sunfish]

relocate exit hole of muffler more in line with exit port.

Like nmurph said, do not do this. You want the exhaust to bounce around in the can. This is not a 4 stroke. Opening up the factory port to the size of the deflector is usually enough, or you can add another port to the front side of the muff.

There are many photos of MMs on the site, but ya gotta search.

 

[one.man.band]

its done.

right or wrong i dont know.

decided to change my new hole location after finishing welding. (after a break and cup of coffee!!!). to the right (chain) side of muffler about an inch down from top. at first i wanted it in the front, but changed mind because stamping is so thin, did not want a crack to start from a hole being between the mounting bolts.

glad i didn't after reading above replies.

0.825 x .650 (approx. 13/16 x 5/8)

61% now.

louder yes. still revs up ok without hesitation.

i know you want me to tune by ear pogo...... use what works for you. i am a meticulus 1/2 deaf old fart who trusts my eyes more than ears. my ears don't tell me if plug is fouling from a bad mix, overheating from running lean, etc.

jet turns: up 1/8 low speed, up almost up a 1/4 high speed. (starting from 1 1/4 turns out low, and 1 turn out high).

i put all the info i can on here so someone with a similar could learn from my mistakes.

hurricane irene forecast high wind 40+ mph and least 2 inches rain so far my way. hope everyone in its path makes out ok.

 

[nmurph]

make your hole bigger and trust your ears......1/8 turn might or might not be correct.....if you can hear the saw running you can hear when it is four-stroking.

 

[Chris-PA]

Like nmurph said, do not do this. You want the exhaust to bounce around in the can. This is not a 4 stroke. Opening up the factory port to the size of the deflector is usually enough, or you can add another port to the front side of the muff.

There are many photos of MMs on the site, but ya gotta search.

I agree too - if there's no baffle then all you have to do is open up an exit somewhere that won't melt parts of the saw, and preferably not where it's going to point straight at the wood. You don't need that much of an opening - it's a 40cc saw, there's a limit of what you can expect. How long a bar do you have on it?

My 40cc Husky 142 runs great with a muffler mod (still a pretty small outlet), but it's still a little saw. It's got a 16" bar, and I have no doubt it could pull an 18" if it had too, but you'll spend a very long time cutting up big diameter logs with it. I don't know if you have narrow kerf chain on it, but that would help a lot.

I would not tune using plug color either, as it's just the accumulation of everything the plug experienced from start to idle to full load. Plus it would be too slow. They're easy to tune by ear.

 

[eyolf]

Tuning by ear

Most of us that tune by ear (I admit that best method is an electronic tach) open up the main to abou 1-1/2 turns open, then turn it in by 1/8-turns until it will blubber a little at W.O.T. but clean up in the cut. You are running the saw just a bit rich in this condition, but that is a good thing for two reasons:

1) If you're an old hand at wrenching on engines you know that racers run their fuel-air ratios down to about 13:1 air/fuel by weight for best power It depends a little on the engine, but avarage 13.2:1 is max power: 14.8:1 is "stoiciometric", meaning just enough air for every fuel molecule at sea level, at 70 deg and 29.8" of mercury (like most of us will measure that when tuning our saws)
2) about 75% of the cooling in a two-stroke is the incoming fuel/air mix.

Opening up the muff WILL cause you to use more gas, partly because you'll be pumping more out into the atmosphere. AS you guessed, low end performance will drop off a little, but this isn't a concern on a powerplant meant to run at 8000 rpm and up. In my opinion, a saw meant to work every day shouldn't be opened up as radically as a "play" saw or racer. The big reason is that your ears will thank you, as well as your lungs. Saws running hard against a big log for long peroids of time make the user suck up a lot of fumes; half-burned gas, newer synthetic mix oils, and CO combine to give you a real headache.

The pumper carbs used on chain saws are a poster child for compromise: they have two circuits and can be tuned to idle well, to run at peak perfromance at W.O.T., but in between its a crapshoot. Engineers try to make certain they run a little rich at part throttle, but its usually not a good idea to test them out for long periods of time. Most carbs want to be set a little rich at idle to give a little headstart to the transistion phase. Off-idle fuel delivery is spotty, and there are no accelerator pumps. By the time the throttle plate is 1/3 opened and air is flowing through the carb enough to get the low-pressure area behind the venturi sucking fuel through the main system, the idle curcuit is not doing much...but you need it to work well until then, meaning a rich idle. On most saws you can screw the idle speed stop screw back until the saw barely runs, then turn the idle screw in and get a smoother idle...but open the throttle and it will die. Exactly where YOU like this compromise is somewhat personal preference, but keep it slow enough that the clutch doesn't engage, and rich enough that throttle response is good.

I have seen race saws and play saws with mods to the intake tract, but most working saws keep the stock airbox equipment for obvious reasons. One possible exception would be that some west-coast saw shops woul re-fit larger external air cleaners to working saws and Jonsered supplied some saws with a similar set-up as an option rght from the importer. Most of these parts came from concrete saws designed around similar frames as the chain saw, except some of the shrouding was removed. Newer saws with centrifugal dust-separation work so well that users are no longer demanding the big air cleaners on their chain saws, the E.P.A is getting sticky about non-stock equipment, so airbox mods are going away.

 

[one.man.band]

lots of info there!
i was hoping to understand the chainsaw fuel system better, thank you.

when i started this quest for more power, believed intake+ carb+ exhaust upgrades of saws were done at the same time. following suit with what i knew. thought that filter box/intake upgrade parts might be readily available.

never have i owned A/F meter guage. never knew exactly what my A/F ratio was. cars and bikes with carburators back then there were too many variables. float level, launch force, cylinders on right side over rich while left side lean (going circles), temperature and timing advance etc. it was a crapshoot at best. plug color got you close.

walbro chainsaw carbs and tuning:
tried to search for baseline settings of these carbs. on thier site mentioned anywhere from 1-1/4 to 4 turns out on the screws. not much help there. realize that my muffler ugrade is not radical, but possibility of a adjustment or jetting change. could find part numbers for jets, but no jet sizes listed or recommended for 40cc, 50cc ,70cc motors.

thinking was that if say, baseline turns out for my saw were 1-1/4 turns out low, and 1 turn out high....... would try to find jets that maintained close to the same baseline settings (turns out from needle seated) .....after the muffler upgrade. if the turns out changed to say 3 and 3 after upgrade, then would know that jet size(s) were too small.

on board with explanation of transition phase from low to high metering circuits of the carb. larger carbs (most) have some type of an air bleed circuit, (some with adjustable jets sizes, some fixed) to let you tune just how fast the high speed jet takes over.

adjusting a carb with just screws, makes me think that there will always be a 'flat spot' in the rpm range, no matter how many turns. thats where the air bleed helps things.

luckily, i did not run into any of this with just larger muffler hole......(or have to get out the jet drills)!!!

 

[trappermike]

When you "Open up" your muffler properly you should get a good power gain,but also you are accomplishing another really good thing-you are evacuating the heat out of the cylinder and engine much faster,upon a top end teardown I can see the piston has been running much cooler with less signs of overheating.In a motor with a really restrictive stock muffler you will often see signs of the piston overheating,PLUS a lot of carbon buildup on the piston crown and carbonizing around the rings and their grooves.
The best way that I modify any muffler,be it on a Stihl,Husky or any other is basically the same;
-I will order and use 2 of the "Deflectors" and screens from a 288 husky,they are worth the cost.
-Prepare to mount one on each side of the muffler at the front/top. Hold each deflector in place where you want to mount it,then using a small scribe,mark the inside of the deflector hole on the side of the muffler,because you are going to cut out the hole to full size before you attach the deflector and screen. I use a small tip on an acetelyne torch to cut out the hole,then finish trimming it nicely with a dremel. TIP- Don't use an actual acetelyne cutting torch,just use a small normal torch tip,turn it on to a normal flame,then start opening up the oxygen more until the flame is really "Hissing" and way oxygen rich,you have to turn the oxygen as high as possible to JUST BEFORE the flame "Pops" out. Now you have a really small,controllable cutting flame.You can easily cut the outlet holes out,but more importantly on the Stihl mufflers you can cut out any baffles and junk they have inside easily!
-Lastly,I lay my deflector(With the screen under it) in position on the muffler over the full-size hole I made and then I braze it down into place,both sides.
Then give the muffler a nice coat of high-heat(1500 degree) flat black paint.

I also use this method on the Husky 372 type muffler with the top outlet,so I end up with 3 outlets,works great.
I prefer to install the screens as I described for safety,they will never plug,and you can always wire brush them clean.
The 288 baffle just clears the chain brake handle on most models(Right side),and it directs the exaust away from melting anything.On the left side of the muffler you usually have to trim a small part of the top cover away to clear the baffle(Leave about 1/2" clearance),I mark it with a felt pen,cut it out with a hacksaw,and touch it up for a nice finish with a file.

This style muffler really roars and makes impressive power. If you if you follow this method you have a nice professional looking muffler with a somewhat factory appearance!:msp_thumbup:

 

[trappermike]

By the way....
Yes,the 288 baffle has 2 screw holes to mount it on. I don't use them,the 2 screw mounting is far too flimsy,and you will lose your baffles and screens,or be perpetually tightening them.
I braze the baffles on all around and they are secure forever.

 

[one.man.band]

great idea!
did not know that seperate muff parts were available. currently am running the saw with no screen. test cut saw buried into my ash tree stump. the hole exit points just over the top right of chain. its blowing dust everywhere.....very loudly i might add!!

question: bad to run saw without screen?

could not reuse original screen. tried to tack screen onto muff with some shim stock i had left over, but did not want to burn another hole through thin area of steel adjacent to exit hole.

75F afternoon after a straight 1 tankfull fuel run: outside cylinder temperature was reading between 193F to 210F (Taken at various points along cylinder). muffler temp was 213F. measured with fluke ir thermo. not probe. results cool very cool. did not measure temps before opening muffler.

rpm: saw gained rpm. running saw with 18 inch bar. my saw has automatic oiler. non-adjustable. worried now that oiler cannot keep up. paint is now melting away where it did not previous to opening muffler up.

question: should i be worried about burning up bars? are there oiler pumps/bleeds or whatever that will let me turn oiler into adjustable fromother model saws?

bought saw new in 2005. no manual/parts list. requested 18" bar. found out after i burned my first bar that they gave me a .058 bar with a .050 chain. banana cuts as well.

 

[trappermike]

I prefer to always install the screens. When the muffler is breathing well,the screens won't plug or impair performance at all. I don't want to cause a fire in my yard or be responsible for a forest fire!
Be sure youre muffler outlets are directing heat away from any part of your saw. I sometimes use a heat-reflecting stick-on foil to protect some part of the saw from heat,these I get from the 084 Stihl parts book,they are on the crankcase under the muffler,to protect the crankcase gasket from frying and then leaking the chain oil tank out.
If the muffler screen is known to clog often on a particular model of equipment,it simply means the muffler is too restrictive and needs a little work.
Also it's one thing for a faller to have a loud saw out in the middle of nowhere,it's another thing to have something sceaming loud in town and angering your neighbors,or police! Use discretion and don't torture others needlessly.
I almost got in trouble a couple of times test running saws with an expansion chamber(Racing pipe),too close to other people,I understand their disapproval now...I liked the racket,they didn't.