I'd like to take a look at the flat-rate book (if there even is one...) and calcualte how many man-hours you put into modding/unmodding the thing and extropolate how many 11 second cuts into the 11" gum you could have made in that time! HA! Just yanking ya, wagon - thanks for the research and report - seems sometimes things are just OK enough how you find them. Good for you to look into it, and REAL good to honestly report that no real-world gains could be had with the various configurations at hand.
025 Muffler Mod (Pics)
- Thread starter wagonwheeler
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buck futter
ArboristSite Guru
What year was your 025 manufactured? I bought mine in 2002 and off the cuff I would say that the outlet port on your muffler looks larger I will measure mine and let you know what I have for dimensions.
Lucky
AKA Buck
Lucky
AKA Buck
ErrolC
ArboristSite Operative
I've been bitting my lip and holding off long enough...Just cut the louvers out all together.
Theres a lot more to what you're doing than you think and what isn't being considered here is the dynamics of the gases passing through your ports and muffler baffles. Heres a small example to consider.
If you watch water flow into and through a drain pipe (or dam channel) note how the water bunches up at the entrance and squeases through to drop down as it passes the opening...same thing is happening with the louvers (just what are they there for anyway...to reflect and break up the pulse of the exhaust to cut noise) which causes back pressure. How ever dropping back pressure will have its limits as well to a point where you can actually start to loose power through purging inlet charge out the exh port (thats where expansion chambers come in)...then you get into changing, in this case, exh port timing... and getting more gas into the cylinders through the transfer ports (another issue)...anyway in a nut shell twice the pipe area will pass more than twice the flow all other things being equal (to do with whats called a scale effect). This means that the numerous louvers of a similar area to the single port will not flow nearly as well, as the port...when the louvered sector needs to flow significantly more due in part to shape and design restrictions.
Whats more important where the port area is limited (due to cylinder wall having to support the piston ring from popping into the port) is the shape of the port and where you design that area into the port...in the exh port the top of the port flows much more than the bottom due to it being exposed to the gas flow for a much longer period...this is the area of best return to mod for port window area...before you get into the port tunnel itself...that gets a little more involved.
find a good book on two stroke design...it'll get you on along road of discovery
Theres a lot more to what you're doing than you think and what isn't being considered here is the dynamics of the gases passing through your ports and muffler baffles. Heres a small example to consider.
If you watch water flow into and through a drain pipe (or dam channel) note how the water bunches up at the entrance and squeases through to drop down as it passes the opening...same thing is happening with the louvers (just what are they there for anyway...to reflect and break up the pulse of the exhaust to cut noise) which causes back pressure. How ever dropping back pressure will have its limits as well to a point where you can actually start to loose power through purging inlet charge out the exh port (thats where expansion chambers come in)...then you get into changing, in this case, exh port timing... and getting more gas into the cylinders through the transfer ports (another issue)...anyway in a nut shell twice the pipe area will pass more than twice the flow all other things being equal (to do with whats called a scale effect). This means that the numerous louvers of a similar area to the single port will not flow nearly as well, as the port...when the louvered sector needs to flow significantly more due in part to shape and design restrictions.
Whats more important where the port area is limited (due to cylinder wall having to support the piston ring from popping into the port) is the shape of the port and where you design that area into the port...in the exh port the top of the port flows much more than the bottom due to it being exposed to the gas flow for a much longer period...this is the area of best return to mod for port window area...before you get into the port tunnel itself...that gets a little more involved.
find a good book on two stroke design...it'll get you on along road of discovery
wagonwheeler
ArboristSite Guru
ErrolC said:
I hear what your saying but can't go anywhere with it. How can "cut the louvers out altogether" be more precise? Do you know I'll do exactly what you expect? You've given a very detailed and at the same time vague description.
How did you arrive at this being the solution for my 025? Do you absolutely know for sure it even needs this much area (however much area you mean)?
Show your math and tell me the actual area needed at the louvres, otherwise your advise is of no use to me. How could it be? I'm not convinced this muffler is restricting the little 025 motor, no more air than it moves.
Chaser
wagonwheeler
ArboristSite Guru
lucky001 said:
Just heard from Stihl. Mine was first registered in March 1998. So production was likely mid-late 1997. Mine sure doesn't look 8yrs old. Still has the paper sticker totally intact on the front of the case below the muffler...
Chaser
buck futter
ArboristSite Guru
my measurements
My cylinder outlet width was 15/16 or probably some metric standard close to that, the height at the cylinder wall was tough to get and may not be exact but it came out to about 9/16. The bottom of the port slopes down and it is kind of tough to get in there. 15/16 * 9/16 =.5273 sq. in.
I have already modded my muffler and the height was 15/32 and the width was 7/8. 15/32 * 7/8 = .41015 sq. in
.41015 / .5273 = 77.8%
this is modded and is still smaller than what your stock opening is. I wonder now if I should open up the muffler more to match you numbers? Did stihl have yours at the best workable numbers and ratio? Also I had opened up the holes in the basket would you measure what size holes are in yours please.
I wish I had the original measurements of the outlet hole of the muffler, I think it was around 45% off the top of my head.
I was kind of excited when I did my measurements and saw just how much the epa has changed things.
The next part we will probably never know. If we have the same saw with the same 3.0 bhp but the epa choked my muffler. What happened did mine get better porting to compensate and then with a muffler mod come out a little stronger? Did I not have the advertise power or did I have the advertised power and you had more? Also I wish I could compare the sound pressure specs of the different years, was yours any louder than mine? I guess we will never know.
Lucky
AKA Buck
My cylinder outlet width was 15/16 or probably some metric standard close to that, the height at the cylinder wall was tough to get and may not be exact but it came out to about 9/16. The bottom of the port slopes down and it is kind of tough to get in there. 15/16 * 9/16 =.5273 sq. in.
I have already modded my muffler and the height was 15/32 and the width was 7/8. 15/32 * 7/8 = .41015 sq. in
.41015 / .5273 = 77.8%
this is modded and is still smaller than what your stock opening is. I wonder now if I should open up the muffler more to match you numbers? Did stihl have yours at the best workable numbers and ratio? Also I had opened up the holes in the basket would you measure what size holes are in yours please.
I wish I had the original measurements of the outlet hole of the muffler, I think it was around 45% off the top of my head.
I was kind of excited when I did my measurements and saw just how much the epa has changed things.
The next part we will probably never know. If we have the same saw with the same 3.0 bhp but the epa choked my muffler. What happened did mine get better porting to compensate and then with a muffler mod come out a little stronger? Did I not have the advertise power or did I have the advertised power and you had more? Also I wish I could compare the sound pressure specs of the different years, was yours any louder than mine? I guess we will never know.
Lucky
AKA Buck
