025 Muffler Mod (Pics)

Well, it isn't modded yet but this thread will hopefully be easy for others to find in the future and might even distill the info down to something less nebulous. There is a WIDE range of mod parameters in only a few prior posts.

Attached is a pic of my stock 025 muffler components and the stock port sizes. Outlet opening is 87% of inlet opening.

I've read that you want the outlet to be 70-85% in one thread (which mine already exceeds) and another thread said the outlet should be 125-150%.

One thread recommended creating a dual port by drilling four (4) 3/8" holes on the right side of the muffler and adding a screen and deflector for it. Which adds .44 sq.in. for a total outlet port of .99 sq.in. That is a 180% increase over the inlet port.

None of these have screen blockage broken out, but .99 sq.in. w/ a 40% blockage screen will net .594 sq.in. or 96% of inlet size.

Seems to be a consensus to either pry open or grind open the slits in the screen cover. Also to either drill the internal baffle holes larger or grind the face notch of the baffle back to the first set of holes.

It also seems that some later 025 carbs must have had a more restrictive outlet port under that screen? Anyone have an 025 or MS250 carb for comparison that differs?



Chaser

wagonwheeler said:

I've read that you want the outlet to be 70-85% in one thread (which mine already exceeds) and another thread said the outlet should be 125-150%.


Chaser

Click to expand...

Try 75%-85% of the exhaust port area at the cylinder wall, or, as it's easier to measure, 125% of the exhaust port at the muffler mount.

Don't you mean the other way arround?

125% of the effective port area at the piston or 75%-85% of the exhaust window where it connects to the muffler?

timberwolf said:

Don't you mean the other way arround?

125% of the effective port area at the piston or 75%-85% of the exhaust window where it connects to the muffler?

Click to expand...

YES! Damn fingers typing faster then my brain. Where's that coffee?

So I need to measure the exhaust port from 'inside' the cylinder? Else use the 75-85% at the exhaust window.

I'm already at 87% based off of measurements where the exhaust window connects to the muffler, and the gasket doesn't interfere into that opening.

This leads me to beleive the factory muffler is already opened sufficiently?

Chaser

sounds like it may be enough.

From what I have experienced if you make it too big low speed becomes unstable and fuel consumption goes up with no gain in output as fuel is lost in inefficient scavenging.

You may want to check your math from your earlier post.

One thread recommended creating a dual port by drilling four (4) 3/8" holes on the right side of the muffler and adding a screen and deflector for it. Which ADDS 1.77 sq.in. for a total outlet port of 2.31 sq.in. That is a 372% increase over the inlet port! What happens to backpressure?

Click to expand...

My math tells me 4 .375 holes adds up to about .44 sq.in. Square the radius not the diamiter?

yes, the 025 may be "optimal" already - it is the biggest of the 021/23/25 range.

However, one thing to remember is that the screen has a significant area that detracts from the muffler hole. Some screens are 43% BLOCKAGE. Not sure what an 025 screen is. An easy test to see if the saw will run better with a larger muffler hole is simply to take out the screen and do some timed cuts.

timberwolf said:

sounds like it may be enough.

My math tells me 4 .375 holes adds up to about .44 sq.in. Square the radius not the diamiter?

Click to expand...

You are correct. Much better! (I'll revise that for future clarity.)

Chaser

Lakeside53 said:

yes, the 025 may be "optimal" already - it is the biggest of the 021/23/25 range.

However, one thing to remember is that the screen has a significant area that detracts from the muffler hole. Some screens are 43% BLOCKAGE. Not sure what an 025 screen is. An easy test to see if the saw will run better with a larger muffler hole is simply to take out the screen and do some timed cuts.

Click to expand...

I agree. I had wondered this as the screen is most certainly not 100% open!

I'll do that first and then perhaps grind the notches in the internal baffle back to the first hole and see if that has any affect (which it likely will not).

It just seems like a pretty 'free' muffler already - except that screen.

Chaser

Take that basket and "lose" all the baffleing except for the tubes that the mounting bolts go thru!

Lose the screen as well.

bwalker said:

Lose the screen as well.

Click to expand...

And the screen cover w/ the slits is probably as bad a restrictor as that screen which compounds the problem. What good is an 87% outlet that's blocked off, right?

Chaser

I'd just leave it alone and cut wood.

Lakeside53 said:

I'd just leave it alone and cut wood.

Click to expand...

Free HP..........no way!!!

Lakeside53 said:

I'd just leave it alone and cut wood.

Click to expand...

Yeah, I expected to see a lot more restriction than was found just from all the posts about such. Maybe later mufflers and other models were/are worse.

Free HP from this 025 may be more akin to a 10% rebate than a buy one get one free...except that I don't even know what the percentages are...

I can make some cuts w/o screen, baffle, or screen cover (or any combo thereof) and easily see what kind of difference it makes, and can do so without any grinding or drilling. Simple enough to find out if more openness is something to pursue or not.

The MS440 I picked up today at first glance appeared to have about the same muffler inlet size as the 025 (no internals whatsoever in the muffler) and a surprisingly small outlet size and screen for a good bit larger saw. I didn't do any measuring, though, and area amount increases rapidly with seemingly small increases to opening size. But it was a reminder that later saws and different models may suffer more than others.

But that 440 won't benefit one bit from a muffler mod...since it don't run!


Chaser

Outlet Area

Chaser , what is the outlet area (louvre) compared to the cylinder exhaust port area ?

scottr said:

Chaser , what is the outlet area (louvre) compared to the cylinder exhaust port area ?

Click to expand...

Dunno that or the screen effective outlet area.

I'll try and determine the louvre area. But that's what had me thinking I could just leave them off (along w/ the screen) and make some cuts after adjusting the carb.

I could even remove the screen and put the louvre back on.

Chaser

Bottle neck

My guess from looking at your 025 muffler is that the louvre open area is the exhaust flow limiting component . The screen although it's probably 51% to maybe 71% open has a much larger open area than the three small louvres .

Observations after some cuts.

Well I'm now satisfied that this 025 is not suffering from a rich non-adjust carb or a restrictive muffler.

I took it out and made LOTS of cuts thru 11" round gum. And though there may be some SLIGHT change, it is not perceptible. And these cuts were 11sec cuts, so there was plenty of 'time' to notice changes.

I was using a digital timer, just letting it run constant, and would start my cuts on any multiple of 10. Not exact, but easily within .25sec or so.

I first ran the adjustable walbro 215 w/ the stock config muffler. 11 sec.
I then ran the walbro 215 w/ baffle, screen, and louvre removed. 11 sec.
I then ran the walbro 215 w/ louvre replaced. 11 sec.
I then put the muffler back together and put the NON-adjustable carb back on. 11 sec.

I did adjust the carb to where a 1/16th turn would take it in and out of 4-stroking for all cuts.

This 025 really does run well and was throwing a fountain of big chips (RS chain). As far as I'm concerned gains that obscure are more theoretical than practical. I'm satisfied w/ the 025 for what I'll be using it for. It's not robbing me of anything.

For comparison I ran some cuts w/ the 361. Consistent cuts that barely made 5 sec.(high 4's). Even w/ the limiter caps I could lean it out of 4-stroking and so I tweaked it and kept it safe.

I'm impressed that from 44cc to 59cc means half the time in 11" wood. Makes me wonder if a 460 would halve that or if you must move up to bigger wood to keep halving the cut time.

It does appear that my 025 muffler is PLENTY open already. I compared it w/ the MS440 muffler outlet and the 025 has MORE outlet are. So this little 44cc saw is doing fine. And I'm also impressed w/ the non-adjust carb. Couldn't improve cut times over it and it's not too lean - which is important.

Anyway, it was fun. This is a handy combo...until something bigger comes along...

Lakeside53 said it well...'leave it alone and just cut wood."

It's nice to confirm any doubts, too.

Chaser

025 Louvre area

I'm following up my followup since there was a question as to what the area of the louvres on my 025 muffler was and I wanted to include it here.

Two of the louvres are approx .095in x .530in = .050 sq.in. each = .100 for the pair.

The third louvre is a modified triangle w/ interpolated base and side approx. .230 and .520. So an approx area of .060.

Total louvre exit area is approx. .160 sq.in. There is some additional leakage around it's perimeter since it is not sealed, but I didn't try and put any number on it.

The 025 muffler outlet port was .546 sq.in. so this louvre area is quite a bit smaller. Even considering screen restriction at the outlet port, the louvre area is going to be the most restrictive part.

By comparison, the MS440 muffler I've got has a muffler outlet port w/ a .40in. dia. So that outlet area is .126 sq.in. at the port.

That's smaller than the 025 louvre open area and WAY smaller than the 025 muffler port! But there is a lot of screen behind that little hole, so enlarging the MS440 outlet area would be easy.

Chaser