Muffler Mod basics

[WadePatton]

I've got a 024 super, 2145, 2150, and a 2077 (in a few days) to play with.

I have some hot-rodding experience in 4-stroke, turbo diesels. My truck runs straight 4-inch exhaust off the turbo into 5-inch stacks. VERY little restriction except for the turbocharger. Keeps exhaust gas temps manageable, but is quite the loud thing. (all my trucks are well over 2x stock HP-dyno'ed).

NOW on the two-stroke, is less restriction always better, or is some control over the exhaust gasses good for performance?

 

[timberwolf]

Search the site on muffler mods, there is lots of info.

Up to about 150% of the effective port areas is what I have found to be an advantage.

If you go too big your loosing fuel out the muffler by letting the out going charge get too far from the port too quickly and not be availible to be scavenged back in. Also low end and idle suffers.

 

[skwerl]

I've never seen a muffler with 150% of port area that ran well. IMO the ones done by the best saw builders are about 90%-120% of exhaust port area (not counting the resistance added by the spark arresting screen). You can always drill a bigger hole, closing it up is harder.

 

[timberwolf]

Just read what I said, or do you just want to go on the attack first.

the word "About" and "up to 150%"

I have done this and measured saw and muffler temp, cut times, even fuel consumption.

From what I have found the saw runs just fine up to and maybe beyond 150% with no screen. However it burns more fuel and nets only a bit more cutting speed as the opening gets bigger from 100-150%

Just depends on what you want most of the max power with good idle and fuel consumption, or the fastest cut times to hell with fuel consumption, noise and what not.

I am also talking about effective port opening, which is a smaller number than just measuring the port with a ruler.

Based on the post was in response to a guy with hot rodded truck with 2x the HP and 4" straight exhaust, it would seem Wade is not too worried about the cost of saw gas.

 

[superman_36]

i use about 3/4 of the port as a good starting point +/-

 

[timberwolf]

3/4 of the port where it contacts the piston, or 3/4 of the port window where it connects to the muffler?

 

[WadePatton]

Yeah, I searched--but seems like every post has "muffler mod" in it.

And let me qualify my needs--mo power, but I'm not racing. Idle is good. Not concerned with fuel consumption--isn't that where power comes from?!

So what I'm saying is. I don't want to run the ragged edge, but would like to get up off the OEM/EPA BS spec.

 

[timberwolf]

http://www.arboristsite.com/showthread.php?t=6199&highlight=muffler+mod+260

Here is some old experimenting I did a couple years ago, I have done more messing with this since, but not bothered to put it together or post it.

 

[skwerl]

Check with a guy named Rich Hoffman (rahtreelimbs) here. He's been around modded saws for a long time and has been doing some muffler mods for a few members here. He's a perfectionist and they look good as well as work well. He's also fairly close to you in PA so shipping will be minimal.

 

[wagonwheeler]

Restriction varies w/ saw model and year. Some benefit greatly, some you'll never notice. No blanket solution.

Find someone who's successfully modded a muffler just like yours or proceed like Skwerl said - incrementally. It's not likely you'll kill the torque if you go slow and if there are no gains being made you can quit.

I suppose nearly any oversized muffler exhaust port can be closed down w/ a cover of some kind...but saves a step if you don't get there.

Chaser

 

[timberwolf]

Wade, just running more fuel through the saw does not get you mor unless it gets burnt.

If too much of the fuel charge gets out of the muffle during the BDC part of the stroke and does not get sucked or pushed back into the clyinder it just gets wasted into the ozone layer.

I would second skwerls tip, Rich is a likely a good guy to talk too.

 

[wagonwheeler]

http://www.arboristsite.com/showthread.php?t=6199&highlight=muffler+mod+260

Here is some old experimenting I did a couple years ago, I have done more messing with this since, but not bothered to put it together or post it.

Timberwolf, what did you mean exactly in step 5. Was the cylinder exhaust port at the muffler smaller than the muffler inlet port? Or the reverse (which would be bad)? Or were you increasing the port size all the way into the cylinder?

My 1998 025 muffler inlet port matched the cylinder exhaust port (at the muffler).

Just curious what you were matching and smoothing.

TIA

Chaser

 

[timberwolf]

I matched the muffler, gasket and outlet of the port window so that they matched as well as possible, the muffler and gasket were wider than the port window, but not quite as high, so I needed to work them all. It is likely not a big deal if the muffle side is bigger, but I was trying to be as scientific as possible.

In building pipes it is a concern if the header is bigger and poorly matched as this can cause waves to be partialy reflected as oposed to being constricted and directed back into the cylindar.

I did not at that time increase the port size all the way back to the piston, just blended things out.

 

[Lakeside53]

This thread like all similar threads in the past could go on forever, so let's solve that with an experiment.

Unless you know a lot more about the design of your saw than you do (solve that one!), the easiest way is to make a large ('ish) rectangular hole in the muffler, then cover it with an adjustable slide plate with a locking screw. Start small, increment indexed positions (like 1mm or whatever), and time your cuts. This way you won't be fooled that a loud saw cuts better.

Oh yes, post the results for all to see.

 

[timberwolf]

Sounds simple, but....

Each time the opening is changed the effective mixture after scavenging is changed, this was an error or an inconsistancy I intoduced in the experiment, I changed the mixture as the opening increased the rpm went up, this concerned me and I richened the HS.

So if you keep the jets the same the mixture becomes leaner as the hole opens, also as rpm and air flow increases the dynamics change in the carbs non liniar delivery curve.

If you re ajust jets each increment for the same RPM that will also put a wrench into the results.

Watching fuel consumtion is also very interesting.

I measured fuel consumption on muffler and pipe and found the saw actually burned less fuel per unit time on the pipe even though it cut 20-30% faster. Things that make you go hmmm...

 

[zimmy]

at the risk of sounding stupid does modding mufflers give an increase in hp but lessen torque the reason i ask is i have a standard 038m and a friend has a muffler modded 044 we both use 25 inch bars and rs chain but i can out cut him all the time even if we swap saws it does not make a difference if this is true why would one bother modding mufflers just trying to get my head around this

 

[Gypo Logger]

What from I can gather so far with muffler and cylinder alterations, it's a question of experimentation and no two saws will perform exactly the same with the same figures, but this is why it's so much fun to do.
In the pictured saw of the 385 I just built, I may have 100% of the exhaust port where it meets the piston, however, I did widen the exhaust port at the cylinder wall as well when I ported the saw. This also increases flow and another reason not to open the muffler too much as others have pointed out.
Along with opening the muffler, try to insure the gasket, heat flange and muffler fit together evenly so as to not inmpead exhaust flow.
John

 

[WadePatton]

at the risk of sounding stupid does modding mufflers give an increase in hp but lessen torque the reason i ask is i have a standard 038m and a friend has a muffler modded 044 we both use 25 inch bars and rs chain but i can out cut him all the time even if we swap saws it does not make a difference if this is true why would one bother modding mufflers just trying to get my head around this

From my school of reverse-engineering and 4-cycle preformance: The ratio between Horsepower and Torque are by design of the engine. In other words--UP one and you've upped the other. Also, air will never raise power unless unburnt fuel is present. Power is from fuel-fuel that burns.