Saw rpm's with muffler mod

[Sparky_NY]

Have questions concerning muffler mods. The saws in question are stihl and 272XP husky, I recently got 2 of each. I have done a lot of reading here about muffler mods and did my saws in the traditional fashion, total outlet area about 80-90% of the port area.
What I have not found in my reading is info on setting the carbs after the mods. I would assume the original max rpm's would not be valid after a mod, am I wrong? Both the stihl's and the husky's say 13.5K out of wood, they have to be be set pretty rich to get the rpms down to that level, they peak around 14.5 the husky getting close to 15. I backed them both off 500rpm's from peak, is that reasonable?
I am running 24 inch bars if that matters.

 

[fishhuntcutwood]

How do they sound? How do they run? And most impotantly, how do they cut?

Which Stihl did you get?

After a muffler mod, the saw will run comfortably at a higher RPM as it should. All of my saws are muffler modded, and I tune them by ear, get them running properly...then come in with a tach, and make sure I'm not screaming along at an exceedingly high speed. I've got my 361 and 200T running at 14,500-14,800 or thereabouts. I start getting leery of speeds much above that.

I do run my 056 Mag at 15,200.....just kidding.

 

[Sparky_NY]

How do they sound? How do they run? And most impotantly, how do they cut?

Which Stihl did you get?

After a muffler mod, the saw will run comfortably at a higher RPM as it should. All of my saws are muffler modded, and I tune them by ear, get them running properly...then come in with a tach, and make sure I'm not screaming along at an exceedingly high speed. I've got my 361 and 200T running at 14,500-14,800 or thereabouts. I start getting leery of speeds much above that.

I do run my 056 Mag at 15,200.....just kidding.

The stihl's are both 044's I would say that in the wood I tested with, 18-20" dry white oak, the two saws cut about the same. Both with new 24" bars and new round full chisel chains. I would say they cut good, no bogging, rpms stay up at a nice level and chips fly. My previous saw was a 032 so these things seem like monsters in comparison.

The muffler mods... The stihl had a original hole of about 5/8 which was left alone and a 1/2 thinwall conduit added to the cover at the bottom corner.
The husky 272, the original side outlet was cut off and covered and two round outlets brazed to the cover corners about 7/16 ID. Got the idea for the husky from a friends 371XP that had two 3/4 outlets on the cover but looking inside the 371 has a exhaust port that is about 3/8 wider than that of the 272XP so I went with smaller outlet tubes.
Does 500 rpm below peak sound reasonable? Both are running around 14 now.

 

[fishhuntcutwood]

Does 500 rpm below peak sound reasonable? Both are running around 14 now.

What are you considering "peak?" Stihl's published RPM?

 

[Sparky_NY]

What are you considering "peak?" Stihl's published RPM?

No, peak rpms with tach, as you lean it out.... then richen it up about 500rpm's

 

[fishhuntcutwood]

Like I said before, I'll set mine to where they need to be by ear, and then check the RPM's. I don't base the saw's tuning off of numbers, I just use the numbers to ensure I'm not too fast/lean. But if it's tuned at 14,200, well then so be it. If it's tuned at 13,800, well so be it. Elevation, air temp, all that changes so I let the saw tell me when it's tuned. I don't tell it that it's tuned at 14,000. It may not be. Even though my speed is in the green, the saw may be running like crap.

 

[Lakeside53]

The max RPM is valid if you want the saw to last...

As Jeff said (something like this) ... Modded muffer or not, set it by tach. If you set it by ear, check it with a tach until you get a feel for the saw with its new "sound".

If you're racing, do whatever you want to win, but for a working saw, stay with the WOT max as specified.

 

[Sparky_NY]

The max RPM is valid if you want the saw to last...

As Jeff said (something like this) ... Modded muffer or not, set it by tach. If you set it by ear, check it with a tach until you get a feel for the saw with its new "sound".

If you're racing, do whatever you want to win, but for a working saw, stay with the WOT max as specified.

As I read it... he turns higher rpms, just checks with tach to make sure its not totally wild rpm's, end is running above normal spec WOT rpm's though.
It would make sense that exceeding the max spec'd rpm's on a routine basis would shorten life BUT... that spec is out of wood and about the only time it runs WOT out of wood is for tuning purposes. In the cut the rpm's would be well below factory spec max. No ????

I would expect RPM's both in and out of wood to increase with a muffler mod, its breathing better. The higher rpm's in wood is the desired result, the higher out of wood rpm's are a resultant byproduct. Thats my reasoning anyway.

The original question is how to tune the carb with a mod muffler vs a stock muffler. Stihl for example with a stock muffler says to peak the rpm's and then richen the mixture to bring it to the max rpm spec. A engine breathing that much better would have to be excessively richened up to get it back down to OEM spec I would think, it wants to wind now that its breathing better. Again, only my reasoning, which has been wrong many times.

 

[Lakeside53]

Just as I said before...

Tuning WOT sets the running (Cutting) MIXTURE... Just because it can go higher (LEANER)doesn't mean you should... Stay with the limits unless you don't care about your saw, or like melted pistons. Yes, you do need to richen the mixture with the muffler opened.

If you're really into the max performance, do timed cuts. Choose the richest setting for the best cut times, and... clean air fiters and sharp chains...

I run my saw below the max WOT. As Jeff points out, variables like weather, temperature, filters etc can conspire to push you way over if you are not careful. I'm just happy with my muffler gains as they are.

 

[fishhuntcutwood]

I just mentioned in the 390/361 thread, moderation is the key. I look at my muffler mods as a way to get back what the EPA and OSHA have taken away. I don't look to race saws. I just cut wood and make trees fall down. I do play it on the safe side, but I'm very comfortable letting my saw run faster than Stihl's posted specs, because Stihl's specs are specified with the cooped up muffler. I think about what the saw can handle. It can probably handle much more, but going from the factory spec of 14k (or whatever it is exactly) to something like 14,800 or whatever each of my saws runs at isn't that big of a deal. I could probably tune them up to 15k+ and get some super timed cuts, but I don't race, and as long as my saw can keep up in the backcut and not bog with the B&C I have in the tree I'm working, I'm happy. The saw runs cooler, turns a bit faster, and I'm happy.

Moderation and common sense go a long way in tuning a saw.

 

[fishhuntcutwood]

As Jeff said (something like this) ...

Is this worth a point for me Andy? If so, I have four now.

 

[Lakeside53]

Is this worth a point for me Andy? If so, I have four now.

Ok... if you insist, but I'll be watching you!

 

[Lakeside53]

.

Moderation and common sense go a long way in tuning a saw.

To those that haven't really watched a tach, the difference between say 14k and 14,500 is MAYBE a 1/16 of a turn (carb dependant) ... and if you check it 10 minutes later or the next day, it will vary 250-500 rpm +/- Max rpm spec is more about bearings, lubrication, flywheels, overall engine balance, chain speed and other design limits than just "power". I can turn a 200T up to 17K+, but I don't...

You're usually cutting on a mid-size saw at 8500 to say 10500 (varies by saw) so the actual WOT speed doesn't directly correlate. At some point you are too lean, too hot and cut times are going down... and in the blink of an eye, so can your wallet.

Just replaced a piston/cylinder in an 064 that has been "power tuned". "It was working so well before it wouldn't start again - just needs a tune up". Sure took a lot of aluminum of the exhaust edge at the top of the piston. Hmmm...

 

[RED-85-Z51]

ive got a little italian 1/5 scale touring car with a small 25cc 2 stroke on it, and it tached out at about 15K no load, tuned pipe and all.

Its a screamer, so far, Ive run it WOT at 15K for 10-15 seconds with no failures, it is mixed at 24:1, and running quite rich in fact, so rich, that I get alot of oil spatter out the stinger on the muffler..

Ill bet the little engine would make a heck of a saw engine....

HMMMMM....opcorn:

What is the maximum RPM these little engine can take before you get the "expensive noise"?

Ive had smaller, cheaper 2 strokes with the stamped rods die a tragic death at only 8-9K.

What is better, a muffler mod, or a tuned pipe?