muffler modding 661 mtronic advice needed

so what's the word on opening up mufflers on mtronics ? I was thinking about opening up the hole to the size of the deflector and then recalibrating. Naturally I don't want to poof my saw but it sure seems restricted and hot.
What have you all been doing?

 

Next time I’m down in the shop , I’ll pop mine off for some pics . Most likely tomorrow A.M. .

 

Should be easy-peasy. M-tronic will keep if from "poofing" i.e. burning up from running too lean. Def. enlist experience on how much to open it for optimal results.

 

You can drill the spot welds and remove the baffle, open behind the stock deflector, and add a small deflector on the recoil side. That would help

 

And then recalibrate it, correct?

 

Thanks, no rush on my end just trying to get a plan.

 

I'm spooked by the possibility of pizzing of the computer.

 

um 1140910, member: 4169"]I'm spooked by the possibility of pizzing of the computer.[/QUOTE]
No worries there. The computer will re-tune by itself after any muffler mod.

 

You can. If it’s the newer 661 with the V3 coil and solenoid on it, it will calibrate the saw to your new given parameters. On the older saws, it resets the M Tronic to factory specs and starts to learn again

 

Here you are . The paper is 3” wide , marked at 1/2, and 1” for scale .

 

I'm gonna be doing a MM on my new 362 CM soon and was wondering what you guys reccommend for the ratio of the muffler output area to the input area. I've heard two schools of thought on this, output at 70% of input area and others that say to open the muffler output up to 120% more than the muffler input. The others I've done have been in the 70% ish size and have made nice improvements in cut speed, but I'd like to hear a little of the theory behind the number instead of just the number.

I'm not racing, but sure do like to get the most out of my firewood saws without getting radical or spending a bunch o' cash... Someday I'll send a saw off to get ported, but cash flow restrictions are the main issue for now. Laying down the cash for a new saw was a big step for me at this point but I've been wanting / needing to step into the pro series.

 

Thank you. I just don't know much about the mtronic, a bit confused about how it works without monitoring the exhaust.

 

Thanks for the pics and the scale sheet helps out. So the screen is just kept in by the bent tabs ?

 

I did my 362CM. Easy job. I just added a hole next to the factory outlet. She's a ripper.

Easy MS 362CM Muffler Mod

 

Yes , the screen is kept in with those tabs .

 

I’ve read 80% probably more than any other percentage . But , I don’t think it’s all that critical .
My MS 460 is opened up more than the 661 , and it’s happy to idle , transition ,and run at W/O throttle .

 

I can't remember what the factor is, but I know the spark arrestor screen reduces the effective opening by quite a bit and needs to be accounted for. I'm sure there are many other factors a serious engine tuner would consider as well, but me being a firewood, weekend hack wannabe, I'm sure that opening them up to breathe better is going to make a difference whether it's 50% to 150% ratio. I've always heard the talk, and have felt the increases in my own saws even with my own humble hacking, but just kinda curious what some of the pro's have to say about optimum tuning of just a muffler mod on a factory piston and jug, although I'm sure they don't want to give away all their top secret tuning tips.

Just like with a car back in my day, dropping a set of headers and glass packs in makes a nice difference for me on my daily driver, but showing up at the race track with that as the only mods could be rather embarrasing!!!

As for my chainsaw, I'm just looking for the best I can do with a scrench, pliers, dremel, and drill on a slow Thursday evening while one of my buddies holds my beer and watches... LOL

Speaking of beer, it's gotta be 5:00 somewhere...

 

With those tools you can always make the hole bigger later.....harder to make it smaller. Drill a hole, run a few tanks of fuel through it, and maybe drill another later if it doesn't seem like much changed.

 

Hey Lukem. Could you show a pic of that? I have a 362 cm would like to see that. Thanks