The theory and physics of muffler mods, and their practical effects

[belgian]

Some saws come with a plug with too hot of a heat range. Just because it comes from the store like that doesn't mean thats optimum.

Even if manufacturers can make better parts, its cheaper just to buy parts from some other distributer (Champion, NGK, Autolite) than make the plug themselves. Do you honestly believe that a saw manufacturer is going to pay for the tooling to make their own spark plugs when they can easily just add 1mm to the bore of their saw and call it a day? It doesn't matter how many saws they make. Its always cheaper to outsource a generic part than come up with the tooling to make your own.

It's very common that manufacterers develop a particular component together with an independant subcontractor, and take exclusivity rights for it. if Stihl for ex. were to be seeing advantages in a particular plug design for their saws, it would be relatively easy for them to find a plug maker and agree upon exclusivity, provided that they share development cost or commit to certain sales numbers, and if the design can be protected by a patent.

A lot of people have the "you can't make it better" attitude. A lot of saws have less than optimum porting. Why is that? Ported saws cut faster than a stock saw. Why didn't the factory make the ports the same as in a ported saw? If one manufacturer was really trying to get an edge over another, don't you think they would open up their ports a little? I'll give you a hint. It doesn't have to do with emissions. Saws made before the EPA cracked down can be ported too.

Most people don't care. I'm probably just :deadhorse:. sorry.

don't get defensive. It's OK to think outside the box sometimes, but I agree with Philbert, that if the plug design you promoted is so much better and simple to do, why do plug makers not make them standard like that ? I suspect that your design has indeed some negative effects to it, that make them less universal in use or create some minor risk.
If a modification is proposed like you did, it's quite normal that people start debating it and ask questions. We try to understand.

Same thing for the porting issue. You don't generally produce saws for a niche racing market, but for the entire pro/consumer market. That, along with some emission laws, do force saw makers to sign for a lot of compromises, and results in a product that adresses the needs of the majority of the market.
Folks on this forum has outlined enough what modding can do to a saw, but saw makers think different for obvious reasons.

 

[edisto]

I suspect that your design has indeed some negative effects to it, that make them less universal in use or create some minor risk.

You'll see manufactured side-gapped plugs for 2 strokes in most of the old motorcycle tuning books, including some where the spark moves sideways to the center electrode (strap is level with electrode), which creates some clearance above the piston to prevent local heating.

The idea is an old one (I'm surprised that people are surprised by the suggestion), and theoretically sound, i.e.,amount of edge is more important than electrode area for spark propagation. The disadvantage is that all the wear is on one side of the electrode, so the plugs don't last as long.

The reason we don't see side-gapped plugs now might simply be because the improvement in performance does not justify the retooling that might be needed to produce the plugs, or from a consumer standpoint, does not justify the shorter plug life.

It seems to me that grinding a radius similar to the radius of the center electrode would be an improvement over just cutting the strap flat.

 

[RTK]

It was a bit of a facicious question, soory.

I don't know achieving both is possible in a typical saw with the plug angled in from the rear intake side of the cylinder. The first senario would place the ground strap in a saw to the bottom and gap up, the second would place the ground strap up with gap facing towards the intake/transfer flow.

In general terms it sounds best to have the gap facing the exhaust but then some say the intake. Also it is best that the ground strap does not block the path to the center of the chamber, that puts the ground strap back to the botom. But then in these tight engines placing the ground strap close to the piston can be a problem.

That leave it maybe best to put the electrode to one side or the other. Problem is at most its a 1-2% change. I have yet to see anyone who can put in three back to back timed cuts that don't vary at least that much, so how would this 1-2% change in performance be detected?

.

Correct it would make little difference, but according to my engineer buddies it does a little depending on squish angle etc.
The strap would be neither straight up nor straight down, my answer was a not very descriptive. All depends where the plug is located.

 

[oldsaw]

Yup... funny how so many people think that when both wheels spin in a rearend that it has a "posi" diff in it. Regardless of brand.

To dig even deeper and derail this choo-choo some more...

AMC = Twin Grip

FoMoCo = Traction-Loc

Mopar = Sure Grip

Then we get to GM... Leave it to GM to make it confusing for all brands under their mark...

Chevrolet = Positraction

Cadillac & Olds = Anti Spin

Buick = Positive Traction

Pontiac = Saf-T-Track



Gary

Heeeyyyy maaaaan, I'll just call it LSD, maaaan. Limited Slip Differential.

 

[timberwolf]

All depends where the plug is located.

Xactly!

Cut off head race saw and I have found a couple occasions that favored facing the gap to the exhaust side was an advantage, but the way the plugs are located on a typical saw it's a crap shoot and little way to tell which is best. There is 50 other things to chace first in the quest for cutting speed.

If I get at it might be possible to see a difference on dyno, even there I think it a pretty small change to pick out.

 

[Philbert]

As long as we are talking about spark plugs, does it make a practical difference if I use a resistor or non-resistor plug?

Thanks.

Philbert

 

[Log Hogger]

Sounds like it's worth trying

I'm not really sure as far as gapping the plugs more or less often. I have dyno results from a 2 stroke snowmobile that had the plugs replaced with side gapped plugs. The power curve was slightly higher than a normal plug. I can look for them, but they're in a dark corner of my hard drive. I'll have to look for them.

It does make the saw rev smoother and give a subtle increase in hp.

There are actually plugs made like that for 2 strokes, but they're considerably harder to find at the store than the regular plugs.

They also make a plug that has a little platinum wire. Platinum has a higher melting point than iron, so it can be made into a point. A pointed iron ground will glow red hot and cause dieseling.

Those two prong plugs are a gimmick. Not only do they block the electrode, but you also have to have them gapped exactly the same for them to work. A spark is going to follow the path of least resistance. Unless your grounds are perfect (Which is pretty much impossible) you'll only have a spark on one side and not the other.

Cool, I'll have to give the side-gap plug a try. I'm not surprised that the two prong plugs are a gimmick, if they actually worked, why wouldn't all plugs be made that way? The two prong ground strap is not so original that nobody would have thought of it before!

 

[Philbert]

The two prong ground strap is not so original that nobody would have thought of it before!

Some of the Bosch automotive plugs have 4!

Philbert

 

[nanuk]

R2000 dc4

engines had plugs that have two electrodes that are along side the center post, and are level with it.

that's 100 inches per cylinder.. a lot of fuel to ignite.

 

[treehoe]

has anyone tried a muffler mod on a o20/ms200t?

 

[treehoe]

has anyone tried a muffler mod on a 020/ms200t?

 

[buck06]

I am new to the sight and i like all the good info. I also have a ms390 that is a year old and would like to do a muffler mod on, i could use a little help on what size the hols are and how much the H and L jet are adjusted 1/8, 1/4 ect. i have ran 20 to 30 tanks of gas in her so i beleave she is broke in could use some help please "pics. would be nice" thank you

 

[Gabriel1982]

No, I'm not explaining them. I'm asking about them.

I've been researching this site for a long time and I've found some very useful information. But I still have quite a few unanswered questions. Please bear with me as I take you through my train of thought.

When someone asks: "How does a muffler mod improve performance?", the usual answer is: "It increases air flow. The more easily an engine breaths, the better it runs."

Unfortunately, that begs the question: By what mechanism does air flow increse power?

On the one hand, I've read that the power increase comes from the increases in RPMs resulting from increased air flow. On the other hand, I've read that the H screw needs to be richened in order to keep the saw from over revving.

There's also the matter of greater power output (or is it more specifically, torque?) from a modded muffler at the same RPM level, compared to a non-modded muffler.


While pondering that, let me back up and explain my specific situation.

I have an MS390 which I'm considering modding. For purposes of this discussion, I'm making a rough comparison between it and the MS361. Anyone tempted to get sidetracked with the usual "pro saw versus consumer saw" debate, don't bother. My comparison has specific relevance to this discussion.

The 390 is rated to run at 13,000 RPMs. The 361 runs at 14,000RPMs. Given this difference alone (and an identical bar and chain setup), the 361 will clearly out perform the 390. However, engine speed doesn't tell the whole story. The other part is how well an engine maintains what speed it can muster under load. That's where non-speed related power/torque comes in. The 390 and the 361 have identical strokes, but the 390 has a slightly larger bore, so theoretically it would probably have a little more torque, thus what it lacks in top end speed, it partially makes up for in ability to motor through without bogging at a given speed. By comparison, the 361 generates at least a fair portion of its power through higher RPMs.


It appears that muffler modification can have two effects. One is that it increases power/torque across the RPM range. The other is that it increases actual engine speed, which results in faster cutting. It also appears that the most pronounced performance increase will be realized from a faster running engine, although that runs the risk of overheating and ruining the engine if you don't back out the "H" screw to allow more fuel through.


So here's where I need answers.

Is the purpose of richening the mixture after modding to bring the RPM level back down to spec, does it just provide more fuel to cool down a faster running engine, or does it do both?

Does muffler modding a saw necessarily mean sacrificing engine lifespan?

How much, if any of an RPM increase is "safe"?

Finally, other than the plastic crankcase, how are the actual engine materials between the 390 and 361 any different? I know the rod and bearings are the same. What about the cylinder and crank. Given the identical stroke between the two saws, I'm tempted to initially conclude that at least the cranks are identical.


Again, I don't want to debate the merits of one saw versus the other. I really just want to know how a proper muffler mod should be approched in principle. My comparison was to illustrate what I perceive to be two slightly variant approches to developing horse power.


If anyone has answers, I'll be most appreciative.

Very good topic. I myself am "itching" to mod SOMETHING on makita 6100 I used it many times until now ,but today I removed the muffler and am studying it closely... Did I read right "plastic crankcase"?! I wouldn't buy anything plastic... Related to wood cutting!

 

[link]

Very good topic. I myself am "itching" to mod SOMETHING on makita 6100 I used it many times until now ,but today I removed the muffler and am studying it closely... Did I read right "plastic crankcase"?! I wouldn't buy anything plastic... Related to wood cutting!
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Makita 60cc (Dolmar) is one of the best saws ever made.
Dont do excess, a little goes a long way.

 

[turkeybob]

Very good topic. I myself am "itching" to mod SOMETHING on makita 6100 I used it many times until now ,but today I removed the muffler and am studying it closely... Did I read right "plastic crankcase"?! I wouldn't buy anything plastic... Related to wood cutting!
View attachment 998252View attachment 998253

 

[turkeybob]

The rule of thumb is normally 80% of exhaust outlet size. The 6100 is not far off and exhaust is quite free flowing standard. Mine feels pretty zippy without mods, just keep spark arrester clear, periodically heat it up with a blow torch to clear carbon. I have a property in Romania with a forest and use my 6100, and 115i , I have a 7900 and 120si in the UK but find the 6100 does for me in Romania and because of the 10% ethanol crappy fuel I am looking for a supplier of Aspen in Romania, either near to Buzau(my brother in law has a business close to there) or near to my house in Hunedoara county, do you know a supplier Gabriel1982? Just got back today from three weeks over there, very hot and no rain for weeks!

 

[Gabriel1982]

The rule of thumb is normally 80% of exhaust outlet size. The 6100 is not far off and exhaust is quite free flowing standard. Mine feels pretty zippy without mods, just keep spark arrester clear, periodically heat it up with a blow torch to clear carbon. I have a property in Romania with a forest and use my 6100, and 115i , I have a 7900 and 120si in the UK but find the 6100 does for me in Romania and because of the 10% ethanol crappy fuel I am looking for a supplier of Aspen in Romania, either near to Buzau(my brother in law has a business close to there) or near to my house in Hunedoara county, do you know a supplier Gabriel1982? Just got back today from three weeks over there, very hot and no rain for weeks!

Aspen fuel supplier? Don't know of any. I just buy the best/most expensive gasoline from Petrom gas station and mix 1 liter with 30ml of Motul off road 2 stroke synthetic oil. So far worked well. Only problem I had was with Lukoil gasoline I bought in a hurry beeing too far from any Petrom gas station. The 6100 with that fuel and same 30ml motul oil stalled while in the log of 50-60 cm diameter just after finnishing the cut. I was shocked it happened... But it was 36-37 celsius heat in shade while I was in the sun whole day... Second day I used Petrom most high octane fuel with 30ml of Motul and it never did stalled once... Same 35 degree celsius heat and sun... Guess Lukoil has bad gas too,besides beeing russian owned...
I never used Aspen fuel!