True benefits of a muffler mod

[blsnelling]

Brad on the 7900 were you just opeing up the outlet or adding a second hole without opening the muffler up to dejunk it? On 675 and 681 solo I found gains in the muffler, given it is nearly identical design to the 7900 I would think there should be some gains to be had on the 7900.

I opened up the muffer through the inlet, and then added a second port. You testing seems to be more accurate than mine What kind of gains did you come up with?

 

[woodyman]

For starters if you don't want to hack on your muffler, pull the spark screen out and see if it makes a difference.

I don't mind hacking on mufflers alittle

 

[fearofpavement]

To disparage the engineers of mechanical equipment because it can be easily modified to "work better" shows ignorance of the constraints that they operate under. Most engineers are pretty smart guys and are fully aware they could get more power or performance out of the products they design if they could do it how they wanted. However, the world is full of people that make laws regarding a myriad of issues. Just for chainsaws think of all the limitations: kickback minimization, noise limits, pollution/emission limits, oxygenated unleaded fuels, bar oil dispersal rates, market price points, and so forth and so on. Thus, some aftermarket mods often serve to remove the restrained performance. Sites like this help others to know how best to get back what could have been there in the first place if not for Washington red tape.

 

[ShoerFast]

To disparage the engineers of mechanical equipment because it can be easily modified to "work better" shows ignorance of the constraints that they operate under. Most engineers are pretty smart guys and are fully aware they could get more power or performance out of the products they design if they could do it how they wanted. However, the world is full of people that make laws regarding a myriad of issues. Just for chainsaws think of all the limitations: kickback minimization, noise limits, pollution/emission limits, oxygenated unleaded fuels, bar oil dispersal rates, market price points, and so forth and so on. Thus, some aftermarket mods often serve to remove the restrained performance. Sites like this help others to know how best to get back what could have been there in the first place if not for Washington red tape.

Thank you!

Nothing like hitting the nail on the head.

It's a fact that the muffler restriction is the favorite place for the manufacture to limit 'outputs' , it's extremely cost effective.

It is also very easy for the end user to open up, or have the restriction opened up.

Tieing this into the OP, the only way a currant hand-held engine will not make more power with the exhaust opened up, is if the engine was tuned on the lean side before the mod. Opening the muffler requires a richer 'H' setting, a saw already slightly lean will trip all over it's self after the flow is 'un'-restricted.

 

[timberwolf]

As far as gains on a 660, The 026/260,036,046/460 and 066/660 share so much of the design it is almost as if the engines are simply just scaled up or down in size. Muffler gains seam to also be in that 20% range. With the excption of some of the ones that had larger muffler openings to start, like the 066 with DP front cover ect.

As far as the solo/dolmars not as much gain but still a good 10-15% Saws with rev limited coild can make it a bit harder to decide just what the gains are as tuning becomes a bit more of wildcard and is not as repeatable as tuning by tach.

 

[Ambull]

I have never really understood two stroke expansion chambers in an exhaust, but they are a bit more complicated than a four stroke. I come from a hot rod automotive background. I went to the PA GTG last weekend, and have now been bit by the hot rod saw bug, lol.

Because of this, I am trying to gain an understanding for how a two stroke exhaust works. Here is something I found on the internet that I thought I could share with you:

http://www.motorcycle.com/how-to/ho...ambers-work-and-why-you-should-care-3423.html

Anyways, it is clear that simply opening up a two stroke exhaust, or "drilling holes" as someone wrote, may not necessarily give you gains. The expansion pipe effect is essential in getting the most out of your two stroke.

 

[Trigger-Time]

I have never really understood two stroke expansion chambers in an exhaust, but they are a bit more complicated than a four stroke. I come from a hot rod automotive background. I went to the PA GTG last weekend, and have now been bit by the hot rod saw bug, lol.

Because of this, I am trying to gain an understanding for how a two stroke exhaust works. Here is something I found on the internet that I thought I could share with you:

http://www.motorcycle.com/how-to/ho...ambers-work-and-why-you-should-care-3423.html

Anyways, it is clear that simply opening up a two stroke exhaust, or "drilling holes" as someone wrote, may not necessarily give you gains. The expansion pipe effect is essential in getting the most out of your two stroke.

I don't know enough to even speak on this, but for most of use pipes are no good.

OSHA a few years ago said our saws were to loud and to protect us.
They made manufacture make them quieter. So the saw co. made the exhaust
opening smaller choking our saws down. People like me just open port
back to pre OSHA days.

Stihl even quieten down the air intake in 066 to get the sound level down.

Lot of people think it was EPA, what we a seeing with the new saws is EPA
and them SOB's are just getting warmed up!!


TT

 

[RTK]

The EPA is no manufacturers friend, that is for sure. I recently ran a saw with a cat. Holy cow, you could light your cigarette off of that thing.

 

[brages]

Anyways, it is clear that simply opening up a two stroke exhaust, or "drilling holes" as someone wrote, may not necessarily give you gains. The expansion pipe effect is essential in getting the most out of your two stroke.

I'll let the experts correct me, but if you're dealing with the typical 3" or so depth of a chainsaw muffler, there can be no meaningful expansion chamber effect -- i.e. timed waves of pressure & rarification coinciding with the needs of the engine.

 

[gemniii]

To disparage the engineers of mechanical equipment because it can be easily modified to "work better" shows ignorance of the constraints <snip>

In my readings here I have not found much "disparaging" of the engineers of the major brand chainsaws, especially Stihl. And I sincerely hope they don't think we are disparaging them. Unlike I disparage the engineers who made the diesel GM cars in the '80's, the Ford successors to the 7.3, the Corvair.

Three things affect me and my 660's:
1. To make the engine quieter they decreased the hole in the muffler. They could have made the engine smaller. Easily overcome with a bigger hole or a DP cover or both.
2. To lessen the oil use for EPA they turned down the oiler pump. Easy mod to overcome.
3. To make sure you comply with all the laws they put limiter caps on the carb adjustment screws. These make it impossible to really tune the saw, unless you can obtain a deck screw (vastly expensive, almost 10 cents each).

I've taken a $1,000 saw and improved the performance by 20% for the cost of a DP muffler cover and a deck screw. My neighbors will have to suffer another couple of hours of loud noise and I'll probably use more fuel. My high performance oilers will probably put another quart of oil into the environment (not quite up to BP standards).

So rather I praise the engineers. They come up with an 8hp saw being sold as a 7hp saw to meet some regulations. And they basically put in warnings saying "don't do this unless you want more power and are willing to put up with noise and increased fuel consumption".

Now for businesses that have to meet noise and pollution guidelines, well they'll just have to buy 880's.

 

[Ambull]

I'll let the experts correct me, but if you're dealing with the typical 3" or so depth of a chainsaw muffler, there can be no meaningful expansion chamber effect -- i.e. timed waves of pressure & rarification coinciding with the needs of the engine.

I am no expert by any means, but I will correct you. I took the cover off the muffler on my Dolmar 5105, and you can clearly see the expansion chamber.

It's there.

 

[RTK]

That is not an expansion chamber in the sense of a tuned exhaust. That is what is above of the cat (restriction).
Tuning would have too take place before that too be of any affect/benefit.
I believe they made that area to light your cigarettes off of

I'll let the experts correct me, but if you're dealing with the typical 3" or so depth of a chainsaw muffler, there can be no meaningful expansion chamber effect -- i.e. timed waves of pressure & rarification coinciding with the needs of the engine.

Yep, it is pretty tough to get a piped affect with the size of stock mufflers.

 

[Justsaws]

To disparage the engineers of mechanical equipment because it can be easily modified to "work better" shows ignorance of the constraints that they operate under. Most engineers are pretty smart guys and are fully aware they could get more power or performance out of the products they design if they could do it how they wanted. However, the world is full of people that make laws regarding a myriad of issues. Just for chainsaws think of all the limitations: kickback minimization, noise limits, pollution/emission limits, oxygenated unleaded fuels, bar oil dispersal rates, market price points, and so forth and so on. Thus, some aftermarket mods often serve to remove the restrained performance. Sites like this help others to know how best to get back what could have been there in the first place if not for Washington red tape.

Engineers are a cog in the wheel.

Some companies look at the regs they have to comply with and that they will have to comply with and then set out a business plan to so with some completely engineered new products.

Some companies apply strap-ons to antiques and call it good enough. At least they did not mount a smog pump to their saws yet.

Maybe the best thing to do would to have these companies purchase other companies that have some engineering and design abilities to design them some modern saws that comply with the exsisting regs or at least make them buy a freaking bridge.

 

[RTK]

or at least make them buy a freaking bridge.

That would probably be the easiest given politicians

 

[ShoerFast]

That is not an expansion chamber in the sense of a tuned exhaust. That is what is above of the cat (restriction).
Tuning would have too take place before that too be of any affect/benefit.
I believe they made that area to light your cigarettes off of




Yep, it is pretty tough to get a piped affect with the size of stock mufflers.

Yes, that is a 'divergent duct' , used to decrease the velocity and increase the pressure of the exhaust for a longer/stronger burn in the cat.

This is more of a tuned exhaust 'piped'.

 

[RTK]

Exactly, but there is no way it is going to have any affect like a pipe except on the cat, maybe that is the reason they double as cigarette lighters.
I run pipes on engines from 30cc to 116cc in a different application.
I really like the way a piped engine runs for my situation, snappy response, power etc. My rpm range is much lower than these saws, around 7000 give or take max and usually between 3500 to 7000rpm running rpm. Pipe lengths and headers are much longer than those for saws d/t the lower rpm.

Perfect animation on the functioning of a pipe.


.

 

[timberwolf]

361 Shootout

Have 2 361s and a 361BB on hand so thinking of comparing a muffler mods along this line and also the BB vs factory cylinder and piston.

Hope to get some dyno and flow bench numbers as well.

Edit(oops ment to put it in a new thread)

 

[Ambull]

Yes, that is a 'divergent duct' , used to decrease the velocity and increase the pressure of the exhaust for a longer/stronger burn in the cat.

This is more of a tuned exhaust 'piped'.

Thanks for the help. As I said I am no expert. I still think that this muffler has been engineered to maximize the horsepower while minimizing sound levels. I am sure that if I drilled a hole in the center of the chamber, it would just make it louder.

I think I may take the cat out of this thing though. It is pretty easy to get at through the other end, and if I am careful with a drill bit and chisel I should be able to bust it right out of there.