Chainsaw Pipe Exhaust theory

[edisto]

General theory question that might apply to “dog dick” style pipes:

If the ideal distance of an expansion pipe is 40cm, can a 20cm pipe utilize the sound wave on its secondary reflected pulse? What about 10cm?

Both waves (the initial negative and subsequent positive) have to occur during one exhaust port open cycle to be beneficial.

Related question:

What negative effects does the sound wave have if it hits the exhaust port too early in the cycle?

The initial negative wave pulls charge into the exhaust (helps scavenging), and the subsequent positive wave stuffs some of that charge back into the cylinder (supercharging). Early arrival of the positive wave would interfere with scavenging.

 

[Fabulous]

Just so you know...the long pipe is the first step in an expansion chamber. The pulse leaving the opening reflects a negative pressure wave that helps with scavenging. A straight pipe works at only a narrow range of rpms. A cone reduces the strength of the pulse, but spreads it over a wider range of rpms.

Having seen the length of the pipe required, it should be obvious to you that the "dog dicks" are not tuned pipes.

Not “tuned” as in an expansion chamber however anything you do to get the exhaust out (“can’t get in if it can’t get out”) quicker is going to increase performance. If one were to “pipe” a stock muffler one could make the argument that the torque curve (and thus hp) will vary depending on the size / length / number of the outlet tube(s) and numbers of tubes. It’s common knowledge that a 3/4 inch tube placed “x” distance into the muffler will give enhanced performance on an “x” cc saw. In fact , hay chaff and sawdust has uploaded several videos where he shows , plain as day, this effect … and yes , he has a Dyno to show “real world results”. I suggest perusing his collection - you might just learn something! As for me, saws are tested in the wood and I can unequivocally say that a “dog dick” muffler will outperform any stock can everyday of the week and twice on Sunday

 

[Fabulous]

 

[jacktheripper]

What also sucks about dog dicks is that they are super loud. They just won’t shut up.

 

[edisto]

Not “tuned” as in an expansion chamber however anything you do to get the exhaust out (“can’t get in if it can’t get out”) quicker is going to increase performance.

Like a simple widening of the outlet?

It’s common knowledge that a 3/4 inch tube placed “x” distance into the muffler will give enhanced performance on an “x” cc saw.

3/4" seems oddly specific. How did you arrive that number? Or are you just parroting the YouTube? Can you solve for x?

What is common knowledge is that opening up the outlet of a box muffler improves performance. At some point the loss of back-pressure will negatively affect performance, but modern muffler designs attempt to keep charge out of the exhaust, sacrificing performance for emissions.

I suggest perusing his collection - you might just learn something!

You have been perusing his collection a lot, and seem to have come away with very little.

Check out his video where he compares modifications to box mufflers on a Holzfforma G366:



Orange is stock, green is his modification, and the others were modified mufflers sent to him:


Now, compare those gains to the gain from his magical "Ironhorse" on a Husky 455 (pay attention to the scale on the Y-axis):




3 hp to 3.4 hp with the iron horse (13%), similar to the single opening mods on the box mufflers, and less than the double-opening mod by a lot.

No-one is saying that a "dog dick" wouldn't outperform a stock muffler, just that you could get similar results in a fraction of the time with a stock muffler and a step drill bit.

 

[Fabulous]

What also sucks about dog dicks is that they are super loud. They just won’t shut up.

Unfortunately they ARE considerably louder than a stock muffler or a stock muffler with another outlet affixed but that’s the price you have to pay for increased performance