Chainsaw Pipe Exhaust theory

[paragonbuilder]

Being a science nerd, I did some calculations.......

Assume 7.5cm from the muffler opening to the muffler cover. Times this by 2, gives you 0.15 in metres. Divide by the speed of sound in m/s (that being 343). This tells me that the reflected pulse will take

0.15 / 343 = 0.00044 seconds to reach the muffler opening, after rebounding from the muffler cover.

Then consider a 2 stroke revving at 10000 rpm, (or wherever you are for peak torque under load). Divide by 60, gives you 167 revs/second, invert that value, and you have 0.006 seconds for a single rotation.

Since (0.0004/0.006 * 360) = 24 degrees of rotation.

(therefore at 10K, the crank has rotated ~24 degrees in the time taken for the pulse to reflect in the above example)

Feel free to flame me (I guessed one or 2 figures and rounded up or down in places), but this says to me that the timing of a reflected pulse at saw operating saws probably has some consequence. I can go through the maths in more depth if required.

It may have some consequences, but there is no way to tune a muffler can for a saw. The pulse would be way to fast as your math shows, if it is correct. The pulse needs to be right before exhaust closes and at the desired rpm or it is either hurting the saw or doing nothing.


Sent from my iPhone using Tapatalk

 

[MattG]

It may have some consequences, but there is no way to tune a muffler can for a saw. The pulse would be way to fast as your math shows, if it is correct. The pulse needs to be right before exhaust closes and at the desired rpm or it is either hurting the saw or doing nothing.


Sent from my iPhone using Tapatalk

I'm kinda just playing with the maths out of my own curiosity to be frank. But before I did so I didn't realise that the delay of the pulse (0.00044) was actually a reasonable fraction of the time period of a rotation at 10k.

 

[MattG]

The deal with the pulses around the opening is not hard and fast......essentially at varying revs we are comprising purging efficiency (which will prefer a negative pressure) over charge compression (which will prefer a positive pressure).

 

[bikemike]

Some aftermarket moped performance pipes are a good start to a pipe for a saw.
I have 1 on my 49cc echo and it makes great power and a broud range of power and chit tons of torque. I have no regrets from a pretty strong saw to a lot more saw than it was. I like it

 

[bikemike]

I didn't do much math vs fitment on 2 saws I piped. But I got luck and think the style of header tube and length of it plays a big role in how and where it makes its power and tourqe

 

[bikemike]

Hi Folks.

I have been doing a bit of thinking about piped saws and am wondering if some folks with a bit of knowledge on them and the theory's behind how they help make power could add some food for thought?

Also, are they generally custom made or can they be bought from anywhere for popular saw models?

moped pipe on the echo. Parts together a pipe for the Poulan

 

[Czed]

@GD350TURBO
here's some pipe info

 

[Lightning Performance]

View attachment 69412 moped pipe on the echo. Parts together a pipe for the Poulan

Do the math and see how those pipes stack up.

 

[Chainsaw Jim]

I'm curious how this pipe would compare to a pipe calculated and built specifically for this saw.

The smoke coming up is from a pinhole in the flange weld.

 

[Tomos770]

I didn't do much math vs fitment on 2 saws I piped. But I got luck and think the style of header tube and length of it plays a big role in how and where it makes its power and tourqe

 

[Tomos770]

Some aftermarket moped performance pipes are a good start to a pipe for a saw.
I have 1 on my 49cc echo and it makes great power and a broud range of power and chit tons of torque. I have no regrets from a pretty strong saw to a lot more saw than it was. I like it

Most Scooter pipes are built for 70ccm cylinder kits.....some are for 50ccm

 

[Tomos770]

Interesting idea...