Chainsaw Pipe Exhaust theory

[Ketchup]

Does anyone have credible information about the speed of exhaust gas when it leaves the chamber, how quickly it decelerates as it moves into a larger, cooler space and how much it expands?

I’m sure it’s out there, but asking is a lot faster.

 

[bwalker]

Well said.
But I don’t want to completely discount a muffler design just because idiots like it. I think there’s something to a flat wall across from the exhaust port and to reduced muffler volume. Even idiots have happy accidents or get something partially right.

I think increased muffler volume is beneficial, but it's not a hill i would die on.

 

[bwalker]

Does anyone have credible information about the speed of exhaust gas when it leaves the chamber, how quickly it decelerates as it moves into a larger, cooler space and how much it expands?

I’m sure it’s out there, but asking is a lot faster.

Thats a factor in pipe design. I believe there is open source pipe design programs out there.

 

[edisto]

Does anyone have credible information about the speed of exhaust gas when it leaves the chamber, how quickly it decelerates as it moves into a larger, cooler space and how much it expands?

I’m sure it’s out there, but asking is a lot faster.

Jennings talks about wave speed, but not about exhaust speed...although they have to be related. I attached a pdf of his book so you can see the chapter on expansion chambers.

The exhaust temps drop when they enter the expansion chamber, but recover most of that loss when they get compressed at the back cone. Jennings estimates 1200 F at the port, dropping to 500 F in the chamber, and getting pushed back up to about 800 F by the rear cone.

I'm not sure that it will work, but I found an electronic copy of Jenning's book and attached it here. I'll see what Bell says about it in his book later tonight.

 

[bwalker]

Jennings talks about wave speed, but not about exhaust speed...although they have to be related. I attached a pdf of his book so you can see the chapter on expansion chambers.

The exhaust temps drop when they enter the expansion chamber, but recover most of that loss when they get compressed at the back cone. Jennings estimates 1200 F at the port, dropping to 500 F in the chamber, and getting pushed back up to about 800 F by the rear cone.

I'm not sure that it will work, but I found an electronic copy of Jenning's book and attached it here. I'll see what Bell says about it in his book later tonight.

Don't forget that stinger diameter greatly influences pipe temps.

 

[edisto]

Don't forget that stinger diameter greatly influences pipe temps.

It is definitely is worth repeating as often as possible, because it can influence them in a very bad way if the diameter is too small, or the length too great.

 

[bwalker]

It is definitely is worth repeating as often as possible, because it can influence them in a very bad way if the diameter is too small, or the length too great.

Yes, very much so. Burndown city. MX bikes have this problem often. Certain pipes are set up for things like Supercross where the time your on the throttle is fairly short. They use tight stingers to aid with throttle response and make the motor punchy. It works. The problem comes about when jo blow buys one and proceeds to take it to the dunes where your into the throttle for long periods of time. Better jet rich and run high octane leaded fuel or you will burn it down via detonation and spectacularly so.

 

[huskihl]

Pretty good discussion in here about actual tuned pipes now

 

[Cyrille72FR]

Jennings talks about wave speed, but not about exhaust speed...although they have to be related. I attached a pdf of his book

That's a lovely book to read.

The exhaust temps drop when they enter the expansion chamber, but recover most of that loss when they get compressed at the back cone. Jennings estimates 1200 F at the port, dropping to 500 F in the chamber, and getting pushed back up to about 800 F by the rear cone.

I read in some french lecture that it translate to 1100m/s at exhaust, cooling down around 500m/s in the chamber.