Exhaust scavenging

[Paul Workman]

For we frustrated mech engineers, I ran across this Youtube explanation of the intricacies and engineering in designing the exhaust system. Good stuff!

And, incidentally, much of the same physics (pressure waves caused by inversion when runner diameters suddenly change - either bigger or smaller) applies to induction design, since we all seem to be interested in porting that enhances the LT5 so well. Enjoy!

https://www.youtube.com/watch?v=jjPeP_Nn2B4

[Karl]

Here are a few videos with hands on information vs talking to the chalk board for 9 minutes!

https://www.youtube.com/watch?v=NekTRPx68zs

https://www.youtube.com/watch?v=O1bXPNy1Yn4

https://www.youtube.com/watch?v=_PVXvHkr-Vs

[Paul Workman]

Here are a few videos with hands on information vs talking to the chalk board for 9 minutes!

https://www.youtube.com/watch?v=NekTRPx68zs

https://www.youtube.com/watch?v=O1bXPNy1Yn4

https://www.youtube.com/watch?v=_PVXvHkr-Vs

Thanks Karl! Now, the next piece to add would be the theory and a video on the affects of reversion due to sudden changes in runner diameter i.e., applicable to BOTH induction and exhaust systems.

Oh, and I think the old saw about "back pressure" is pretty well dispelled too.


All good "bookmarks" for future reference! Now for a reversion piece and then maybe a piece on angle vs. straight(er) runners, to flesh this thread out.

[Karl]

Thanks Karl! Now, the next piece to add would be the theory and a video on the affects of reversion due to sudden changes in runner diameter i.e., applicable to BOTH induction and exhaust systems.

That sounds like a topic for an advanced automotive degree program!

[32valvZ]

Written by: Steve Hendren from Hendren Racing Engines

Since the public introduction of our anti-reversion muffler by crateinsider.com, I’ve received multiple questions about these mufflers each week. So, I’ve decided to sit down and try to explain the benefits of reducing exhaust reversion.

Without getting too technical, which I’m not very technical anyway, we must first understand what exhaust reversion is, and secondly, how it affects an engine. Reversion is simply the flow of exhaust gasses back into the combustion chamber when the downward movement of the piston creates a vacuum in the cylinder. This event occurs when the camshaft is on the overlap, i.e. the exhaust valve is still open as the intake stroke begins. Now begin to think about the spent gasses that just left the combustion chamber, traveling out of your header pipe, approaching the collector and exiting directly from the collector or extension in the form of a pressure wave. When this pressure wave reaches the end of the pipe, it will be reflected in the form of a pulse. Simply put your hand over the end of your collector with the engine running, and you can feel these pulses. Some of this reflected pressure wave in the form of a pulse is then drawn back into the header thanks to camshaft overlap. This occurs, again, as both the exhaust and intake valve are open and the piston is moving back down the cylinder. The movement of the piston back down the cylinder, coupled with the opening of the intake valve as the exhaust valve is still open, creates an instantaneous vacuum that pulls air from the pressure wave/pulse back into the cylinder. Any exhaust gases that are drawn into the combustion chamber will displace the air/fuel mixture being drawn in through the intakes valves, contaminating the charge in the combustion chamber, thus reducing the volumetric efficiency of the engine, as well as engine power/torque. The more overlap that is built into a camshaft, the more reversion the engine sees. In extreme cases, you will also see residue from exhaust gasses in the plenum of intake manifolds. This is quite common on street engines with big radical camshafts that “beat the earth,” as people here in the south like to say.

[Karl]

Looks like you can purchase an anti reversion chamber and insert it in your header collector.

https://youtu.be/HNeY_Vge5gs

Has anyone used one?

For the diy people you can make your own also.

https://youtu.be/t2L94tgydNo