Exhaust scavenging - ZR-1 Net Registry Forums

Paul Workman · 01-28-2020

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 · 01-28-2020

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 · 01-30-2020

Quote:

Originally Posted by 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

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 · 01-31-2020

Quote:

Originally Posted by Paul Workman

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 · 01-31-2020

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 · 01-31-2020

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

01-28-2020	#1
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Exhaust scavenging 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 __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry

01-28-2020	#2
Karl Join Date: May 2013 Location: Chicago Posts: 977	Re: Exhaust scavenging 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 __________________ 1993 ZR-1 #211 Yellow On Beige Beast #2 1992 ZR-1 #427 Black On Black Sold 1985 L98 Blue On Blue Sold

01-31-2020	#5
32valvZ Join Date: Nov 2007 Location: Sunshine State Posts: 1,071	Re: Exhaust scavenging 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. __________________ [B]1990 #2815[/B] [COLOR="Red"][B]Red/Red[/B][/COLOR] Ported Plenum & IH (by Pete) Haibeck Chip Rebuilt FPR (by Phil) FIC Injectors Watson LT Headers 3" Stainless Works exhaust Lingenfelter Open Air Lid Bill B Built Transmission Shifter & C Beam Plates [FONT=Impact][COLOR=red]1992 [COLOR=black]#[/COLOR] 091[/COLOR][/FONT] [FONT=Impact][COLOR=#ff0000]Red/[COLOR=silver]Gray[/COLOR][/COLOR][/FONT] [B]SOLD[/B]

01-31-2020	#6
Karl Join Date: May 2013 Location: Chicago Posts: 977	Re: Exhaust scavenging 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 __________________ 1993 ZR-1 #211 Yellow On Beige Beast #2 1992 ZR-1 #427 Black On Black Sold 1985 L98 Blue On Blue Sold