Any downsides to anti reversion mufflers/devices?

General engine tech -- Drag Racing to Circle Track

Moderator: Team

User avatar
exhausted
Guru
Guru
Posts: 1261
Joined: Mon Oct 29, 2007 9:07 am
Location: Matthews, NC

Re: Any downsides to anti reversion mufflers/devices?

Post by exhausted »

AR devices act as diodes in a given system of pressure waves. If one could assign a percentage number to it's ability to reduce the "power" of pressure waves going through the device, (which we can't) but lets say 20%. Well that is significant isn't it? If you can reduce the amplitude (not the number) of pressure waves going through the system in the wrong direction you should be able to measure it and you can. You can also double them up, keep going larger, (if you have room) and reduce them even more.

Notice they usually do not hurt top end power. (this is mostly because most systems are larger than they need to be. example the "crushed" tubes on the SB header video everyone has seen).

Another point here is that very little if any work has been done on how they are designed and what might work better than another. Just because Hendrin used commonly available muffler components does not mean that it is the most effective way of introducing pressure wave diodes into a given system. I have put them in primaries, secondaries, tailpipes at the begining and the end...results are usually classified.

I am not aware of anyone looking at the ability to run more valve timing in response to more reversion control, but hey that was the first thing the cup guys did when they saw a421 headers. :D
I have done some playing around and the possibilities are scary big for this retired (almost) header guy.
Calvin Elston
Elston Exhaust
Matthews, NC 28104
346-704-4430
Blog: www.exhausting101.com
RevTheory
Guru
Guru
Posts: 5646
Joined: Thu Sep 04, 2014 6:45 am
Location:

Re: Any downsides to anti reversion mufflers/devices?

Post by RevTheory »

exhausted wrote: Fri Dec 17, 2021 8:15 amSnipped...

I am not aware of anyone looking at the ability to run more valve timing in response to more reversion control, but hey that was the first thing the cup guys did when they saw a421 headers. :D
I have done some playing around and the possibilities are scary big for this retired (almost) header guy.
That is exactly what I'm looking into. A/R in the exhaust and on the intake valve. Not to run more rpm but to run the area I need without the ill effects of it in a street application.
Bill Chase
HotPass
HotPass
Posts: 446
Joined: Tue Aug 27, 2019 1:11 pm
Location: Michigan

Re: Any downsides to anti reversion mufflers/devices?

Post by Bill Chase »

SchmidtMotorWorks wrote: Sun Dec 12, 2021 11:51 pm
F-BIRD'88 wrote: Sun Dec 12, 2021 8:10 pm
SchmidtMotorWorks wrote: Sun Dec 12, 2021 1:46 pm Does anyone know of any examples of highly developed performance engines that have these devices?

Motorcycles?
Exotic cars?
These engines don't tune or run at a low enough rpm to benefit..
IMHO anti reversion chambers will work best at relative low rpm and relative restricted inlet applications.
eg: 2bbl dirt oval engines.
Anything where running better at part throttle matters.
Especially if cammed with a tight LSA cam.
Eg: oval track. Anything where a wider powerband with added low rpm torque is better (auto trans, limited #of gears, limited torque converter stall choice), and WOT carb capacity (cfm) is limited.
Typical cammed up street/strip engines.
Has the mechanism by which these work been determined or is this just speculation?

I am not aware of evidence that they actually change reversion.
Exhausted aka Calvin Elston and others have used them successfully to fill torque holes at low rpm, with no significant loss of power up top. Believe he helped a couple road race teams merge collector, ar cans, and tri y headers and had very favorable results.

Pure speculation on my part here, but it seems oems do use the principal idea just they do so with cat-con designs, and layout. I would love to read more verified test data too. Seems those in the know are tight lipped about it.
RCJ
Expert
Expert
Posts: 802
Joined: Wed Jul 25, 2007 6:15 am
Location: Oklahoma

Re: Any downsides to anti reversion mufflers/devices?

Post by RCJ »

I've been working on an oddball project ( anything that is not a sbc) that shows more peak with a tuned open header,but more power everywhere else with short header with an a/r device on the end. It is making me ask the question what is the best shape of an a/r device. Getting on the flow bench and trying different shapes is on the to do list
.
408swinger
HotPass
HotPass
Posts: 104
Joined: Mon Dec 11, 2017 2:16 pm
Location: Boise

Re: Any downsides to anti reversion mufflers/devices?

Post by 408swinger »

SchmidtMotorWorks wrote: Tue Dec 14, 2021 11:12 pm
408swinger wrote: Tue Dec 14, 2021 10:15 am Ktm and Husky 450s. Possibly others but I ride a 2-Stroke and don't keep up on all the new model 4-Strokes . Actually I spend more time researching old Maicos like my 490 Alpha 1.
I can tell you I see those power bulges on most 4-Strokes I see on the track or trail.
Brief search indicates that it is a resonance chamber, didn't find anything about anti reversion.
In fact if it is a resonator, chances are that it actually returns beneficial reversion like a 2-stroke pipe does.
That is entrirely possible. I assumed they were AR devices and have never cut one open to find out.
I can tell you that the exhaust pulses on those big 4-strokes are strong enough to blow your hair around if you are 20 ft behind them ...lol
pcnsd
HotPass
HotPass
Posts: 677
Joined: Thu Dec 13, 2012 12:04 am
Location: North County San Diego CA

Re: Any downsides to anti reversion mufflers/devices?

Post by pcnsd »

RCJ wrote: Sat Dec 18, 2021 8:13 am I've been working on an oddball project ( anything that is not a sbc) that shows more peak with a tuned open header,but more power everywhere else with short header with an a/r device on the end. It is making me ask the question what is the best shape of an a/r device. Getting on the flow bench and trying different shapes is on the to do list
.
I think you are assuming reverse airflow through the device can be extrapolated to pressure pulses. I'm not convinced that is the case. Does the device clip the wave in proportion to area or airflow reduction. Are they one and the same?
20190414_091045.jpg
20190414_091003.jpg
You do not have the required permissions to view the files attached to this post.
- Paul
SchmidtMotorWorks
Vendor
Posts: 11003
Joined: Mon Apr 11, 2005 2:30 am
Location: CA

Re: Any downsides to anti reversion mufflers/devices?

Post by SchmidtMotorWorks »

pcnsd wrote: Sat Dec 18, 2021 10:28 am
RCJ wrote: Sat Dec 18, 2021 8:13 am I've been working on an oddball project ( anything that is not a sbc) that shows more peak with a tuned open header,but more power everywhere else with short header with an a/r device on the end. It is making me ask the question what is the best shape of an a/r device. Getting on the flow bench and trying different shapes is on the to do list
.
I think you are assuming reverse airflow through the device can be extrapolated to pressure pulses. I'm not convinced that is the case. Does the device clip the wave in proportion to area or airflow reduction. Are they one and the same?

20190414_091045.jpg
20190414_091003.jpg
Put it on a flow bench and see.

I'll speculate on the outcome.

1. It will flow less in both directions than a plain pipe of the same size.
2. The flow in each direction will differ slightly, might even be the opposite of what you expect as diverging flow can cause more drag than converging flow.
Helping to Deliver the Promise of Flying Cars
F-BIRD'88
Guru
Guru
Posts: 9802
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Any downsides to anti reversion mufflers/devices?

Post by F-BIRD'88 »

A typical stamped sheet metal Catalytic converter case may be a better "chamber" part of the A/R device.
You could make it "bolt together" capable as a prototype to test various design changes inside.
Straight pipe, cone pipe, pipe diameter, how far extended into the chamber, a venturi on entry pipe or on exit pipe, etc.. etc. Spend your effort on does it work, and what works best on your combo. VS theories.
Sort of like trying out various design types and height(s) carb spacers. Does it work is more important than how it works.
SchmidtMotorWorks
Vendor
Posts: 11003
Joined: Mon Apr 11, 2005 2:30 am
Location: CA

Re: Any downsides to anti reversion mufflers/devices?

Post by SchmidtMotorWorks »

F-BIRD'88 wrote: Sat Dec 18, 2021 11:59 am Sort of like trying out various design types and height(s) carb spacers. Does it work is more important than how it works.
Not to me, if you want to optimise something, the first thing to do is understand how it works.
Helping to Deliver the Promise of Flying Cars
SchmidtMotorWorks
Vendor
Posts: 11003
Joined: Mon Apr 11, 2005 2:30 am
Location: CA

Re: Any downsides to anti reversion mufflers/devices?

Post by SchmidtMotorWorks »

I just ran a quick CFD test forward and reverse.

Forward flows about 3% more.

If it does anything significant, it is as a chamber.
Knowing that, now one can go about optimizing the chamber.
forward_arrows.PNG
reverse_arrows.PNG
You do not have the required permissions to view the files attached to this post.
Helping to Deliver the Promise of Flying Cars
pcnsd
HotPass
HotPass
Posts: 677
Joined: Thu Dec 13, 2012 12:04 am
Location: North County San Diego CA

Re: Any downsides to anti reversion mufflers/devices?

Post by pcnsd »

SchmidtMotorWorks wrote: Sat Dec 18, 2021 11:20 am
pcnsd wrote: Sat Dec 18, 2021 10:28 am
RCJ wrote: Sat Dec 18, 2021 8:13 am I've been working on an oddball project ( anything that is not a sbc) that shows more peak with a tuned open header,but more power everywhere else with short header with an a/r device on the end. It is making me ask the question what is the best shape of an a/r device. Getting on the flow bench and trying different shapes is on the to do list
.
I think you are assuming reverse airflow through the device can be extrapolated to pressure pulses. I'm not convinced that is the case. Does the device clip the wave in proportion to area or airflow reduction. Are they one and the same?

20190414_091045.jpg
20190414_091003.jpg
Put it on a flow bench and see.

I'll speculate on the outcome.

1. It will flow less in both directions than a plain pipe of the same size.
2. The flow in each direction will differ slightly, might even be the opposite of what you expect as diverging flow can cause more drag than converging flow.
No need to speculate on the reverse flow outcome. I have done it.
In standard flow direction, there is a single vena contracta on the device I posted above. In reverse flow, there are two. The measured output approximately correlated with calculated output. Enough so to suggest to me that was the primary effect present.
That does not mean that is what is happening with pressure pulses.
In my head (the only 3D modeling I have). The back pulse does not exist long enough to establish a vena contracta. I think it more likely that the device clips the wave energy based on area reduction percentage and reflects the portion clipped.

I didn't respond to your post. "Does anyone know of any examples of highly developed performance engines that have these devices?" because at about 12 Bar BMEP my application is not "highly developed".
I have used them to good effect, but can't help but think I applied a patch to the self inflicted wound of exhaust porting work that failed to consider the effect of flow reciprocity.
For me the journey to stable lower RPM performance followed in this general order.
1. Reduced camshaft overlap (new cam)
2. Reduced head pipe diameter.
3. Increase total ignition timing.
4, Install AR devices (2)

Application is a half litter NA single.
- Paul
F-BIRD'88
Guru
Guru
Posts: 9802
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Any downsides to anti reversion mufflers/devices?

Post by F-BIRD'88 »

What does CFD analysis suggest if the entry pipe is a slight (choke) cone shape and or is pushed into the chamber different amounts? Forward to reverse flow bias changes?
F-BIRD'88
Guru
Guru
Posts: 9802
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Any downsides to anti reversion mufflers/devices?

Post by F-BIRD'88 »

Are the various colours in the CFD pics local pressures or local velocity(s). whoops I found that..
Last edited by F-BIRD'88 on Sat Dec 18, 2021 3:05 pm, edited 1 time in total.
F-BIRD'88
Guru
Guru
Posts: 9802
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Any downsides to anti reversion mufflers/devices?

Post by F-BIRD'88 »

Just realise a negative effect result can be just as educational as a gain. Don't be afraid to try stuff out.
Don't be afraid to fail a few times.
What goes on in an exhaust pipe is complex.
Bill Chase
HotPass
HotPass
Posts: 446
Joined: Tue Aug 27, 2019 1:11 pm
Location: Michigan

Re: Any downsides to anti reversion mufflers/devices?

Post by Bill Chase »

F-BIRD'88 wrote: Sat Dec 18, 2021 2:47 pm What does CFD analysis suggest if the entry pipe is a slight (choke) cone shape and or is pushed into the chamber different amounts? Forward to reverse flow bias changes?
My thoughts exactly, the Hendren design is in fact a choke. Not just a pipe dumping into a slightly larger chamber.
Post Reply