Anti-Reversion Headers

General engine tech -- Drag Racing to Circle Track

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modok
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Re: Anti-Reversion Headers

Post by modok » Thu Jun 11, 2015 3:05 am

I put some under my carburetors five years ago, in such a way they would not change velocity, and would function as reverse flow restrictions just as Fendermate describes.
It didn't seem to make any difference at all. I wasn't expecting anything in particular, just making phenolic insulators and while I was at it made a bunch of gonzo ones with tubes and vanes and screens on them to see if anything would happen.

I think the concept HAS BEEN tested thoroughly, and for those the keep at it, probably learn it doesn't lead anywhere, but IS another tool in the toolbox.
For some, a tool that rarely gets used, or never, so you throw it in the bottom drawer as ballast..........
And but nobody wants to give their hard earned secrets away entirely when they have bills to pay.

I don't have any dreams to make money with this stuff, and I figure even if I say something brilliant nobody will notice because they think I'm a nutjob, and I probably am.

It is a GREAT story, many great minds thinking alike, across decades, testing out this concept, to this very day.

WHO coined the term anti-reversion?
Glen Urban

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Re: Anti-Reversion Headers

Post by joe 90 » Thu Jun 11, 2015 4:03 am

It's really not a lot different from using a diode in an electrical circuit.
Gas flows in waves which move in both directions at the speed of sound.
A diode allows more movement in one direction than it does in the other.

In fact it's more like a diode, inductor and a capacitor (LC filter), the size of the chamber along with the length of the pipe determines the frequency, or the RPMs at which it's effect is at it's max.

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Re: Anti-Reversion Headers

Post by MadBill » Thu Jun 11, 2015 9:39 am

One of my quests in life is to develop a 'dollar diode'. I'm getting close, but so far all the protoypes have operated in reverse.. #-o
Felix, qui potuit rerum cognscere causas.

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Re: Anti-Reversion Headers

Post by Bos's5.0 » Thu Jun 11, 2015 10:37 am

MadBill wrote:One of my quests in life is to develop a 'dollar diode'. I'm getting close, but so far all the protoypes have operated in reverse.. #-o
Genius =D>

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Re: Anti-Reversion Headers

Post by bmcdaniel » Thu Jun 11, 2015 11:18 am

MadBill wrote:One of my quests in life is to develop a 'dollar diode'. I'm getting close, but so far all the protoypes have operated in reverse.. #-o
Yeah, but they're Canadian dollars, not that big of a deal...

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Re: Anti-Reversion Headers

Post by MadBill » Thu Jun 11, 2015 11:27 am

I figured I'd do the development work with baby bucks to keep the costs down.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Anti-Reversion Headers

Post by groberts101 » Thu Jun 11, 2015 12:18 pm

While the potential gains are proven.. I don't believe it's possible to do it all in the exhaust alone and the entire engine should be developed with AR in mind. Implementing AR from inlet to tailpipe could/would/should give the largest degree of gain and allow the greatest power spread. Bigger problems arise when trying to avoid potential energy losses while implementing that many "diodes" into a system.

Also don't believe that AR designs are advantageous for all motors since they're primarily focused on reducing intake reversion at lower speeds where velocity and momentum haven't shown up yet. Although I do realize the added acoustic advantages seen beyond that. In drag race only applications using big cams to supply overly large intake and exhaust tracts.. aside from maybe hitting the converter a bit faster/harder coming off the brake.. will typically only gain power below peak torque but probably shouldn't give a flying squat once they really start singing where they were designed to operate at peak efficiency anyways. As Calvin and a few other bright individuals have mentioned many times.. get the velocity and improve blow-down length while still avoiding choke/stall prior to the necessary power/flow requirement?.. and you've already won most of the battle in that you've successfully made a natural dam to keep reversion tamed down.

AR for road racers and street/strip?.. now that's another story altogether.

I've always been fascinated by this subject matter and will build my SBF to be a full on AR style motor. Much work to be done to avoid killing much top end power while heavily shoring up the lower ranges. Cam guy might be in unknown territory too as I ask for another bit of duration and lift than would typically be rec'd for my usage model. Probably a good reason why we don't see it(full AR engines) done from inlet to tailpipe so I plan on leaving myself many "outs" by implementing modular and removable designs in various locations throughout. Biggest problem is trying to interpret flow numbers and much reverse flow work will have to be added into the mix to better quantify any potential gains to be had.

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Re: Anti-Reversion Headers

Post by hoffman900 » Thu Jun 11, 2015 6:47 pm

A/R Chamber: A good friend of mine implemented one in the tailpipe in a road race car per Calvin's recommendations and is very happy with how it's cleaned up the engine's response off the cam.

I think they are a great tool for cars that operate 'off the cam' from time to time.
s Calvin and a few other bright individuals have mentioned many times.. get the velocity and improve blow-down length while still avoiding choke/stall prior to the necessary power/flow requirement?.. and you've already won most of the battle in that you've successfully made a natural dam to keep reversion tamed down.
This. I think everything else is just icing on the cake. Do I think these have applications in drag racing? No, but I think circle track and road racing they do.

https://www.youtube.com/watch?v=99w2fOvmMb0

This car has all of Calvin's bells and whistles between the exhaust port flange to atmosphere... I think it's safe to say it's pretty responsive at all throttle positions / rpm levels.
-Bob

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Re: Anti-Reversion Headers

Post by wyrmrider » Thu Jun 11, 2015 7:47 pm

Did you stick some in a tunnel ram?

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Re: Anti-Reversion Headers

Post by hoffman900 » Thu Jun 11, 2015 8:03 pm

wyrmrider wrote:Did you stick some in a tunnel ram?
I think tunnel rams take care of it by the plenum size and shape. Same goes for a single plane intake + add in carb spacers / shear plates.

Calvin Elston illustrated this to me one time in talking about an exhaust system he designed for an outfit... A certain design performed fantastically on an engine with a single Holley and all the tricks. What was essentially the same engine with individual Webers, couldn't take throttle and was spitting gas out the carburetor.

Where I can see a A/R type system work is on an individual runner carburetor set-up. However, anyone who has picked up an aerodynamics book, will tell you drag occurs on the backside (where the step would occur). I'm hesitant to try without first seeing how something like that would work on a flowbench. IMO, due to the gas speed and pressures involved, I don't think the exhaust is as sensitive to this drag as it would be on the intake.
-Bob

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Re: Anti-Reversion Headers

Post by Fendermate » Fri Jun 12, 2015 1:22 am

To start with, thanks Leftcoaster for the info on Jim Fueling. It makes me real happy to see that someone took what I started (other than the ones that stole it), understood the potential and continued to build it into something great. I wish he was still with us and I hope his company continues to flourish.
Yes, there is reversion on the intake side but for a totally different reason. During my time experimenting, my main concern was the exhaust contamination of the combustion chamber caused by reversion. Not only did it contaminate the fresh air/ fuel mixture, it also took up valuable space and because of overlap, it would also enter the intake runner. That was all taken care of by AR on the exhaust side. Torque curves were now flatter and higher with positive gains even at higher rpm's.
I then paid attention to the intake side. Even though most of the issues were taken care of, there was still the issue of the potential of reaching 100% volumetric efficiency over the full rpm range. Of course there are bends, turns and restrictions flowing around valves. So, maybe 100% isn't attainable. To get a better picture of what was happening I set up 4 vacuum gauges in one runner of a dual plane and notice way too much activity closest to the head, even showing pressure spikes in comparison the rest of the runner. These 'pressure' spikes were happening at the moment the valve closed.
This made sense. With the valve open, air velocity would be at its peak and slamming the door shut caused the pressure build up. What's interesting is that this was affecting the complete runner to a gradient degree and the next time the valve opened, this reversing pulse of pressure had to be overcome to attain full intake velocity again. I retested with a single plane and it was still there but definitely not as pronounced as a long runner and I knew a tunnel ram would prove even less.
To counteract this affect, I purposefully mismatched the head ports, tapering the bores larger than the intake runner, similar to an AR valve. This would have no affect as a restriction to flow, only an additional space in the port to absorb the pressure build up.
It worked. The pressure spikes subsided by approximately 90% and intake vacuum increased from 18 in. to 24 in.
This is the engine I took to the dyno with unheard of results. That was in 1980.
By this time, I ran out of money to continue.
There was one thing we noticed during testing; no heat.
You would think that creating more power would result in more heat, requiring a more efficient cooling system but it took way too long for the engine to reach operating temperature.
It took a while but I figured it out.
Because of reversion, we're not just dealing with spent exhaust, but also the heat it contains. Creating an effective AR system also keeps the 'latent' heat out, giving us a cooler, denser charge.
For a race engine, this is good. But for a normal street engine, a stationary motor, a marine engine and even a lawn mower, this is huge.
30% increase in power, 30% increase in fuel economy, lower operating temperature and a significant drop in NOX, HC and CO.
There's still so much to do and, as you can tell, I am so excited to talk to people who know what I'm talking about.
Thank you so much for listening.
Bob Paff

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Re: Anti-Reversion Headers

Post by Leftcoaster » Fri Jun 12, 2015 2:03 am

Those who have developed anti reversion devices and techniques seldom discuss them for commercial reasons

Larry Widmer is an exception, perhaps because he's one of the foremost originators - - his http://www.theoldone.com site provides a wealth of information, and although most is specific to 4v 4cyl Honda engines other 4v per cyl makes and models are included

Radical changes to the combustion chamber, piston crown shape, valve head and underhead shape, valve seat and throat, port contour, a smaller port outlet i.d. than header primary i.d., Feuling style anti reversion chambers not more than 12" from the header flange, then a conventional 4 into 1 collector - - all work together to minimise exhaust reversion so otherwise radical cams may be used while still passing emissions tests

Lower exhaust manifold temps when consuming the same quantity of fuel is symptomatic of a more efficient combustion chamber burn producing more power due to higher pressures acting on the piston crown

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Re: Anti-Reversion Headers

Post by Bos's5.0 » Fri Jun 12, 2015 9:45 am

Fendermate wrote: To counteract this affect, I purposefully mismatched the head ports, tapering the bores larger than the intake runner, similar to an AR valve. This would have no affect as a restriction to flow, only an additional space in the port to absorb the pressure build up.

Bob Paff
Could you explain this a little? Did you make the intake manifold ports Larger than the head ports to create more volume? Did you blend the transition or leave a step? LIke putting a 4V Cleveland intake on a 2V head?

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Re: Anti-Reversion Headers

Post by groberts101 » Fri Jun 12, 2015 10:08 am

Bos's5.0 wrote:
Fendermate wrote: To counteract this affect, I purposefully mismatched the head ports, tapering the bores larger than the intake runner, similar to an AR valve. This would have no affect as a restriction to flow, only an additional space in the port to absorb the pressure build up.

Bob Paff
Could you explain this a little? Did you make the intake manifold ports Larger than the head ports to create more volume? Did you blend the transition or leave a step? LIke putting a 4V Cleveland intake on a 2V head?
read it again Boss.. I believe what he said above is that the heads entry is notably larger than the intake manifolds exit size.

As for the no restriction in flow?.. well, I don't buy that one little bit because it's well known that's just another band-aid approach for over-cammed and/or too large CSA setups that can exhibit increased low-mid speed reversion issues. Just like too large a step from the exhaust port to the headers primary tube size.. it causes the abrupt edges of the flow column to roll off the edge and start a tumbling mess of things further downstream. For lower speed app's, the "lessor of two evil's" rule kicks in and you get what you get out of the deal. Most people only want to see the net gains without looking too hard at the potential downsides.

IMO, severely mis-matching exhaust ports is bad enough(higher compression and higher speeds just makes it even worse).. but doing that on a marginally sized or improperly designed intake port, plus add a "bad cam choice" into the mix, can and often does lead to a mess of other issues leading up to the short side and pocket area. In the worst case.. you can very easily make a port become "noisy" on the bench and cut your own nuts off in the process. the power band narrows up on you and the high speed pressure recovery will go straight into the crapper too. Make the port right for the intended application, size and shape is everything here, and you won't need as big a band-aid in the end.


And not to be the doubting Thomas here all the time, but I would also like to hear from anyone else who's ever witnessed varying degrees of manifold vacuum fluctuations with "4 gauges sampling along the same port". Me thinks it's not possible to measure such variations with simple vac gauges like that.. or at the very least, the human eye isn't fast enough to see any "spikes". Would love to be wrong though and would happily do some additional "gauge testing" myself to coincide with some reverse flow bench modeling of various AR designs on the intake side of things.

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Re: Anti-Reversion Headers

Post by levisnteeshirt » Fri Jun 12, 2015 3:58 pm

I have to wonder if all these tapered spacers , are actually reversion funnels ,, ,, cutting the collector exit at an angle , to spread out the time of the exit of the pulse might help I would have to think ,, and not give it such an efficient conduit to send the pulse backwards

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