Anti-Reversion Headers

General engine tech -- Drag Racing to Circle Track

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Re: Anti-Reversion Headers

Post by Bos's5.0 » Sun Jun 14, 2015 9:41 am

joe 90 wrote:The biggest problem here is that everyone keeps going on about flowbenches.

As I keep mentioning.......a flowbench works at 1PSI constant flow.
An engine does NOT.

So why would you want to keep on thinking about it as the best and only tool for the job.
Wrong theory used.......wrong tools used for the job.
Need a bigger hammer?

Hate to break it to ya, but nobody has mentioned flow benches and testing the a/r design. Maybe you need to be in the Cleveland 4V thread... lotsa talk about flow numbers in there. Pretty much all I've seen in this thread is people who have used this design talking about their real world driving and dyno results. OR is that kind of testing the wrong theory and wrong tool?

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Re: Anti-Reversion Headers

Post by Bos's5.0 » Sun Jun 14, 2015 10:39 am

I was just messing around searching and found these things all over ebay.

http://www.ebay.com/bhp/exhaust-cone
port cone.JPG
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Re: Anti-Reversion Headers

Post by Bob Hollinshead » Sun Jun 14, 2015 1:20 pm

Is the distance from head location for the anti-reversion device a positive one based on cylinder volume? Example: are all 454 CI engines going to have the same location? Or does valve timing have an effect?
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Re: Anti-Reversion Headers

Post by Leftcoaster » Sun Jun 14, 2015 1:38 pm

Bos's5.0 wrote:I was just messing around searching and found these things all over ebay.

http://www.ebay.com/bhp/exhaust-cone
port cone.JPG
Imagine a similar cone, the reduced section maybe 3/8" shorter, welded into each primary at the header flange - - from what I recall that's what the original Cyclone anti reversion headers looked like

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Re: Anti-Reversion Headers

Post by modok » Mon Jun 15, 2015 2:29 am

I don't think it has anything to do with physically resisting reversion.

IF you did have a reed valve allowing flow in only one direction, then.....you could try putting it at different points in an exhaust system and find out what happens. On a well designed system it would do nothing positive. There would be a significant loss of power if you put it in the collector and the header is prevented from resonating.
At the head, it would do nothing but add restriction, assuming it didn't melt right away. There does not NEED to be any reverse flow to have positive pressure at overlap, just positive swing of pressure, and in some cases at lower rpms reverse flow happens midway through the stroke and actually improves scavenging. Blowing the intake runner backward at the start of the stroke, at a ways BELOW peak torque rpms, can make a HUGE improvement to torque.
Reverse flow a bad thing? Nope. Have to discard that assumption right off the bat to get anywhere.
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Re: Anti-Reversion Headers

Post by modok » Mon Jun 15, 2015 4:25 am

And finally, what I feel SHOULD BE discussed.
Flow of stuff through an orifice(hole?), as basic concept; depends on....... inlet pressure, size of the hole, and pressure drop.
When pressure drop exceeds 50% flow does not increase further, it is CHOKED. Is choked sonic?? is sonic the hedgehog? Doesn't really matter. I'll call it choked past 50%.
The velocity of the stuff coming out of the hole depends on the inlet pressure and pressure drop, or past 50% drop, just the inlet pressure. Mainly the inlet pressure.
Yes the properties of the stuff come into play but that's more or less a constant.

The velocity of the stuff coming out of the hole depends on the inlet pressure, and drop%. (I said it twice, very important)

Why is this important? well, because during blowdown, if the valve is opened fast enough, the velocity coming out of the port is tremendous. Like a rocket!
Yall understand venturi.....right? venturi with flow, you measure at the small point........low pressure(uncle Bernoulli), then it expands at say 7 degree, and slows the flow down, now you have higher pressure. It recovers the pressure and pulls a bigger differential across the small part. Tis a venturi.......or the divergent part anyhow. 7 degree is a pretty good taper to use for a carburetor. If it diverges too fast the air won't follow, and it won't work, as you know.
Of course how it's working is the flow is HITTING the slower stuff in front of it and this is what slows the flow jet down, and it has to happen gradually enough to stay orderly. If the tail of the venturi was in SPACE, in vacuum, then the flow might just travel in a straight line, and not expand, and not follow the taper (I think???).........but if other end of venturi is in space.... then there would probably be more than 50% pressure drop across it also.

And.........what I am struggling to somehow explain, is taking the ROCKET THRUST coming out of the exhaust port and turning it into PRESSURE in the header tube, gets strange at high speeds. For reasons I'll claim are assumed (pipemax says so), the port is smaller than the header tube. So the JET, has to expand and slow down to produce pressure in the header tube. As a human, air breathing creature, I expect 7 degree taper would work great.
Actually no. Tests show it won't slow down that fast. In my simulation software, I can connect a little pipe to a big pipe and through the magic of make-believe the flow suddenly matches the size of the big pipe right away, but not in the real world. In the horrible book they found it does not slow down for, in some cases, a foot down the pipe. This still happens.
And that is why the first pressure traces in this thread below differ from predicted.
(open in new window please) viewtopic.php?f=15&t=37398&start=30
The pressure measures LOW halfway through blowdown because the JET of velocity in the pipe has not expanded and slowed to the header tube size!! Or the very high earlier velocity has accelerated the gas down the tube to high velocity, and so there is virtually nothing in the pipe TO slow the flow as it dischrges slower. Actually both. High velocity reads low pressure(the bernoodle affect). Down the pipe 6 or 12 inches it is finally slowing down and reading higher but there was no sensor hooked up there I guess. So what IS in the pipe during that dip of pressure? I guess there is just a jet following the walls and empty space around. Maybe. Once the cylinder pressure goes down then the thrust and velocity is lower and you see pressure come back up, as not reverse flow but certainly flow slows, and pressure creeps backward.
If a header tube gathers no pressure then It's not doing it's job very well, or you might say the pressure coming back UP again is......what they call "monkey motion." Some of that volume is not functioning positively here in the first half. Then again what's the harm? There could be other reasons you want the header size big all the way to the port(doppler), then again, it does not NEED to be big, so........why not keep it small 6 inches out, 8 inches out. Or approximate a very slow taper. Calvin Elston has found some good results staying small till a ways out I read. If you take the VOLUME that was taken out by staying small, and put that volume 6-12 inches down the pipe where the jet finally does slow down, then.........well, maybe you HAVE something. You have stored pressure, with reduced monkey motion, and higher velocity near the port. It is a small thing, but when deciding if the AR chamber is part of a well balanced breakfast we have to look deep.

The claimed inventor of the thing, did understand this reality and said it with much less words. I'm impressed.
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Re: Anti-Reversion Headers

Post by joe 90 » Mon Jun 15, 2015 5:35 am

modok wrote:And finally, what I feel SHOULD BE discussed.
Flow of stuff through an orifice(hole?), as basic concept; depends on....... inlet pressure, size of the hole, and pressure drop.
When pressure drop exceeds 50% flow does not increase further, it is CHOKED. Is choked sonic?? is sonic the hedgehog? Doesn't really matter. I'll call it choked past 50%.
.

https://en.wikipedia.org/wiki/Choked_flow

So what need to know is that during choked flow any decrease in outlet pressure doesn't increase the flow but an increase in inlet pressure DOES increase the flow.
................................................................................................................................................
Choked flow is a limiting condition where the mass flow rate will not increase with a further decrease in the downstream pressure environment while upstream pressure is fixed.
...................................................................................................................................................
You can't compare it to a rocket because a rocket is constant flow and an engine IS NOT.
It flows in waves which travel at the speed of sound.

Then once you understand a bit about waves there's another factor in play which is "resonance"

https://en.wikipedia.org/wiki/Acoustic_resonance

That means that the dimensions of the pipe factor into the calculations.


All exhausts are noisy.
Noise is lost energy.
A proper anti reversion header will reduce the noise level because the waves are being converted into a more constant flow.
At the same time the energy is being used to extract the exhaust gasses.......that if it's done right.
Last edited by joe 90 on Mon Jun 15, 2015 6:18 am, edited 1 time in total.

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Re: Anti-Reversion Headers

Post by modok » Mon Jun 15, 2015 6:18 am

ok, yeah. I'm not real sharp on rockets honestly. Just borrowing the idea of a stream, or jet, and if the stream hits nothing, it develops no pressure.....it just GOES.

The blowdown pressure "kink" is so clear in my mind now I wonder why Vannik's SIM doesn't show it? Since, as cylinder pressure falls the.... rate of discharge will slow, and just from simple momentum, it should be there. Of course that.......is because I don't know how the sim works. Really, I don't know much.
Resonance I know well. All of this is about the first phase of building pressure, I have not covered what happens after that.
But short story, that's what a header primary DOES, is it builds pressure, then gains velocity, and then pulls vaccum later on. How this changes the shape of the curve is another consideration. More taper you get more of a triangle wave form, more volume toward the closed end gives more towards a square wave. Just the primary.........and we haven't envolved multiple cylinders and interferance quite yet!!
And I've said doppler, to mean the slowing of a return wave due to this wave traveling against velocity.........and I know it's not entirely correct but, if you've got a better name, I'll consider it.
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Re: Anti-Reversion Headers

Post by lada ok » Tue Jun 16, 2015 4:09 pm

About 1/2 way down the page ..."AR" pipes

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Re: Anti-Reversion Headers

Post by vannik » Sat Jun 20, 2015 7:34 am

modok wrote:The blowdown pressure "kink" is so clear in my mind now I wonder why Vannik's SIM doesn't show it? Since, as cylinder pressure falls the.... rate of discharge will slow, and just from simple momentum, it should be there. Of course that.......is because I don't know how the sim works.
Maybe there isn't a kink. See attached.
Choked.pdf
This shows that even though the velocity does not increase, the mass flow does, as long as the upstream pressure increases. Hope this helps.

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Re: Anti-Reversion Headers

Post by modok » Sat Jun 20, 2015 3:41 pm

Thank you. Reading that I see some of my generalities about choked flow are not entirely accurate when scrutinized, but they are still ok generalities LOL
The kink has always been present. See page 86 figure 5:7
Author believes these kinks are from residual waves, however, I do not agree. Such kinks tend to be present in many cases a long primary is used.
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Re: Anti-Reversion Headers

Post by digger » Tue Oct 10, 2017 4:06 am

so how do you test the effectiveness of an anti reversion device without a dyno? my suspicions are you have to a pulse flow to see the real effect and steady state is not going to show the effectiveness anywhere near what happens as there is a time dependency for the reverse flow to "fill the void" ?

here is an AR collector that mentioned elsewhere on here that might work #-o

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Re: Anti-Reversion Headers

Post by David Vizard » Tue Oct 10, 2017 3:58 pm

Only just found this thead.

Since my name came up a number of times in the early postings and some not so accurate statements where made I thought I should say something to set the record straight.

I was asked to do the A/R header story by magazine editors wanting such. As I recall none of the published tests were done on my dyno. Most of the tests were done on JUNIOR jOHNSON's dyno in NC. I was along mearly to witness the results of these tests.

Jim Fueling,who claimed invention, did, as I understand it, have a patent even though there was previous work along these lines which should have qualified his work as 'prior art'. Indeed I had been working on 'uni-directional system flow' for at least two years before I had even heard of Jim Fueling.

My work did not focus solely on the exhaust but took into account everything from the intake stack to the tip of the exhaust pipe.

There were many claims that Fueling made that proved to be a little off course. For one, subsequent dyno testing did not substantiate the need for a 180 degree header. Also because Fueling did not fully grasp what was happening here he stuck to the use of a cone to create the 'anti-reversion' effect. Had he spent more time on the flow bench he, as I did, would have found that a cone was far from the best means of generating an anti-reversion effect on a typical Detroit V8 engine such as a SBC or SBF.

A point to note here is that to be really effective any anti-reversion mechanism needs to be as close to the source of what it is supposed to be working on. For instance any anti-reversion devise that is half way down the exhaust pipe will not be remotely as effective as one adjacent to the exhaust valve.

I did a lot of work on A/R intake valves but the project that took the biggest chunk of my time here was an emmission legal Corvette header for about 1986-on SBC powered Corvettes. The end result was about a 25 hp and 20 lbs-ft increase in output plus a significantly cleaner cold start cycle as well as a reduction in raw emmissions. Sound levels were also down.

I am sure this would have sold well but management problems with the company the work was for caused the project to be dropped before quantity production could be put in hand.

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Re: Anti-Reversion Headers

Post by joe 90 » Tue Oct 10, 2017 4:54 pm

Nicola Tesla patented the idea in 1920.

https://en.wikipedia.org/wiki/Tesla_valve

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Re: Anti-Reversion Headers

Post by David Vizard » Tue Oct 10, 2017 5:08 pm

joe 90 wrote:
Tue Oct 10, 2017 4:54 pm
Nicola Tesla patented the idea in 1920.

https://en.wikipedia.org/wiki/Tesla_valve
Why does this not surprise me. Tesla - what a brain!!!!

Thanks for posting this Joe. I am something of a Tesla fan but had not seen this.
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