ITRacer121

I am told that my Vision header has anit reversion chambers? I was wondering what they are and how they work?
TIA

00Red_SiR

I don't know what your header looks like so I can only give you a general answer about what it is and how it works.

It's usually a larger sized chamber close to the exhaust port in the primary tube of the header and functions like a step. It's designed to keep the exhaust gasses from flowing backwards into the cylinder before the exhaust valve closes. This will help ensure that the cylinder gets filled with the freshest intake charge that isn't contaminated with leftover exhaust gasses, which will make more power. Like fluid, it's harder for the exhaust gases to travel backwards and upwards over a step than it would be if it was a simple round tube with no steps.

That's what it is and how it works in a nutshell, I'm sure the header manufacturers like Dave from SMSP etc could give you more detailed explanation.

ITRacer121

that makes perfect since
Thanks

Padawan

Your header doesn't have anti-reversion chambers. Certain design features can limit reversion, but they aren't actual anti-reversion chambers.

Kengs

United States Patent 6336471

Inventors: Feuling; James J. (686 Ash Ave., Chula Vista, CA 92010)

Abstract:

An improved fluid flow system for enhancing fluid flow through an opening. The first embodiment uses a first extension member for extending an opening through a perpendicular surface and a second extension member with a generally converging introductory section secured in a sealed overlapping relationship to the distal end of the first extension member. A second embodiment uses a pair of conduits of equal cross-section with a bulbous section therebetween with one of the conduits inserted into the bulbous section. A third embodiment with unequal cross-sections with the smaller diameter conduit inserted into the larger diameter conduit and sealed thereto for forming a continuous conduit.


That's the patent that Hytech is using under license.



From Hytech's site:
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">REVERSION is the secondary pressure wave that travels back up the primary pipes and enters into the cylinder on valve overlap. As this pressure wave travels back up the pipe, it brings with it all the residual gases still left in the pipe. This is what contaminates the fresh intake charge. Enter in stepped headers and ANTI-REVERSION chambers, placed at strategic locations in the primary pipes. These methods are employed to tune the arrival of the exhaust wave and to diminish the effects of the high pressure in the pipes. The results are higher volumetric efficiency and more power.</TD></TR></TABLE>

ShaunRR

IMO, they are a band-aid for a less than optimal header design.

Jowee

http://www.jhpusa.com/catalog/...9efda



I called them to see if it was a typo, but the guy assured me it wasn't.

Padawan

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ITR 98 1162 &raquo;</TD></TR><TR><TD CLASS="quote">I called them to see if it was a typo, but the guy assured me it wasn't. </TD></TR></TABLE>

You should call back and assure him that the Vision header <u>doesn't</u> incorporate anti-reversion chambers.

Quitripin

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Padawan &raquo;</TD></TR><TR><TD CLASS="quote">

You should call back and assure him that the Vision header <u>doesn't</u> incorporate anti-reversion chambers. </TD></TR></TABLE>
I believe it's a patent design

A20A1

,,,,,,


Modified by A20A1 at 4:14 AM 7/9/2006

A20A1

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Padawan &raquo;</TD></TR><TR><TD CLASS="quote">You should call back and assure him that the Vision header <u>doesn't</u> incorporate anti-reversion chambers. </TD></TR></TABLE>

I don't see any chambers on the Vision Header either

Maybe they are refering to something else or the pic is wrong... or perhaps they use slightly larger exhaust ports on the flange then the ports on the head to act as a step???

00Red_SiR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by A20A1 &raquo;</TD></TR><TR><TD CLASS="quote">
...it sounds like someone is suggesting they block negative expansion waves... the negative wave is what gives you the scavenging effect. Scavenging = so blocking the scavenging wave isn't a good thing... timing when it reachs the overlap period is.

</TD></TR></TABLE>

Negative (returning) expansion waves are undesirable in headers and manufacturers often design in things like steps and anti reversion chambers to help reduce this pulse. Scavenging is very desirable but it is a "suction" created behind the departing pressure wave pulse, when the exhaust valve opens. That suction helps create a vacum in the cylinder so it will fill more completely with a fresh intake charge and therefore make more power. A Negative returning pressure wave HURTS the scavenging effect because it actually pushes exhaust gasses back into the cylinder reducing cylinder filling efficiency.

Normally, every time the exhaust pulse reaches a point in the exhaust where it opens up into a larger area like the collector, a reverse pulse wave is reflected back up the pipe towards the exhaust valve. Negative pulse waves are going to happen in every header design so the best header designs incorporate features that help to reduce this effect as much as possible.

Certain design features like making the primary tube opening slightly larger than the exhaust port and smoothing the transition or "step" into larger diameter piping help reduce the negative pressure pulse wave. The first anti reversion feature I mentioned creates a physical step for the returning pulse wave to overcome, in order to re-enter the cylinder. The smoothing of the transition area when moving into larger piping which can be in the primary tubing and collectors helps to maintain velocity and significantly reduce the strength of the negative pulse wave.

There are other things that can be done like using cone shaped collector extensions and designing steps into a headers primary tubes at specific distances to help cancel out negative pressure waves. Building headers isn't an exact science, but it is a science and simply building them using different lengths and diameters of tubing that work isn't always the most effective way to make power on every application.

A20A1

vvvv


Modified by A20A1 at 4:15 AM 7/9/2006

00Red_SiR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by A20A1 &raquo;</TD></TR><TR><TD CLASS="quote">

I dunno... both my engine building book and the site quoted above say that the negative waves assist gas outflow.
Maybe I am mis-labeling or mis-interpreted what hytech labels as a negative wave in relation to what I'm describing and thats where the confusion exists...
</TD></TR></TABLE>

Either you are, or I am slightly off on something here....maybe one of the header guru's could step in here and help clarify this?

S2 INSIDER

i asked the people at skunk about AR chambers and they started laughing!

they dynoed headers with and without and the difference was only +/- 0.2 hp (within standard deviation) and the rate at which the engine acclerated was the same.

i believe "snake oil" was the quote.

slofu

it seems as though any difference is not so apparent on the dyno, but iirc, John said that on the track he did back-to-back runs with 2 identical headers, except that one had the chambers, and one didn't. the one w/out beat the other on the dyno every time, but the one with them won every time on the track. considering the fact that they look harder and more time consuming to include, and increase cost (patent royalties and cost passed onto customers), i don't think that John would go through the trouble (and perhaps lose more business due to cost) if they did so little.

my guess is that they make the biggest difference between points of lower/higher acceleration, e.g. on a road course where the throttle and load changes more often. since, as rpm decreases, each exhaust pulse also loses speed, when you let off of the throttle, say, going into a turn, perhaps the intake stroke actually pulls some the spent exhaust at lower speed (throttle closed, so less air/fuel) back into the chamber (reversion), which spoils some of the fresh intake charge, costing power and recovery time as you open the throttle and pull out of the turn. in drag racing, this would occur at each shift point. since the "stacking" of each exhaust pulse onto the last, slower pulse adds heat/expansion to it, when the pulse starts to revert, it's still expanding, so much of it finds its way into the outside of the AR chamber, it loses heat/velocity such that it can't make it back into the combustion chamber before the next, faster pulse pushes it back in the right direction.

granted, this is also why stepping the tubes helps, but maybe the chambers give the slight edge that some require- just as might angling the primaries at the flange to follow the port exit angle of each port and using 'D' shapes to maintain velocity and reduce separation/ turbulence in tighter bends.

if you could measure recovery time at different throttle positions and loads from, say, dropping from 8000 rpm to 7000 rpm and pulling back up to 8000 rpm again, i think that the AR chambers might still prove beneficial, especially when engine deceleration is sudden or when loads are higher (in gears 3-5 with one of the usual final drive ratios and a fairly common wheel/tire size), going from high to low throttle positions and back, quickly.

when the throttle is slammed shut at higher rpm, there is little air taken in or exhausted, but the valves are still moving normally, and the piston speed is still very high, so especially when the cams include a decent amount of overlap the gas in the area of higher pressure (the header) will flow (back) to the lower-pressure area (the cylinder) created when when the piston descends on the intake stroke (when the exhaust valves are still slightly open). higher rpm will mean more pulses, higher piston speed means harder pulses, and greater stroke means longer pulses, all working together to pull the exhaust back into the cylinder. the additional area of the AR chamber's outer edge simply provides an intermediate pressure drop to create turbulence, separation, and cooling of any gas flowing backwards, utterly ruining the flow before it reaches the combustion chamber and corrupts the fresh intake charge.

SMSP

How much faster and on what length course?

Back to back tests on a road course are a hard way to prove something like this. There are way too many parameters that change.

Tire pressure, tire temp, brake points, brake temps, air temp, track temp, sunny vs cloudy, consistency in every turn. Anyone who road races has gone faster and slower from lap to lap without making any changes.

Nascar doesn't use them and they are on/off throttle at least twice per lap. I haven't seen them on F1 either. Fact is they were originally developed for WWI airplanes that run at very low rpms with many cylinders.

Ekasey

The whole basic idea of header tuning and theory is to time the negative wave so it arrives at the cylinder during the period of overlap to promote scavening.

Fact of that matter is that this negative pressure wave is travelling at the speed of sound , the gas particles and the combustion by products portion are only going to move slower as they travel down the tube and expand and it is unlikely that if they do travel back up the tube they are not going to arrive between the period of overlap.


Modified by eLusive ek4 at 8:25 PM 3/4/2005

DOHCsideracing

There are a lot of people that know better than I on a lot of this header theory/practice, but what I have read (and my understanding of it...) is that the "pressure wave" that we are referring to, travels at the speed of sound (like Casey said), and doesn't actually "flow" with the exhaust stream. The pressure pulse rides "through" the exh gases, but isn't really effected by it (other than by its desity to determine its speed).

In my mind (which has been known to be wrong from time-to-time) it seems AR chambers, or steps, etc. used to get the pulse not to revert will hurt low rpm tuning more than the high rpm stuff b/c the pulse at low speed have to make numerous trips down and back up the header (speed of sound), then it has to pass over these steps each time, and each time the pulse is weakened.

Again, from what I have read, the 1st order pulse (one round trip) is the strongest, but is very, very narrow, and is usually skipped, but the 2nd order, and third order frequencies are almost as strong and have a better window so those are very desirable to tune for. The higher and higher order you go, the less effect you get, until about the 5th one which is pretty much nothing. The 5th one is at a very low rpm. If 1st is around 8500 rpm, the 5th would be around 4,000.

I always thought the "stepped" primary designs were to keep the velocity of the stream approximatly the same since the gases are still expanding as they travel down the pipe, so you needed a bigger flowing area to get the less dense exh out.

H-T gurus, please shed some light on my misguided thoughts...
Adrian


Modified by DOHCsideracing at 10:41 PM 3/2/2005

S2 INSIDER

theoretical mumbo jumbo!

i heard that even Fueling engineering said AR chambers didn't work on high-rpm, high exhaust speed modern day engines.

slofu

the best way to test them is prolly to try 2 identical headers, save for one having the AR chambers, on the same engine on an engine dyno, and to measure recovery times, since that is what they're supposed to increase.

da'ee

I talked to John about the anti inversion chambers and the D shaped ports. He uses them on the headers he makes for race teams. He said the anti inversion chambers dont make more power, but help with the throttle response. The D shaped ports make a little more power becuase they speed up the air flow. He also said that race teams are looking for anything they can get.

da'ee

CART Toyota Atlantic. They use the 1.6 liter Toyota 4A-GE engine. The series states that the engine has to remain stock and can only be balanced, the only way they can up the HP is with the header/exhaust. So the race teams are looking for anything they can get out of their headers. Whether the anti-inversion chambers and d shaped ports really work and have an effect, Im not sure. But I think for a street/track car the anti-inversion chambers and the D shaped ports arent necessary.

And the price for Hytechs header with the anti-inversion chambers and the D shaped ports is $1700! His regular header is $1300 which includes the anti inversion chambers. I really dont think its worth it. Considering you wont see any gains and Toda/SMSP headers perfrom just as well and are around $900-1200.

ShaunRR

The Toyota Atlantic motors are not stock 4AG motors. They are, however, sealed spec motors. Those motors make around 240bhp and spin to over 10k rpm.

DonF

Just because the Toy Atlantic engines are over $30.000 each you do not think they are stock? Last time I looked (2 years ago) some teams used 4-2-1 headers on street courses ans 4-1 on the reg courses and no anti-reversion chambers, and yes, John made alot of the headers.