Hey Guys,

I've read lots of talk about expansion chambers people have been testing in their exhaust systems. Has anyone tried playing with anti-reversion chambers in the headers? A buddy of mine was taking about it, so I did a search which didn't come up with any results in this forum.

 

I think they would be a great idea, but the scavaging from legnth tuning and expansion chambers might be enough. I'm not sure if antireversion chambers have really been shown to make more power yet.

 

Something like this???

 

No that's an expansion chamber.
http://www.onecamonly.com/naturally-...na-header.html
http://www.honda-tech.com/showthread.php?t=1161501

 

That looks like a 2 stroke exhaust design applied to a rotary. Too bad 2 stroke exhaust design doesn't work on a rotary and each pipe would have to be independent anyways.

 

Where have you been? Expansion chambers work well my friend. I don't know about that second part in the second pic though.
https://www.rx7club.com/1st-generation-specific-1979-1985-18/racing-beat-exhaust-dyno-compairisons-823229/

 

I didn't say expansion chambers don't work on rotaries. I said 2 stroke exhaust design doesn't.

 

LOL. Does anyone know what the heck is in that second picture?
(on topic)
If you look at the first pic closely it looks af if there might be an antireversion chamber right after where that exhaust collects. I'd really like to see some back to back engine dyno testing of a header with and without these chambers. They seem to be previlent in the Honda world and formula racing cars. Formula Ford, Formula Atlantic, etc...

 

I was under the impression that an anti-reversion chamber works best if it's closer rather than farther away from the exhaust port. The goal being to limit reversion of exhaust gases during overlap. I'm actually kind of surprised that they haven't been popular in rotaries for a while.

 

the pic above has an expansion chamber...
This pic has antireversion chambers

 

Well I guess that answers my question as to if anyone has used them on here. I guess will find out how well they work when someone tries them.

 

I have put them on a stock 12a which they run in a class here in nz,with modified stock 4 barrel carb and exhaust being the only mods allowed we saw a 8whp gain when fitted. 124whp up to 132whp.this was on a dynodynamics dyno.
I cant remember what the torque did as it was a good 5 years ago.
needless to say the car was quiker around the track.
I have yet to try on a heavily ported engine,to busy playing with turbos

 

I wonder if it something that would hurt flow in High HP applications and become a hinderance. I guess the only way to know is to try.

 

Shouldn't hurt top end flow much if at all. Only thing that might hurt the flow is the change in volume slowing down the gases


BC

 

It's so miniscule that it isn't an issue.

 

I guess the real question is about how much reversion is really seen on a rotary. Is this really an issue?

 

exhaust scavenging for the win.

 

It's actually more of an issue on a peripheral port exhaust than on any other type of engine. The more rapidly a port opens and closes, the more intense these pulses. I don't like to think of it as reversion so much as a pressure wave which is really just an easier way of thinking of it. When a positive pressure wave hits a larger area, it sends a reflected wave back up the pipe but this time it is 180 degrees out of phase of the original wave. Depending on the pipe length this could be a constructive wave which reinforces a suceeding wave and build on it or it could be destructive and partially cancel it out. Both will actually happen at times. It's all based on rpm. Even a true dual system will succumb to this phenomenon as the end of the pipe is a large area of infinite size. You can't escape it. Different pipe lengths and rpms will determine how many waves can be in the pipe at once and in what way they interact with others. An antireversion chamber is used to help absorb some of these waves.

 

I wonder why I've never seen one in a rotary application. Mazda didn't even use them in any of their racing applications. Is this a newer technology?

 

A while ago I picked up this exhaust for "parts" but curiosity is getting the better of me... Wondering how it runs and what it sounds like.

BASTARD,
Do you know anything about it? It looks like it was made to go over the top of a 12a.

 

actually it turns out you have seen it, there is an SAE paper about the FC exhaust sleeve manifold design and part of it is to make it quieter, and part of it is an anti reversion device.

 

I remember arguing that like 10 years ago here- glad there is a SAE paper to validate my opinion.

Just looking at the exhaust sleeve with its one big oblique flat side it looked obvious to me it was trying to deflect the reversion wave away from the exhaust port.

 

rotorbugg, congrats but I wouldn't use that exhaust. I agree with rotarygod about using a long primary instead. If only there was an easy way to install one in a bug...

 

I would think in the rotary you could combine the expansion chamber concept and the anti-reversion concept to good effect.

If you build an expansion chamber off your header collector that has a flat side in the front and then a smooth transition into your larger than collector diameter post expansion chamber exhaust it would seem to me this will function in several ways.

Anti-reversion- the flat front side and expanded volume will cause the bulk of the reversion wave to re-revert in the rear direction.

The turbulence of introducing the collector flow into the larger volume of the expansion chamber will provide an opportunity for external combustion (hint it has been found you can tune rich to amplify this effect).

Again, because of the flat front side of the expansion chamber and the larger than collector diameter rear exit the volume of expanded exhaust gas will favor the rearward direction.

By expanding the volume of the same mass of exhaust gas you have increased the velocity in the rear exit pipe.

The expansion chamber is now a pulsejet if you get the design correct and therefore the header collector is the pulsejet intake and has a lower pressure (scavenging).

Most racing classes will allow a sump breather or airpump connection to the exhaust. You can use this to introduce more combustion air into your pulsejet/expansion chamber using the collector as your venturi or you can have a strategically placed exhaust leak.

 

this is exactly what the stock sleeve/manifold does, although its setup for quiet and not performance.

my thinking is that since the stock manifold exit is sized nicely, it lets you just pick a normal muffler, or it lets you have an exhaust that is quiet, but flows enough that power isn't affected, at least at street HP levels

awesome! engine becomes pulse jet controller!