marcin

some poor guy is going to read the last half page and go out spreading it like gospel. because a bunch of heads on H-T said so.... It wont be me, but im just saying.

m.

2k.civic.si

theres already some much bs info on here why not?

marcin

was being funny
in regards to the muffler bearings, blinker fluid, etc.

m.

mike_belben@yahoo.com

at no point in an otto cycle engine's 720 degree cycle is a negative exhaust manifold pressure a bad thing. when present any time the exhaust valve is open, it is a great thing.

negative pressure, any negative pressure, IS "suction". any pressure lower than the current one will have a suction effect on a fluid as far as i am aware. the more negative it is, the greater the magnitude of "suction."

fluids flow from area of greatest concentration to area of least concentration. the exhaust valve opens prior to bottom dead center when chamber pressure is still quite high. a very high pressure blast is the driving force for most of the exhaust stoke's duration, called "blowdown." the exhaust manifold pressure will rise as the piston slows and the manifold's exhaust concentration increases due to restriction. if the chamber pressure is lower than the exhaust pressure at any time that the valve is obviously open, flow will reverse and fill the cylinder with exhaust gas. if the cylinder pressure is greater than the intake manifold pressure during overlap, the inert exhaust gasses will expand into the intake, then be reinducted after the exhaust valve closes and the pistons downward travel creates the pressure depression that draws the intake charge back in. the mixture now has patches of inert gasses that do not burn. this mix burns in layers, one at a time starting at the plug. if layer 3 is loaded with contaminants, layer 10 is not going to be burned as rapidly as it could have been without inert material. chamber pressure and temperates are lower, torque falls off. intake manifold design, to an extent can be used to compensate for reversion by ensuring a more positive pressure at the inlet valve during the overlap period than what is in the chamber.

i personally like to think of the blowdown (initial high pressure"poof" that comes out immediately when valve opens) as a comet. the head is thick while the tail tapers off. in a book i read, the head of the gas column is likened to a piston in an engine. it makes compression in front of it, and vaccuum behind it. this is the pressure that is used to manipulate the scavenging of adjoining cylinders through merge paired headers.

exhaust pulses travel at roughly the speed of sound, which varies somewhat with RPM, gas temp and pressure. (edit: thanks to luke for pointing out that intake is velocity dependant while exhaust speed is more "fixed.") while i am all for planning out a sweetspot, there is no tuned length that works perfectly everywhere. i think good results can be obtained using an exhaust that scavenges particularly well at one rpm and an intake that "supercharges" well at another, achieving a broad powerband.

i am not qualified to say i know which works or doesnt first hand, someday maybe. for now i can only piece together bits and pieces from the tests and experiments of others and form assumptions.

one thing i do know, sharp edges and abruptness make turbulence, and turbulence flows significantly slower than a laminar flow. not to imply that exhaust gas is laminar, i think the reynolds number is too high but am unsure. if the fluid flowing one direction sees a completely smooth path it should have little obstruction in that direction. if travelling in the opposite direction there IS an obstruction that creates turbulence, less mass of this gas should travel as far given the same amount of time than it would without the obstruction. i believe this is the idea behind anti-reversion chambers. i dont like the chambers as much as i like port extension into a larger primary tube at the flange.

so we know that there is no way to maintain a negative pressure at the valve at all RPMs and that flow reversal will occur. by placing this obstruction in the path of reverse flow, perhaps we can shear a percentage of the mass that would otherwise enter the chamber. if successful, the chamber will contain a lower percentage of contaminants. the burn rate will be increased and detonation resistance increased. having more room for fresh fuel is just icing on the cake. might it be a miniscule difference? certainly. so is the difference between going to the next round of eliminations or loading the trailor.

next time my little brother's digital camera is here ill try to snap some photos of pressure graphs broken down by crankshaft degree from some books.

when the clutch is disengaged the tire might as well be bolted to the crank. a fast car is one whos crankshaft has the ability to transition from a low RPM to a high RPM in a short amount of time, IE accelerate. i guarantee reversion hurts acceleration, and until i personally build/test several headers and see HP, TQ, BSFC and ET suffer, i am all for anti reversion devices.

hope this helps some of the newer guys.





Modified by mike_belben@yahoo.com at 12:39 AM 3/8/2005

00Red_SiR

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

at no point in an otto cycle engine's 720 degree cycle is a negative exhaust manifold pressure a bad thing. when present any time the exhaust valve is open, it is a great thing.

negative pressure, any negative pressure, IS "suction". any pressure lower than the current one will have a suction effect on a fluid as far as i am aware. the more negative it is, the greater the magnitude of "suction."

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

What you're talking about as negative pressure in the cylinder and exhaust manifold, and what I was talking about as a negative returning pressure wave are two totally different things. That being said I do agree with everything you said in your post, I'm just not sure if you misunderstood what I was saying in my post that you used for a quote.

mike_belben@yahoo.com

i agree that they are two seperate events entirely, but we will have to agree to disagree on whether the resonance pulses (low pressure waves) are beneficial. ive seen a good deal of indications that they are, and none that they are not. ofcoarse the world was once considered flat so im sure i have left room for error in the above.

i interpret your post to say that the negative returning waves force exhaust gas BACK into the cylinder even though the pulses gas density is lesser than the chamber psi.
i believe that the negative resonance pulse is more like a vaccuum cleaner knocking on the chamber's door. it appears all fluids seek equalibrium. i think this neg wave will travel only so far so fast until it meets the higher pressure and achieves equalibrium. someone mentioned that the negative pulse enters the chamber and creates a negative. that is something i am curious about,, i wonder if the negative pulse is of sufficient magnitude to "vaccuum" the chamber. as usual, more questions than answers is what im left with.

da'ee

Dave, are you going to build that header?

Black R

I do not proclaim to be an expert, and in fact I know that I don't know much...

That being said, let me also note that not everyone posts on honda-tech.
Hard to believe, I know.
But these days it seems like everybody's an expert.
Such an attitude can quickly dissuade many very knowledgable resources from posting here.
I got a quick email recently with regard to this subject from someone in the industry whom I would be proud to call a friend -
I'm not sure he posts here much if at all:

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Here is a picture of a Indy car header and F1 header.
If you look close there is a step in the pipe.
The pipe size is 2 inch into 2 1/2 inch.
At the step there is a ring that goes inside the pipe that transitions the 2 inch pipe to the 2 1/2 pipe.
That ring has a very sharp inner edge on it to reduce reversion.
I know because, I know the guy who makes the rings for the Indy cars.
These motors turn very high rpm's.
Some of the NASCAR teams also run the anti-reversion collectors so they do not tip off the competition to what they are doing.</TD></TR></TABLE>







Modified by Black R at 11:19 AM 3/17/2005

Ekasey

Ok well lets see here on the statements made above.....

To my knowledge NASCAR teams do not run anti reversion collectors, how do i know well we make a good majority of them. They may have at one time but currently i do not believe that is the case.

The INDY car header you spec'd has what most people refer to as the "big step"

That header actually looks to be howerton header, which most of these are spec'd out by the teams and built by that shop. I don't believe that the purpose of the "big step" is to provide an "anti reversion". I believe it is there becasue based on cam shaft bore stroke firing order etc. of the engine that is the tubing size that the engine likes. Therefore If you run 2 1/2" off of an extremely small port you are going to decrese velocity in the gas speed there fore hurting power. I belive the big step is also there to attentuate the negative reflected wave to the proper ammplitude, as to not promote a haeder that scavenges so hard it will make it difficult to get the engine to run right.

Fact of the matter is that you are not going to experience reversion in a motor that runs this high of RPM. If you are its probably at idle and no where else.

If i'm wrong and soembody can provide some solid proof that would be really damn cool

SMSP

"Some of the NASCAR teams also run the anti-reversion collectors so they do not tip off the competition to what they are doing."

Damn, now everyone knows about it!

RMF

I have your back on that one. Casey. I believe the same.But I have only been building headers for 30 years.On everything from gopeds to helicopters.But if you can sell those things, Good luck.Its like tune up in a can .I can't believe people really buy that crap.

ShaunRR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RMF &raquo;</TD></TR><TR><TD CLASS="quote">Its like tune up in a can </TD></TR></TABLE>

LOL

S2 INSIDER

voodoo mumbo jumbo....from what i understand, guys at skunk actually asked Fueling about AR chambers and even he laughed at the thought of it working on a an efficient high rpm engine....ironic that even the inventor, who probably forgot more than we know collectively, thought it was a worthless invention for our type of engines.....perhaps he died laughing at the very thought; rest his soul

from what i understand he didn't think to highly of hytech either. nor do the people that hytech <U>claims</U> to build toyota atlantic headers for.

i can't wait to read the responses of all the bench racing engineers in training

Combustion Contraption

Hey s2 insider, who are you exactly?

S2 INSIDER

i used to work at skunk as an engineer.

now i work with the tv show "overhaulin". but still keep in close contact with the people at skunk. i made alot of close friends during my time there and consider them family.

mike_belben@yahoo.com

why dont you shed some enlightening engineer knowledge instead of all these whispers youve got?

Combustion Contraption

Do you have a name s2 insider? Mines steve, for example...

2k.civic.si

"Some of the NASCAR teams also run the anti-reversion collectors so they do not tip off the competition to what they are doing."


right and you know of this how? the only people who would know this is the ones who actually work on the motor and build the parts and im sure they had to sign non-disclosure agreements for the equipment they work on....standard procedure for anyone in a competitive feild....

S2 INSIDER

john...its in my profile.

i happen to like whispering and living vicariously through others

S2 INSIDER

oh btw...i am not an IC engineer. and cannot speak intelligently about the effects of pressure waves, wave scavenging, blah blah blah. my design and engineering background lean towards general mechanics and vehicle dynamics

descartesfool

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR &raquo;</TD></TR><TR><TD CLASS="quote">Scott, who has almost lost interest in going faster with horsepower</TD></TR></TABLE>

That's sick!

You know it's not really true in your heart of hearts. I just took off my anti-reversion chambers yesterday. Looked kind of sad sitting on the floor all by themselves, banished to a dusty corner. I'll miss them, well maybe not too much, unless the evil god DNF rears his head to challenge the new god Garrett. Gotta have more Powaa!

Pressure, pressure, its all about pressure. Gotta bump up my BMEP's.