Combustion Contraption

Much has been made of the 'anti-reversion' chambers in popular headers, such as the hytech model. For those just hearing of the term for the first time, anti reversion chambers are chambers in the primary sections of the header designed to persuade the exhaust charge to not re-enter the engine. I think the reason you dont want this happening is quite obvious.

Porters such as MAX_CFM have mentioned incorporating anti-reversion techniques into cylinder head porting, and how these techniques play into the 'behavior' of the performance of the combo. Do the techniques differ on engines with a 6k rpm redline from one with a 10k rpm redline? Suppose you had 2 identical setups save for anti-reversionary techniques in the cylinder head. Suppose you did a back to back dyno, in what area's of the powerband would the differences be felt, and what exactly would they be?

I have an interesting picture from a book called 'Practical Gas Flow' that i accidentally left at work which details some interesting cylinder head work regarding to this subject. I'll post a scanned pic as soon as i get it back.

Tuesday Club

Very interesting....

Keep the info coming

sheepey

Good info to be learned. Good job guy

The Birdman

Interesting sir

slofu

provocative. i like.

i'd venture to say that since more rpm means more ex pulses in the same time frame, that there would be subtle, important differences focused mainly around the valvejob to minimize reversion for the targeted (higher) rpm range, similar to the details paid to increasing overall flow to support shifting tq to higher rpm to build/carry hp longer.

Larry @ Endyn has said that he prefers to use the vj on the intake to stagnate flow at lower valve lift to fight reversion, since he finds most reversion to occur within that (lift) range, and since he manages to find enough flow at higher lifts to compensate. (i know that he's currently messing with increasing lower-lift flow to utilize lower-lift cams to reduce pumping losses, though.)

IIRC, Brad hinted that he configures his heads to flow more at lower lifts, since most cam profiles dictate that the valves are at lower lifts for much longer than they are at higher ones, so perhaps his techniques are different.

if we're lucky, Brad, Larry, Dave Localio, Joe Alaniz, Tom Fujita, or some other porters might give us some hints, but we can't expect them to 'give up the farm,' as this is likely an essential area which separates great heads from mere good ones.

hybrid_vtec

in to learn a thing or two.

RMF

I have a question.Just when is this reversion taking place.I have made loads of boat headers and exhaust. And some with water coming out of the header right at the port.And I have never had one hydraulic.If there is reversion don't you think that water would work its way in ?You can run a car all the way under water and it won't go back up the exhaust.Until its not running.At what point is the exhaust valve open when nothing is coming out of it?Im pretty sure the valve is being followed up by a piston.
And I have NEVER in my life seen a set of headers WITH the chambers make more power than the same header without them.I don't recall ever seeing a Real fast car with them either.

WHITFIELD-TUNED

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RMF &raquo;</TD></TR><TR><TD CLASS="quote">I have a question.Just when is this reversion taking place.I have made loads of boat headers and exhaust. And some with water coming out of the header right at the port.And I have never had one hydraulic.If there is reversion don't you think that water would work its way in ?You can run a car all the way under water and it won't go back up the exhaust.Until its not running.At what point is the exhaust valve open when nothing is coming out of it?Im pretty sure the valve is being followed up by a piston.
And I have NEVER in my life seen a set of headers WITH the chambers make more power than the same header without them.I don't recall ever seeing a Real fast car with them either.</TD></TR></TABLE>randy skooled me in this area of thought along time ago and i stil feel the same way today ... in my opinion anti reversion chambers on a header are a waste of time as well as money

slofu

good point. it could be, however, that since air is more elastic, and exhaust not as homogeneous as water, it behaves differently.

i'd guess that reversion is most likely to occur at valve overlap when the throttle suddenly closes, so that the pressure in the cyl/chamber is lower than that in the header.

John has said that the chambers in his headers help clean the reverting charge when the pressure drops on backward flow inside (of the chambers); the 'dirt' isn't so easily suspended. i remember when Larry asked him if it wasn't just (or almost as) effective to just port the header flange. John seemed to think that the chambers were still worthwhile. he also said that he tested the same headers, one with the chambers, one without, on the same racecar, and that although the (same) engine made more hp without the chambers, in the blind test the driver managed to pull off consistently faster laps using the header with the chambers (he switched them back and forth for the test). now they might work better on some engines/configurations than others; i have no experience with them, but for the sake of this discussion i just thought that i'd post what i remember having read.

my buddy who builds offshore marine racing engines has said that he's seen some builds with more cam overlap draw water back through a considerable length of exhaust pipe, but it could also be that the pressure difference is never quite enough to actually draw water into the cylinders, e.g., even under decel the pulses might balance before they're strong enough to pull enough water, which is considerably heavier and denser than air or exhaust. also, at a certain point the water impeding the exhaust flow might cause the pulses to stack and compress so that they block the water's flow.

Black R

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RMF &raquo;</TD></TR><TR><TD CLASS="quote">I have a question.Just when is this reversion taking place.I have made loads of boat headers and exhaust. And some with water coming out of the header right at the port.And I have never had one hydraulic.If there is reversion don't you think that water would work its way in ?You can run a car all the way under water and it won't go back up the exhaust.Until its not running.At what point is the exhaust valve open when nothing is coming out of it?Im pretty sure the valve is being followed up by a piston.
And I have NEVER in my life seen a set of headers WITH the chambers make more power than the same header without them.I don't recall ever seeing a Real fast car with them either.</TD></TR></TABLE>


From my limited understanding of reversion, it isn't necessarily that the water from your boat would work it's way back up into the head, but rather that the "dirty" burned exhaust fumes might not fully escape from the combustion chamber. So the intake charge is now partially contaminated on the next stroke and you aren't getting as much power due to this (less oxygen in the burned exhaust gasses).

From what I recall, Fueling used this theory on airplane engines a long time ago - and they operated at a much lower rpm than honda motors do.

That being said, it seems that anti-reversion doesn't affect WOT much (if at all) where headers are concerned. BUT they do affect the response of the motor between shifts, so in jumping from 9k back to 6k rpm on a 1/2, and 2/3, and 3/4, and 4/5 shift, the motor has some attributes to deal with in terms of deceleration and then acceleration again. This can play a very important role in drag racing and/ or lap times (I'm more concerned with the latter).

I believe John Grudynski addressed this issue before.

The bottom line (what I got out of it) is that for on/ off throttle type of driving, the anti-reversion chambers can and do make a difference in lap times.

Now we can go on about the theory of why..... *shrug*

drdisco69

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slofu &raquo;</TD></TR><TR><TD CLASS="quote">i'd guess that reversion is most likely to occur at valve overlap when the throttle suddenly closes</TD></TR></TABLE>

If you close the throttle, of course you're not going to make any power. No header in the world can help you. That's not the situation to be concerned with...

Combustion Contraption

I was always led to believe the A-R chambers were there to accomodate a broad powerband. I also realize, like RMF, ive never seen a real fast car (10's, 9's) with these chambers in use. Perhaps thats because of the limited RPM range they operate at.

What BlackR is talking about sounds alot like transient response to me, and while that is a great topic to discuss/debate, i have a feeling that would be a whole 'nother thread in itself.

slofu

many drag racers don't even lift off of the gas while shifting, so i'd say that for drag it's very possible that they make little, if any, measurable difference at all.

surely the airplane engines for which the AR chambers were designed, and in which they were used (long before Fueling was born, let alone patented them), operate under different conditions than our engines. however, most turbo development is done by/for diesel engine mfgs, and those diesels likely share far less in common with our engines than the old 5 cyl radial airplane deals. we manage to use turbos on our cars (well, not so much in the NA forum, but...), so it could be that the AR chambers May benefit Some of our setups in Some applications.

back on topic, though; the original topic was measures taken in the head to fight reversion.

slofu

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drdisco69 &raquo;</TD></TR><TR><TD CLASS="quote">If you close the throttle, of course you're not going to make any power. No header in the world can help you. That's not the situation to be concerned with...</TD></TR></TABLE>

but when you reopen it, if there's unburnt **** leftover in the chamber from the last cycle (which will not burn), it not only occupies space which good, clean a/f could use, it makes the new stuff harder to burn, which can effect the next charge, etc., so you can't burn as much fuel, spoiling efficiency (power).

DonF

The only people with enough R&D money to dyno with every set of headers- exhaust, are NASCAR, Champ-car, IRL, F-1, and the top NHRA people. If anyone can show a pic. with anti-reversion headers on any of those I would like to see them. NASCAR runs road courses as well as short ovals, so does Champ-car, one is NA the other Turbo, would like to see some pics of the anti-reversion stuff.

Combustion Contraption

Do you mean NASCAR, F1, Champ anti-reversion stuff, or just some pictures of it in general? Like hytech's design?

JohnnieChimpo

I don't claim to know how to fix reversion but I have experienced it.

My first motorcycle was a '87 750cc Ninja. I put a Muzzy free flowing exhaust on it and tuned the carbs on it. It ran pretty nice. Wanting more power I removed the restrictive air box and put 4 tiny KnN filters on it and re-jetted the carbs to Dynojet's specs. Ran great up at 11k but between 4000 and 5000 there was a a huge hole in power. I adjusted everything I could, different jets, different spark timing nothing. I called Dynojet they said I might have to adjust the cam overlap which at the time didn't sound fun. I took it to tuning shops who said they wouldn't even try to fix it because they've never been able to make them work.

Anyhow while tuning it once, I jumped on it in shorts and went for a ride up a hill to get it in its bad range and the hill would keep it there. While climbing, the sound of the engine changed once in the zone and my legs actually got wet with fuel as air traveled backwards through the engine on a reversion wave.

After that I did some reading and realized there was more going on inside an engine than I knew. Besides crank, rods, pistons, air/ fuel goes in exhaust comes out, there are things called pressure waves in the intake and exhaust that are affected by runner lenghts and diameters on both sides of an engine. When these lengths and diameters are properly tuned they can add power but when unchecked can result in tuning nightmares.

DonF

Pics of NASCAR, Champ-car, or NHRA using anti-reversion headers, I allready know what the the Fueling chambers look like. Even talked to him about them. I even know what the Mickey Thompson ones looked like at the head, plus his orig. tri-y's.

Ekasey

You wont find any Don We supply to a few of those orginaztions and i speak with lots of engine builders and everytime i speak with them reversion and how to cure it is never the topic of the subject.

I believe I have heard some things that came from Jim fueling himself that reversion is not a problem in modern day engines. However I can see it working on a airplane due to the slow operating conditons there placed in and how unoptimized they are for power

DonF

Casey, you must be over 25, seen real R&D and all that stuff, what do you think the power gain on BLUE neon lights is.

drdisco69

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slofu &raquo;</TD></TR><TR><TD CLASS="quote">but when you reopen it, if there's unburnt **** leftover in the chamber from the last cycle (which will not burn</TD></TR></TABLE>

By the time you get your foot to the floor, you'll have "clean" air and fuel in the cylinders. Engines are faster than you.

Everyone keeps talking about 9000rpm and all that fun drag racing stuff, but reversion usually rears it's head at the opposite end of the spectrum, when velocity (and kinetic energy) of the gas in the exhaust (and intake) ports is at it's lowest, and it's easiest to turn the air around.

DonF

So you agree they may work at 3000 RPM?

MAX_CFM

OMG your all so lost

The Birdman

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MAX_CFM &raquo;</TD></TR><TR><TD CLASS="quote">OMG your all so lost </TD></TR></TABLE>

haha. Great input Brad


Modified by jd3jdm at 12:58 AM 1/25/2006

Combustion Contraption

Yeah, agreed.