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iTrader: (2)

I haven't really seen too much discussion on this subject, i know for an NA car anti reversion chambers are important yadda yadda, just wondering if the same type of principles apply with a forced induction, specifically a turbo car...

i'm assuming no, just cuz i havent noticed it incorporated into the more popular manifolds everyone seems to be bandwagonning on these days...

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iTrader: (2)

?

Finest

One reason I would think that no one's used anti-reversion chambers is because in a FI setup, the exhaust flow is much greater than in an N/A setup. Flow and output is the key in any FI setup.

N/A requires a delicate balance of flow, yet still needs some backpressure to help scavage the last few remaining exhaust and inhale a fresh breath of clean air/fuel mixture. The anti-reversion chambers help by preventing the spent gases from entering back into the combustion chambers. FI motors are constantly expelling gas every which way due to a huge fan located in front of the exhaust ports. So the focus should be placed more on FLOW and OUTPUT to help spool up that turbo.

Hope that helps? Any other thoughts?

b18cls1

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Finest &raquo;</TD></TR><TR><TD CLASS="quote"> So the focus should be placed more on FLOW and OUTPUT to help spool up that turbo.

Hope that helps? Any other thoughts?</TD></TR></TABLE>

flow is really not waht spools the turbo it is actually heat that spools the turbo.the more heat the faster the spool thats why you wrap or jethot a manifold to keep the heat inside the manifold to help spool the turbo faster.

MachAF

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Finest &raquo;</TD></TR><TR><TD CLASS="quote">
N/A requires a delicate balance of flow, yet still needs some backpressure to help scavage the last few remaining exhaust and inhale a fresh breath of clean air/fuel mixture. The anti-reversion chambers help by preventing the spent gases from entering back into the combustion chambers. FI motors are constantly expelling gas every which way due to a huge fan located in front of the exhaust ports. So the focus should be placed more on FLOW and OUTPUT to help spool up that turbo.

Hope that helps? Any other thoughts?</TD></TR></TABLE>

N/A does not need backpressure. I don't understand why people are still thinking back pressure is good. How does back pressure increase mass air flow/velocity in ANY way?

Backpressure decreases peak torque. The only time backpressure has been any good in a 4 cycle engine is at low rpms, when there is excessive valve timing which stops the scavenging of the cylinder.

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iTrader: (2)

any fluid dynamics and mech eng's have any input on this matter?

where is ricehornet when I need him

I'm a business marketing major so this isn't really my field of expertise, in my lowly opinion i'd assume even if its an FI setup, exhaust gas leaving the head still has the same characteristics, even with the turbo.. does the turbo actually PULL air towards it, or does it not have an effect until the exhaust actually makes contact w/ the blades of the turbine?

Nid Styles

It would really depend on the setup to whether anti-reversion would be a positive, or just a waste of time.

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iTrader: (2)

hmm ok, what factors would determine whether anti reversion chambers are necessary, or would be a waste of time?

to me, its a manifold channeling exhaust gas to the turbo then out the DP... how else could it be setup ?

boosted hybrid

Full race geoff and I performed some testing between an equal length manifold vs log manifold. Interestingly enough the test completely contradicts what is perceived about equal length and log manifolds. Test results will be posted once geoff gets back from HI. Anti-reversion is a real concept, even with an FI application. Clearing residual burn in the combustion chamber will always yield power gains from having more available oxygen content to burn. Anti-reversion chambers can only aid in clearing residual burn.


Modified by boosted hybrid at 1:38 PM 7/5/2004

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iTrader: (2)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">Full race geoff and I performed some testing between an equal length manifold vs log manifold. Interestingly enough the test completely contradicts what is perceived about equal length and log manifolds. Test results will be posted once geoff gets back from HI. Anti-reversion is a real concept, even with an FI application. Clearing residual burn in the combustion chamber will always yield power gains from having more available oxygen content to burn. Anti-reversion chambers can only aid in clearing residual burn.


Modified by boosted hybrid at 1:38 PM 7/5/2004</TD></TR></TABLE>

more hype dispelled huh

Is this something that's never been considered/thought of w/ FI applications, or are people too lazy to incorporate it into their manifolds, or ???

can i get a spoiler on the results

btw u have pm

Joseph Davis

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Finest &raquo;</TD></TR><TR><TD CLASS="quote">One reason I would think that no one's used anti-reversion chambers is because in a FI setup, the exhaust flow is much greater than in an N/A setup. Flow and output is the key in any FI setup.</TD></TR></TABLE>

Since what you are dealing with when trying to promote scavenging is "forward" flow despite higher exhaust side pressures - part of that is reducing exhaust side pressures - then it only follows that scavenging on a turbo setup with a big fat turbine restricting exhaust flow is only 1000 times more important than scavenging on a naturally asphyxiated engine.

Wait, no, that came out wrong. What I meant to say is there is no difference between "naturally asphyxiated" and "farced induction." Pay attention to temperatures and pressures on both sides of the engine - and in the middle!
- and oddly enough it all adheres to the same exact principles, theory, and empirical reality. Turdbo is just NA with a higher intake pressure and temp (unless you're savvy)... and a higher exhaust pressure (and temp... unless )


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">Full race geoff and I performed some testing between an equal length manifold vs log manifold. Interestingly enough the test completely contradicts what is perceived about equal length and log manifolds. Test results will be posted once geoff gets back from HI. Anti-reversion is a real concept, even with an FI application. Clearing residual burn in the combustion chamber will always yield power gains from having more available oxygen content to burn. </TD></TR></TABLE>

Hrm, if you tell me anything that Bucci or Birdman didn't already know sixty years ago I will Paypal you the sum of one US Dollar.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">Anti-reversion chambers can only aid in clearing residual burn. </TD></TR></TABLE>

Only as a band-aid to poor manifold design and - this part is arguable - crap cam profiles... as in, every Honda stock or turbo cam profile currently out there.

I don't mean that as a mockery aimed towards you, Jeff, I really do respect the things you do. I'm just super-wierd, you know

beepy

I understand that the more efficient the exhaust is, the more efficient the turbo and thus the more efficient the engine.

But for the portion of the exhaust leading up to the turbine, is efficiency really that important? It is in a N/A engine, for good reason: The scavenging effect not only removes the exhaust gasses, but due to cam overlap it helps the intake gasses start filling the cylinders. In a F/I engine, you don't have to worry about this little "push", because you have a lot more pressure on the other side of those intake valves.

Thus, I would think that the header should be free-flowing, with enough effort put into tuning to simply avoid eddy currents as much as possible, and let the turbo do the rest.

But I don't know. Just making conversation.

Joseph Davis

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by beepy &raquo;</TD></TR><TR><TD CLASS="quote">The scavenging effect not only removes the exhaust gasses, but due to cam overlap it helps the intake gasses start filling the cylinders. In a F/I engine, you don't have to worry about this little "push", because you have a lot more pressure on the other side of those intake valves.</TD></TR></TABLE>

Nope. 99% of the turdbo setups on Honda-Tech have significantly higher turbine inlet pressure than intake manifold pressure.

pngfolife

Who is to say that anti-reversion chambers work regardless of the setup, NA or FI? NASCAR engines have volumetric efficiencies of over 100% without such exhaust work. The biggest challenge is tuning exhaust systems to get exhaust gas pressure waves to coincide with valve overlap.

Equal length headers or manifolds are desinged with resonant tuning in mind. They should be at least four times stroke length prior to merging in order to prevent cylinders pressurizing each other. This is of course for NA engines. 4x stroke length on a turbo car would cause problems since the exhaust would have lost much of its energy be the time it reaches the turbo. If tuned properly, reversion should not be present but on tubular manifold designs that do not have enough length to prevent cross-pressurization, "anti-reversion" chambers may be helpful.

Backpressure is essential for the operation of the turbo. It is not the heat that does the work on the turbine. By the time that the exhaust gas has reached the turbine, it is no longer a rapidly expanding gas (unless you are running extremely retared ignition timing). At this point, the exhaust has a great deal of kinetik, energy already. The gas transfers some of its kinetic energy when it hits the blades of the turbine. The pressure differential between the inlet and outlet sides of the turbo is what drives the gas in the proper direction. You want high pressure in the manifold and before the turbo and low pressure after the turbo which is why turbo-back exhausts help spool-up and peak power. These systems allow near maximum mass flow rates through the engine.

pngfolife

Sorry J. Davis, I don't have access to IMing since I'm still a trial user.

4x stroke length or longer (18" as you say) would be ideal but, might place the turbo too far from the ports and would delay spool at lower RPM. An easy way to correct this would be to use a BB turbo. If less kinetik energy is present, compensate by using a compressor that requires less energy.

Joseph Davis

As I said in IM, you haven't seen some of the tubies used in Hondas. The ~14.x" primaries your theory dictates for a GSR or LS are nothing compaed to what is used in the current aftermarket. Turbos are mainly driven off of exhaust flow, and the expanding of hot exhaust gases is what develops this flow.

Also, if you are using a properly designed tubular manifold (which is not a casting, or one of those schedule 40 heatsinks), it will be of thin gauge pipe. Thin gauge is ideal; it heat soaks in a flash (doesn't rob significant exhaust energy) and by it's very nature cannot bleed off enough heat into the open air, once heat soaked, to amount to a hill of beans.

BTW, where did you get the idea of 4X longer than your stroke? The whole idea of long runner tubular harmonics is to make the runner long enough that exhaust pulses don't bounce back from the turbine to the exhaust valve while it is still open. A cursory understanding of harmonics makes me wonder wtf stroke has to do with it.

Sunrise City Rider

Designing a manifold that effectively maximizes the velocity of the exhaust pulses is always a plus when designing a manifold, Turbo or N/A...Now, in a street car, you will have limited room to design such a manifold...Everything is possible but you always have to look at the whole picture...Usability, Durability, Worth of the Gains, and Cost will have the final say...

It has nothing to do with people being lazy...

pngfolife

It is not the expansion of hot gases that primarily drives the turbine, the majority of the energy extracted by the turbine is from mass flow. If expansion takes place within the turbine, the engine would make no power since the expansion of the gas is what drives the piston down on the pwer stroke. Ignition timing plays a huge role in this of course and late ignition will cause combustion to continue after the exhaust makes it into the manifold.

Thin gauge=good performance but prone to crack. In this case, bracing, high nickel alloy, and a titanium exhaust go a long way.

4x stroke length or longer. I never said the primary length has to be exactly 4x stroke length. Stroke length x4 is the ideal minimum. The reason you want the primaries at least this long I already stated. If the primaries are any shorter, exhaust from one cylinder will be able to pressurize other cylinders during their overlap phases.

Joseph Davis

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pngfolife &raquo;</TD></TR><TR><TD CLASS="quote">Thin gauge=good performance but prone to crack. In this case, bracing, high nickel alloy, and a titanium exhaust go a long way.</TD></TR></TABLE>

No, wrong. The 304 and 316 schedule 40 alloys commonly used for the Honduh tubies are ill-suited for the high heat ranges they see - peak EGTs fall at/outside their intended heat ranges. Also, thick wall tubing is prone to cracking, crystallization of the weld. A thin wall 321 SS manifold has none of these problems.

If you are looking at an SSAC manifold to form the conclusions, you are unaware of the salient facts: 1) tubies, thin wall or thick, are not meant to be used without bracing 2) SSAC uses cheap **** materials 3) SSAC is chrome plated which results in hydrogen metal embrittlement.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pngfolife &raquo;</TD></TR><TR><TD CLASS="quote">4x stroke length or longer. I never said the primary length has to be exactly 4x stroke length. Stroke length x4 is the ideal minimum.</TD></TR></TABLE>

I was never questioning the exactness of the 4X claim, I was questioning wtf stroke has to due with the harmonics of a tube with relation to exhaust pulse frequency.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pngfolife &raquo;</TD></TR><TR><TD CLASS="quote">The reason you want the primaries at least this long I already stated. If the primaries are any shorter, exhaust from one cylinder will be able to pressurize other cylinders during their overlap phases.</TD></TR></TABLE>

Uh, no. That is Bucci manifold design, and cannot be applied to manifolds consisting of more than three runners as you cannot avoid overlap with a higher number of runners tied together.

Birdman's manifold design was for long runner setups, where overlap was rendered irrelevant due to tube length and diamter. Exhaust pulses echo/bounce back when they hit the turbine, the long runner ensures the originating exhaust valve is closed before said pulse can return to it's originating cylinder and induce reversion. The larger diameter also reduces harmonic potency.

All this is aside from the fact, and rendered crap theory, by the fact that Hondas sidestep detonation and make such killer power BECAUSE of valve overlap (and about four other reasons I could name offhand in comparison to tradition turbo engines). They REQUIRE overlap.

pngfolife

321 stainless does perform best in the 450C-900C range but has higher high-temp strength due to the assition of titanium which isn't present in say 304. Nickel content is the same as 304 at 9%-12% though. Any manifold, tubular or log-style, are prone to crack is the total, both thermal and mechanical, stresses are beyond what the material can take. An interesting note about 321 SS is that it may form sigma phase which causes room temperature embrittlement, something that 304 will not undergo. So, 304 may crack under high thermal/mechanical stress but 321 may end up cracking upon cooling to room temperature if the mechanical stress is high enough.

Stroke has nothing to do with exhaust harmonics, 4x stroke length is the minimum length needed to prevent cylinders from pressurizing one another. The runners should be longer and equal in length for the best resonant tuning. Obviously, the major variable in determining runner length and diameter are EGT, cylinder displacement, desired RPM for peak power, and exhaust valve opening point.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote">
Uh, no. That is Bucci manifold design, and cannot be applied to manifolds consisting of more than three runners as you cannot avoid overlap with a higher number of runners tied together.

Birdman's manifold design was for long runner setups, where overlap was rendered irrelevant due to tube length and diamter.</TD></TR></TABLE>

I just said this above. "Long runner" meaning &gt;4x stroke length.

I believe that Honda engines "sidestep" detonation due to their superior combustion chamber design. Why else do they need such little timing advance (in NA form) as compared to most high performance domestic engines?

True, all engines require overlap, but excessive overlap is undesireable on a turbocharged car unless pressure reversion can somehow be prevented aside from cam timing. If the manifold design is correctly tuned, one can take advantage of a cam with more overlap since reversion is not a problem and can consequently see greater VE at equal boost levels. Which, getting back to the subject at hand, is why reversion chambers may be a very effective and inexpensive way of improving performance on turbocharged cars as well as NA cars!

shadow103rd

I would definitely like to see what a manifold looks like with these chambers incorporated into the manifold design.....It sould like it could possibly yield some positive effects in a turbocharged car.

Jon

Joseph Davis

Wow, so you agree with me that tubies need to be braced, huh?

I keep asking you to defend that point. I fail to see how stroke has any relation to runner length with so many other vairables at play.

No, what you said was:

It's not the other cylinders you worry about - you can't help the fact an exhaust pulse comes back up the runner, period. You just worry about timing things so that the exhaust pulse isn't timed well enough to cause reversion, such as during low combustion chamber pressures right before the originating exhaust valve closes.


Uh, yeah. A whole family of engines with poor quench, even the GSR which actually has quench still doesn't have enough. Frankly, there are other heads in the Honda family as well as in other OEMs with equal or better combustion chambers. B-series VTEC are the ones getting 450+ whp off pump gas, step back and look at how those engines do things differently. While it all takes place in the combustion chamber, it's not the combustion chamber that has the mojo.
A good working knowledge of what influences detonation would help you figure out half of it.

Bore diameter has a direct effect on ideal ignition advance, as the rate of burn across the cylinder must suit engine speed. Most domestics have a much wider bore, and so run more advance to achieve more time to burn fuel. Why else do the Honda engines need so little timing advance (in NA form) as compared to most high performance domestic engines?


All the fancy speak aside, we can all agree with that.

I've got one at the shop, I'll try to snap some pictures before the end of the weekend. It's a big fat bag of snakes 321 SS dealio.

pngfolife

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote">
It's not the other cylinders you worry about - you can't help the fact an exhaust pulse comes back up the runner, period. You just worry about timing things so that the exhaust pulse isn't timed well enough to cause reversion, such as during low combustion chamber pressures right before the originating exhaust valve closes.</TD></TR></TABLE>

You just answered your own question. If the runners are shorter than 4x stroke length, they will allow pressure reversion.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote">Uh, yeah. A whole family of engines with poor quench, even the GSR which actually has quench still doesn't have enough. Frankly, there are other heads in the Honda family as well as in other OEMs with equal or better combustion chambers. B-series VTEC are the ones getting 450+ whp off pump gas, step back and look at how those engines do things differently. While it all takes place in the combustion chamber, it's not the combustion chamber that has the mojo.
A good working knowledge of what influences detonation would help you figure out half of it.</TD></TR></TABLE>

So explain what the B-series VTEC motors are doing differently to achieve 450+ whp on pump gas.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote">Bore diameter has a direct effect on ideal ignition advance, as the rate of burn across the cylinder must suit engine speed. Most domestics have a much wider bore, and so run more advance to achieve more time to burn fuel. Why else do the Honda engines need so little timing advance (in NA form) as compared to most high performance domestic engines?</TD></TR></TABLE>

What about domestic 4 cylinders, ARC neons and the like? Honda engines run a great deal less spark advance even when reving 1k-2k RPM higher than the next Zetec motor or whatever. You have to admit that Honda did their homework when it comes to head design.

Joseph Davis

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

You just answered your own question. If the runners are shorter than 4x stroke length, they will allow pressure reversion.</TD></TR></TABLE>

No, I didn't. I corrected your incorrect statement about reversion happening in other cylinders than the one that originates tgghe exhaust pulse in question. What I am waiting for is your reasoning behind what 4X engine stroke has to do with anything

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pngfolife &raquo;</TD></TR><TR><TD CLASS="quote">So explain what the B-series VTEC motors are doing differently to achieve 450+ whp on pump gas.</TD></TR></TABLE>

There are three factors that most directly influence detonation - heat, time, and octane. Introducing the bulk of their flow past the engine's NA torque peak, which is where detonation is most prevalent. This goes hand in hand with "laggy" high rpm boost, where the engine is operating at a very high rpm when it makes power. Quite simply, you don't give the engine time to detonate with the high rpms and high piston speeds; and your powerlimit is more directly related to RS and rpms you can run. Laggy, big compressors also help control heat. Cam overlap in the upper revs helps valve/combustion chamber cooling, if you take pains to ensure there is no reversion to hold heat in the heat. The combustion chamber design you touched on is a factor in influencing mechanical octane - Honda chambers are good, yes, but only avergae as heads go currently. There is room for improvement

I could go on for a while.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pngfolife &raquo;</TD></TR><TR><TD CLASS="quote">What about domestic 4 cylinders, ARC neons and the like? Honda engines run a great deal less spark advance even when reving 1k-2k RPM higher than the next Zetec motor or whatever. You have to admit that Honda did their homework when it comes to head design.</TD></TR></TABLE>

Dunno about the ARC Neons, but the run of the mill Neon has an 87.5 mm bore - a bit bigger than normal Honduh. Clueless about Zetec; thought the USDM ones were 81mm, I dunno anything about the next incarnation. And, yeah, Honda heads are good, but we were talking about the combustion chambers alone

showtymers619

i like hondas specially when they are turbo how you all like dem apple juices