KA destroke?

[C-Kwik]

You should log in over at EFIU and ask in that thread. I'm sure you'd get your list, and it would make for some good reading. I'm inclined to believe those guys when they say "most of the engines produced today" when it comes to which one's achieve 100%+ VE. These guys are some of the top tuners in the world. They tune for a living, on a daily basis.

Also, to clarify something...the Enthalpy on that forum is NOT the Enthalpy that tunes Nissan ECU's. I asked.

Also, I never said that a VATN would be the only way to achieve the ideal pressure differential across the head. I was just stating that it would be a very good way to do so. It's not like the VATN is a BAD thing, right?

Modified by KATwo40 at 1:58 PM 4/19/2006

I would if I had more time. As it is, two or three forums are a handful already. The info I saw in that thread definitely shows a lot of knowledge, but consider that if they are tuners, they are going to be seeing motors that are more likely to see higher VE's. I doubt they are going to see your run of the mill motors of everyday cars.

Im a fan of the idea behind VATN turbos, but they've proven unreliable and can't handle high levels of boost.

[deviousKA]

Turbo charging an engine essentially raises VE, and that is how you work with it from a fueling and ignition standpoint. It not uncommon to tune up to 150, 180, 200% of calculated VE on a turbo car running speed-density, so as to work with it in a percent directly. You can easily obtain high VE (100%+) with a high exhaust pressure, that is a turbochargers favorite thing to do.

Calculated VE assumes constants either refined during r&d by input compared to displacement, which will require fine tuning before getting to that point (to get decent engine output), or by theoretical formulas that will provide exponential results across the board, at a minimum.

To accurately monitor/calculate the VE of your engine you would need standalone airflow monitoring equipment and a load dyno. Very very rarely does a tuner need to get this in-depth in monitoring an engine, and most that discuss their "VE" do not. It is extremely easy to be a true 5-10% off in your basic VE calculations,it doesnt matter unless if for direct comparison to another engine. Understanding how your VE is affected by changes is of the most importance, not the true value. Those methods save a lot of money on equipment, which would otherwise clean up ~5% of your values, of little true importance.

Exponential would be a good word to describe most speed-density or even maf tuning, with alpha-n your doing most of your work with TPS or just generally pulling your hair out and throwing things around.

Modern production engines usually run no more than 95% Ve, more commonly you will find 85-90% configurations. 100%+ even up to 120% Ve with a naturally aspirated racing engine is definitely possible, but like C-kwik mentioned, not something your commonly going to see on the street.

I would like to see one of these turbo applications where they are actually achieving higher intake pressure compared to exhaust and getting any true scavenging. That would be one highly engineered piece of equipment, damn good bearings id say, perpetual motion anyone?

[KATwo40]

Turbo charging an engine essentially raises VE, and that is how you work with it from a fueling and ignition standpoint. It not uncommon to tune up to 150, 180, 200% of calculated VE on a turbo car running speed-density, so as to work with it in a percent directly. You can easily obtain high VE (100%+) with a high exhaust pressure, that is a turbochargers favorite thing to do.

I understand the usage of the term VE in a fueling/timing standpoint. But in reference to actual VE, there's not a 200% increase by adding a turbo.

Just because 200% more air went through the MAF, doesn't mean that a 2.0L engine just consumed 4.0L in a combustion cycle. VE is relative to volume, not mass, right? Just like a shop air compressor, if you have the compressor empty, you have a 50gal. tank. Then, you turn on the compressor and fill the tank...still only a 50gal. tank.

It's as if you're saying that adding a turbocharger increases the actual displacement of the engine, which is not true.

Makes sense to me, anyhow, in my own little "mind garage"

[C-Kwik]

It really depends on whre you measure VE. Ignoring scavanging effects from a tuned system or restrictions placed on a sytem by outside forces(turbo) VE measures how well a cylinder is filled. So if you add boost to a motor, the VE doesn't change. The same volume enters the cylinders. The difference is the air going in is denser. The overall VE of the entire system will be increased by the pressure ratio, but the VE of the motor remains the same. This is why trying to increase the engine VE of even a turbo motor is still beneficial.

Of course, one could argue an apples to oranges comparison by saying a tuned N/A system would be an unfair comparison as well. I for one feel a turbo provides a much greater advantage so I'll give the N/A motor the benefit of the doubt in this type of argument.

[deviousKA]

Volumetric efficiency of the engine itself does increase with pressure, by increasing the volume of air ingested over the theoretical 100% dictated solely by dimension.

All that 100% volumetric efficiency means is the engine is ingesting an equal amount of air to its physical displacement. All VE percentages above and below are in reference to this value. By turbocharging you are feeding the engine pressurized air, basically increasing "displacement" without changing dimensions of the rotating assembly. A turbocharged 1.8l engine can displace the same amount of air as a NA 5.0l engine, it all depends on where you are measuring the flow, that the pressure is equal.

How big of tank would that 50 gallon pressurized tank fill, before it equaled the pressure of the empty 50 gallon tank? Which tank can do more work and therefor more efficient?

edit: scratch that last analogy ^

I should have said " which tank can "displace" more air". The empty tank is already at 100%.

[im two techno]

geese guys just buy an SR stroke it to 2.2 and call it a night...

[KATwo40]

lol, or just buy a motor with more cylinders.

[Edub1]

I think there might be a mixup in the terms here.

Volumetric Efficiancy should be actual filling / theoretical max filling. It is safe to say that .00001 CFM would pass through a drinking straw more EFFICIANTLY than 100 CFM would. So in this sense efficiancy would decrease as volume increases. That might be what he means when he says VE decreases.

Most of us think of VE in terms of actual filling / [stock] theoretical max filling. In this case VE, or just call it filling, is > 100%

So, it is correct that actual filling increases over 100% of stock max with a turbo and it is also true that the work required to do so rises just a bit faster than does the actual filling. In other words it might take 110% more force to pack in 100% more air.

As for the KA, it tops at 97% VE at around 4700 RPMs if memory serves. As for N/A motors above 100%, I'd like to hear this from an engineer who designes motors for an actual car company. It might be possible, but my guess is that it is not anything appreciable.

[KATwo40]

So, it is correct that actual filling increases over 100% of stock max with a turbo...

How can this be? The turbo moves air in MASS, not Volume, which is why a turbo map is read in lb/min (mass) as opposed to cfm (volume).

Regardless of the mass, the volume is the same, which is the direct calculation of VE. So, again, since the resonant effects created by the engine design are negated by adding a turbocharger, the VE (actual volume of air) would drop.

[Nismo_Freak]

So if you add boost to a motor, the VE doesn't change

It does, because you are now introducing a restriction and variations in resonance tuning to the engine. It will always alter the VE of the engine in that manner, and you can almost always assume that postive intake manifold pressure aside the engine is less efficient.

[Edub1]

How can this be? The turbo moves air in MASS, not Volume, which is why a turbo map is read in lb/min (mass) as opposed to cfm (volume).

Regardless of the mass, the volume is the same, which is the direct calculation of VE. So, again, since the resonant effects created by the engine design are negated by adding a turbocharger, the VE (actual volume of air) would drop.

I'm not sure what you're looking at here. If you take a given volume of air, say 2L and you double the pressure, you reduce this volume to 1L. So, you have 2X the molecules of O2 filling your cylinder.

A motors VE reffers to how much air enters under 1 atm or 14.7 psi. A turbo at 1 atm of boost compresses the air and packs 2 volumes worth into one. So, you have 200% filling. BTW, you could also do the exact same thing by cutting the C temp of the air in half. In this case, you would have 1 atm of pressure but 2X the O2. Conversely, if your turbo puts out 2X the heat, you could increase pressure by 100% but still have the same number of O2 moles.

[KATwo40]

I'm not sure what you're looking at here. If you take a given volume of air, say 2L and you double the pressure, you reduce this volume to 1L. So, you have 2X the molecules of O2 filling your cylinder.

A motors VE reffers to how much air enters under 1 atm or 14.7 psi. A turbo at 1 atm of boost compresses the air and packs 2 volumes worth into one. So, you have 200% filling. BTW, you could also do the exact same thing by cutting the C temp of the air in half. In this case, you would have 1 atm of pressure but 2X the O2. Conversely, if your turbo puts out 2X the heat, you could increase pressure by 100% but still have the same number of O2 moles.

Regardless of temperature, pressure or mass, the volume displacement in the cylinders does not change.

5.0L of air passing through the MAF of a 2.0L engine doesn't mean that the engine's displacement just increased to 5.0L. The volume displacement is still 2.0L, but the air has been compressed is more dense. Density is irrelavent to volume.

Example: Fill two beakers with 50ml of water. In one beaker, drop an egg. In another beaker, drop a piece of lead, with the same exact dimensions as the egg. The volume displacement will be the same in both beakers, even though the lead had more mass than the egg.

Furthermore, density and pressure change with altitude and ambient air temperatures. Therefore, your theory would state that an engine's VE increases and decreases as you drive over the mountains.

[C-Kwik]

It does, because you are now introducing a restriction and variations in resonance tuning to the engine. It will always alter the VE of the engine in that manner, and you can almost always assume that postive intake manifold pressure aside the engine is less efficient.

"Ignoring scavanging effects from a tuned system or restrictions placed on a sytem by outside forces(turbo) VE measures how well a cylinder is filled."

I put a condition on my statement to try and clarify the point I was making.

As far as positive pressure, and keeping in mind the condition I stated, VE would not be affected by pressure changes. Think of it this way, is you were to go to a place with an ambient pressure of say....7.35 psi, you'ld have half the mass of air going into the motor, but by volume, the motor would still fill the same volume of air. The air would just be half as dense.

When boosting a motor, the motor doesn't know or care what the density is. A cylinder with 100cc volume of displacement with 90% VE will take in 90cc of air from the intake manifold. Volume is a measure of space. It has nothing to do with how dense the air in it is.

As far as boosted motors, if you measure at the motor (again, ignoring outside factors) there is no change in VE. But it you measure ahead of the turbo, then yes, the motor will be ingesting more volume from ambient air than it's N/A counterpart.

[deviousKA]

I would like to point out that what I have mentioned is in reference to engine volumetric efficiency, not overall efficiency of a turbocharged system. It is not possible to obtain over 100% efficiency with a turbo charger, notice perpetual motion reference above.

Engine VE not only happens to increase with boost, it is directly increased for very simple reasons as I stated earlier. If the ka24e VE were to never increase over 100%, there would be no need for larger than 270cc injectors, in any application. Also, for what reasons would we need airflow measuring devices originally designed for 3-6L displacement, to run them on our turbocharged 4cyl (and actually max them out, holy ****). VE definately increases with boost, essentially in a direct relationship.

Now, where you guys are getting confused, is with the turbocharger. Overall efficiency you are confusing with the engines "volumetric efficiency". Turbochargers will always require more exhaust pressure than pumping pressure they are providing, and thus their efficiency is low and the new bottle neck of the system. I assume there are turbos that can provide near 100% efficiency (not a turbo guy really, I dont know), but over 100% turbocharger efficiency (lower exhaust/pump pressure ratio) can never be achieved, there is no energy to provide it.

I dont know if you would reference this overall efficiency with the term "VE" as commonly denoted to the engine itself. I wouldnt discuss it that way as it no longer the discussion of your engine efficiency, but of the efficiency of your turbocharger itself. In this situation, not being able to calculate your displacement/capability accurately, you have no theoretical 100%, and must base all of your efficiency testing in a real time flow monitoring situation.

[KATwo40]

You guys are using the term VE incorrectly, or I'm understanding it too scientifically.

VE = VOLUME of air actually entering the cylinder, as opposed to the theoretical VOLUME of the cylinder. In otherwords, the actual cylinder capacity (it's calculated dimensions).

A 2.0L engine consumes 2.0L of mixture, period. So what if 5.0L of air traveled through the MAF? After compression, there's still only 2.0L (or less because of issues created by the turbocharger) of air in the cylinder.

While the volume going through the air inlet of the turbo was the equivalent of 5.0L of air, it was compressed to 2.0L of air. In reality, only the MASS of the air entering the cylinder has increased, not the volume.

I think the issue here is that the industry has accepted the loose usage of the term VE. VE is now used to described the airflow seen in the ECU via the sensor array, when actually VE is really the volume of air in the cylinders themselves, not the air intake.

At this point, I'll stop this discussion and agree to disagree.

[deviousKA]

Well, no, actually, KAtwo40, your using the term volumetric efficiency incorrectly.

And furthermore, I am the only one that has discussed it in proper context.

EFI works in reference to volumetric efficiency (speed density example). Monitoring the "pressure" of the intake charge (vacuum, atmospheric, or boost) will determine how much air has entered the cylinder on that cycle, based upon a theoretical 100% VE that assumes atmospheric pressure (~100kpa). Increasing pressure over 100Kpa directly increases volumetric efficiency of the engine, which can easily go to 200%.

"Volumetric efficiency (VE) is used to describe the amount of fuel/air in the cylinder in relation to regular atmospheric air. If the cylinder is filled with fuel/air at atmospheric pressure, then the engine is said to have 100% volumetric efficiency. On the other hand, super chargers and turbo chargers increase the pressure entering the cylinder, giving the engine a volumetric efficiency greater than 100%. However, if the cylinder is pulling in a vacuum, then the engine has less than 100% volumetric efficiency. Normally aspirated engines typically run anywhere between 80% and 100% VE. So now, when you read that a certain manifold and cam combination tested out to have a 95% VE, you will know that the higher the number, the more power the engine can produce. "

And you guys can continue to argue, or you can stop humping your turbocharger and realize there is an engine attached, VE is in direct reference to the ENGINE at ATMOSPHERIC pressure, nothing else There are other terms to describe overall turbocharger system efficiency, none have been used here.

[KATwo40]

Well, no, actually, KAtwo40, your using the term volumetric efficiency incorrectly.

And furthermore, I am the only one that has discussed it in proper context.

EFI works in reference to volumetric efficiency (speed density example). Monitoring the "pressure" of the intake charge (vacuum, atmospheric, or boost) will determine how much air has entered the cylinder on that cycle, based upon a theoretical 100% VE that assumes atmospheric pressure (~100kpa). Increasing pressure over 100Kpa directly increases volumetric efficiency of the engine, which can easily go to 200%.

"Volumetric efficiency (VE) is used to describe the amount of fuel/air in the cylinder in relation to regular atmospheric air. If the cylinder is filled with fuel/air at atmospheric pressure, then the engine is said to have 100% volumetric efficiency. On the other hand, super chargers and turbo chargers increase the pressure entering the cylinder, giving the engine a volumetric efficiency greater than 100%. However, if the cylinder is pulling in a vacuum, then the engine has less than 100% volumetric efficiency. Normally aspirated engines typically run anywhere between 80% and 100% VE. So now, when you read that a certain manifold and cam combination tested out to have a 95% VE, you will know that the higher the number, the more power the engine can produce. "

And you guys can continue to argue, or you can stop humping your turbocharger and realize there is an engine attached, VE is in direct reference to the ENGINE at ATMOSPHERIC pressure, nothing else There are other terms to describe overall turbocharger system efficiency, none have been used here.

Not that it's really worth discussing anymore, and this truly will be my last post on this subject, but...

Again, your example focuses on atmospheric pressure. Well, if your theory rings true, then the VE would change according to the weather (since atmospheric pressure changes occur every day) and with altitude.

No professionally written definition of VE I have ever read has mentioned anything about atmospheric pressure, including writings from Corky Bell, Wikipedia, Ben Strader, etc.

For example, what if an N/A engine achieving 97%VE was taken to a place that was far enough below sea level to achieve atmospheric absolute pressure of 19.7psi (which would be 5psi above current sea level atmospheric pressure). Does this engine now achieve more than 97% VE, since the air is pressurized beyond atmospheric at sea level? No. The amount of air (VOLUME...hence the term Volumetric Efficiency) entering the cylinder is still 97% of the calculated volume of that cylinder.

And one last example...

Fill a 1 cup measuring cup full with flour. Now, pack the flour together tightly and top off the cup with more flour.

Did you add more flour? Yes. Did the volume of the flour increase? NO. It's still 2 cups of flour. The pressure used to compress the flour had NO BEARING on VOLUME.

I venture to say that the term's definition is mislabeled, or misunderstood/improperly used, industry-wide. Much like the term "bi-monthy," which most people think means twice per month, but actually means every two months, it's just terminology.

Furthermore, the actual VE of the engine itself (cylinder capacity) is of little importance. Once the engine is assembled and running, it is what it is. All you can do is calibrate for the air it can pull, or be fed, regardless of the VE % numbers.

[deviousKA]

Again, your example focuses on atmospheric pressure. Well, if your theory rings true, then the VE would change according to the weather (since atmospheric pressure changes occur every day) and with altitude.

Quite correct, unless the efi system has barometric correction (2 map sensors) it will only reference atmospheric from first power-on pre-start. This will provide erroneous VE calculations if the weather or altitude changes during the drive.

For example, what if an N/A engine achieving 97%VE was taken to a place that was far enough below sea level to achieve atmospheric absolute pressure of 19.7psi (which would be 5psi above current sea level atmospheric pressure). Does this engine now achieve more than 97% VE, since the air is pressurized beyond atmospheric at sea level? No. The amount of air (VOLUME...hence the term Volumetric Efficiency) entering the cylinder is still 97% of the calculated volume of that cylinder

(speed density example) If you were to drive to that altitude from a higher altitude, without barometric correction and without restarting the car, the efi would interpret incorrect VE. If you were to restart the car, the map sensor would correctly calculate the adjusted atmospheric pressure. MAF systems do not suffer from these problems.

How can you say it is truly 2 cups of flour if not completely compacted? Otherwise, you actually have 1 1/2 cups with some air in between, in a 2 cup container. There is a relation between density and volume.

If your reading a book that is discussing volumetric efficiency with no mention of atmospheric pressure, well then the book is

[Edub1]

This is funny already. What is the point of this discussion?

I explained in a previous post that you guys are simply using the term differently. Volume has nothing to do with it. VE, as I understand it and as most people use it mean the following. Read this carefully and the argument will be over - I promise.

VE = (internal pressure / atmospheric pressure) X 100

Where VE = 100%, both internal and atmospheric pressure are the same.

If you increase atm pressure, internal pressure will increase perportionally and VE will not change - this is KATwo's point. HOWEVER, what most people mean when discussing VE is how much the internal pressure differs from NORMAL atmospheric pressure which is ~ 14.7psi at sea level at 20C if memory serves. Chemists reffer to this as "standard temprature & pressure"

So, the math - (29.4psi / 14.7psi) x 100 = 200% VE as most people use the term(stp). Theory asside, the cylinders are in fact filling to 200% normal capacity because they are under pressure.

Volume is not at all important. It is only a description of the space that is currently being occupied by a given number of molecules under a given temprature and pressure. The important thing is how many O2 molecules we have in this space. With forced induction you will have greater than 100% of the O2 molecules possible under STP. This is all that matters for our purposes. VE is concerned with how many molecules enter, not with space. If space were the determining factor, you couldn't have less than 100% VE either, as the cylinder never gets any smaller. So, 97% VE must mean a drop in pressure, which at STP means a drop in molecules.

If this is unclear to anybody, I suggest reading up on the gas laws.

Efficiancy of a turbo system, as it relates to thermodynamics, is another conversation.

I hope this helps.

[deviousKA]

A much more eloquent explanation, thanks edub.

[KATwo40]

This is funny already. What is the point of this discussion?

I explained in a previous post that you guys are simply using the term differently. Volume has nothing to do with it. VE, as I understand it and as most people use it mean the following. Read this carefully and the argument will be over - I promise.

VE = (internal pressure / atmospheric pressure) X 100

Where VE = 100%, both internal and atmospheric pressure are the same.

If you increase atm pressure, internal pressure will increase perportionally and VE will not change - this is KATwo's point. HOWEVER, what most people mean when discussing VE is how much the internal pressure differs from NORMAL atmospheric pressure which is ~ 14.7psi at sea level at 20C if memory serves. Chemists reffer to this as "standard temprature & pressure"

So, the math - (29.4psi / 14.7psi) x 100 = 200% VE as most people use the term(stp). Theory asside, the cylinders are in fact filling to 200% normal capacity because they are under pressure.

Volume is not at all important. It is only a description of the space that is currently being occupied by a given number of molecules under a given temprature and pressure. The important thing is how many O2 molecules we have in this space. With forced induction you will have greater than 100% of the O2 molecules possible under STP. This is all that matters for our purposes. VE is concerned with how many molecules enter, not with space. If space were the determining factor, you couldn't have less than 100% VE either, as the cylinder never gets any smaller. So, 97% VE must mean a drop in pressure, which at STP means a drop in molecules.

If this is unclear to anybody, I suggest reading up on the gas laws.

Efficiancy of a turbo system, as it relates to thermodynamics, is another conversation.

I hope this helps.

This makes sense to me. I respond well to in-depth definitions, not generalizations.

Thank you for taking the time to explain this fully. I really don't post what I post for the sake of arguing. I post what I post to learn, which has been accomplished.

Thanks again everyone for your help here. I must say, I've been way off before, maybe even moreso than now, but I can't remember when.

[Chuckdst]

So what does the destroked KA run like? I think it would be pretty rev happy if you were to use 86mm stroke and a rod stroke ratio of about 1.7. I would like to know if a set up like this would live at 8,000 RPM. My main concern would be crankshaft oiling. Has any one race prepped a 86mm or 92mm crank. I know there are a few of you that have some real world experience with destroking the KA (deviousKA, Thursday).

[C-Kwik]

I think the problem here is not an incorrect definition, but that some of you guys are trying to limit the definition of VE to one thing. There is a difference between VE measured with the ambient reference in front of the turbo and in the intake manifold. Ambient pressure measured in front of the turbo measures how well the ENTIRE motor with turbo ingests air. Measuring VE with manifold pressure used as the ambient pressure measures how well the motor by itself is ingesting air. In the big picture, true ambient pressure is important, but measuring the motor's VE is important and has a purpose. In terms of turbos, it's primary importance lies in choosing a turbo. It's part of the airflow calculation you need to try and determine how much air the motor will pass through it. Nowhere in this equation does it tell you to calculate VE including boost pressure. In fact it would be impossible to accurately calculate airflow unless you already knew the overall airflow with the turbo, in which case you wouldn't need to do the calculation. Both methods are used by engineers. Each measure slightly different things.

As far as intake vs exhaust pressure, it would appear on the surface that it would be impossible for intake pressure to be higher than exhaust pressure. This is quite far from the truth though. medium to large turbos with good efficiencies can and do this when efficiencies are high on both the compressor and turbine sides. Consider that turbos do not simply use only pressure to spin a turbo. The pressure differential across the turbone is a source of energy and also important as it provides a carrier for the heat. This heat is where much of the difference is made. As the hot air expands through the turbine it releases this heat energy in the form of high velocity gasses. This is where the heat energy wasted out of the exhaust is recovered and a reason why turbos can see huge gains with proper turbo sizing.