School Me: WAI vs CAI
 

Okay first let me say I know there are ton of wai vs cai threads but none of them seem to address new technologies and account for them. School me or provide your input on cai vs wai in the different applications.


This thread is only concerning mostly gasoline engines and applications.

Few definitions first:
Stoich:
The modern engine is trying to keep a 14.7 to 1 mass ratio of air to fuel.
Air

The Engine Control Unit (ECU) adjust air flow or fuel flow to meet this ratio as close as possible. This measurements are based on oxygen sensor, fuel pressure, and map/maf sensor. Stoich takes into account volume and oxygen readings.

Stoich ratios are achieved based on open and closed loop. Open loop means only the maf/map sensor is dictating ratios. Closed loops means the maf/map and oxygen sensors are dictating ratios.

Cold Air Intake (CAI):
A intake designed to draw cooler air from parts of the engine bay that are cooler than the factory design air intake draw air from. Often these are located near the bottom of the engine compartment where the air is not as hot.

Warm Air Intake (WAI):
A intake designed to draw warmer air from parts of the engine bay that are hotter than the factory design air intake draw air from. Often these are located near the top or exhaust of the engine compartment where the air is hotter.

MAF/MAP Sensor
MAF sensor: measures the amount of air flow in terms of volume. It does not measure the amount of oxygen entering the engine.
MAP sensor: measures the amount of air flow in terms of volume based on predetermined calculations based on air pressure/intake temps/etc. It is not exact or a direct approach like a MAF but it does not interfere with air flow and is cheaper to service/produce.

Conventional Throttle
A butterfly valve is controlled via a cable connected to the accelerator that driver physically controls.

Drive-by-wire
A butterfly valve is controlled by the ECU based on given parameters such as user accelerator input, gear, and engine readouts (rpm,air temp,etc).

DBW is able to improve efficiency by providing the optimal butterfly valve opening conditions. Downside is that it does not allow full direct control(sensors regulate the butterfly valve instead of a cable) for hyper-milers but is more efficient for the masses.

Butterfly-valve
A valve that opens and closes often inside the air intake to allow air to enter the engine.

Camshaft profile
The profile of the camshaft lobes that allow how far a valve opens or closes. Think "how wide"

Camshaft phasing
The phasing or adjust of the camshaft angle to allow for changes in duration that a valve is open or closed. Think "how long"

Valvetronic/VEL
BMW/Nissan designed actuators that allow for infinite camshaft profiles. This means the valves open as high or as low as they want based on engine conditions allowing. It eliminates the need for typical/old camshaft profile designs that are often bought by v8 grurus to increase horsepower.

This gives the engine ability to eliminate a butterfly valve completely since the valves can now control air intake. Throttle losses essentially become minimal and efficiency is increase in terms of MPG and Power.

Note: There is often still a butterfly valve present as a backup in-case the system fails so the car can be limped home but in normal operation it is always completely open.

Intake/Exhaust Variable Valve Timing
Intake and exhaust cam phasing is adjusted meaning retarded or advanced to allow for shorter or longer durations the valves are open or closed.


School Me Part/My Theories (Provide input or ideas on each part):

1. Theory CAI:
Colder dense air has more oxygen. The more oxygen the more powerful the combustion process is and more power is produced. In open loop Stoich, more air needed to meet the volume so it sucks in more air. More air and fuel is compacted in the combustion chamber but the same amount of fuel volume is still used so a slight fuel savings.
In closed loop Stoich (most cars), the ECU sees more oxygen so it adds more fuel to match stoich so more fuel is burnt and more power is created. A slight decrease in mpg but is negated by the fact the engine can run at a lower rpm and make the same amount of power thus a net slight increase in mpg and power.
The net effect is based more on engine applications and RPM speed to see a true increase in mpg but there is always a slight increase in HP.

2. Theory WAI:
Hotter dense air has less oxygen. The less oxygen means less power is made. In open loop stoich, there is too much air entering so the ecu decreases fuel to maintain stoich.
In closed loop stoich (most cars), the ECU sees it needs more oxygen so the butterfly opens more which results in more air volume and decrease fuel to also meet stoich. The results of the butterfly opening more is a decrease in throttle losses caused by back pressure created by vacuum and turbulence.
The net effect is throttle losses outweigh the power decrease and fuel economy improves more than CAI.

3. DBW improves throttle losses but they are still there with CAI. Basically same affect as conventional throttle just a slight efficiency increase.

4. Valvetronic/VEL reduces the need for a WAI because the warm intake strives to decrease throttle losses but since there is no butterfly valve or turbulence the WAI hurts the engine more than it helps. WAI only apply to DBW and conventional throttle vehicles but are a hindrance on new cars with infinite cam profiles. Car engineers don't put WAI on new cars since this holds true but some do put ram air ducts and cold air ducts to improve power.

Thanks for any input and ideas. I am curious to see others people theories on these concepts and any scientific experiments to prove them.

...since you seem to be asking about a BOSCH system, contact them.

ABA test both since WAI usually provides an MPG boost to gasoline engines, but not always.

If you have a diesel don't bother with WAI, unless its really cold.

You say that cold air has "more oxygen" and warm air has "less oxygen". That's sort of true. Cold air does have more oxygen per unit volume--but only because there's more air per unit volume. The temperature doesn't affect the percentage of oxygen in air--therefore the amount of oxygen per unit mass doesn't change.

Now, you might be tempeted to think that because the stoke of the engine is a fixed volume, that volume is what matters. However, closed loop control keeps the air-fuel ratio basically constant (near stoich)--and AFR is mass-based, not volume based--the throttle will adjust to keep the same mass of air regardless of temperature (by changing the intake pressure). So warmer temps mean higher intake pressures--to keep the density the same. Higher intake pressure means lower pumping losses and also lower throttle losses, therefore, better fuel efficiency.

Also, warmer air increases the flame speed, so the combusion happens more quickly, giving it more room to expand. That also increases fuel efficiency.


Diesels are a different story because they're typically not at constant AFR and also don't have flame propogation. I've gone into the details on how a CAI benefits a diesel in other threads, but since you asked about a gasser, I'll stop now.

Great explanation. I would only add that the hotter the intake charge at the point of injection, the better atomization of the fuel.

regards
Mech

No, for economy a modern engine will try to enable lean burn, where the A/F ratio might be up to 22:1, when conditions allow. Warmer intake air apparently increases the RPM/load range where this is possible.

Let me add that todays' modern engines try to maintain 14.7:1 mass air/fuel ratio, not for economy or power, but rather for EMISSIONS COMPLIANCE.

That's *why* individuals have to 'circumvent/trick' the engines normal "closed-loop" operational mode to make them "more efficient," by getting the ECM to operate closer to "lean" A/F ratio (16-18:1) than the 'chemical correct' stoichiometric (14.7:1) ratio needed for EPA requirements and catalytic converter "longivity."

Thanks for that explanation. It is hard to find a legit explanation that doesn't just say it "works because it works".

So the question comes down to new technologies now.

With infinite cam profiles the cam profile is optimized to virtually eliminate pumping losses. Since it is 99% optimized the need for a wai is basically negated besides the slight minimal increase in flame speed (DI helps with this more). A cai though is still beneficial. Thoughts on this?

Side Note: For other readers, pumping losses are inefficiencies caused by vacuum created when the valve closes causing air to back track within the intake system. The engine has to work a little harder to draw back in this air which are pumping losses. Back in the day car tuners would run intake runners which were designed to eliminate this back pressure. Some new cars still use this idea but use an extra butterfly valve to simulate intake runners.

Yes thanks for clarifying. I was aware of this already as I know stoich does fluctuate and sometimes other air fuel ratios are targeted but other readers will find this useful to know.

where to start
 

Stoich, is a ratio of fuel to oxygen that will allow fuel to ignite; now when it comes to modern engine controls; it depends on engine coolent temp, intake temp, map/maf, tps and o2.

most cold air intakes do not go down past the engine(because lower means water getting sucked up/hydrolocking/getting sued). "cold air" is subjective.

most engines from the 80 and earlier had some variation of this, to help with cold start issues(too much oxygen to fuel). Still questioning why they got away from thermac's for fuel injection.

the only maf i've seen that interferes with airflow is the spoon type that ford used in the late 80's/early 90's

MAF systems use the same sensors to calculate air flow as the map does, just uses a different way to determine fuel; it's also an indirect method.

nope, the camshaft profile is when it open's and how long it stays open per cycle.

LIFT is how far the valve opens and closes


Camshaft phasing is the change of camshaft timing in relation to it's static position; does not change duration

might want to read this

AutoZine Technical School


nope; duration doesn't change, phasing a cam changes when it opens and closes(eg crankshaft rotates 720 for every 360 of the camshaft; phasing means a camshaft the opens at 208 normally would move 10 or more degrees +/- so 208 could end up phased at 198 or 218 depending on the computer)

Schooled

Stoich, is a ratio of fuel to oxygen that will allow fuel to ignite; now when it comes to modern engine controls; it depends on engine coolent temp, intake temp, map/maf, tps and o2.


Partially correct: It is ratio of fuel to air. Air consists of oxygen yes, but also carbon and hydrogen. Air is not the same as pure oxygen. Read about open and closed loop for how an engine matches stoich or whatever AFR ratio it is targeting.


most cold air intakes do not go down past the engine(because lower means water getting sucked up/hydrolocking/getting sued). "cold air" is subjective.

Wrong: Actually they do, people put sleeves over them to prevent hydrolock. You might be thinking of a SRI short ram intake which is different from a CAI.



most engines from the 80 and earlier had some variation of this, to help with cold start issues(too much oxygen to fuel). Still questioning why they got away from thermac's for fuel injection.

True


the only maf i've seen that interferes with airflow is the spoon type that ford used in the late 80's/early 90's

MAF systems use the same sensors to calculate air flow as the map does, just uses a different way to determine fuel; it's also an indirect method.



Wrong: All maf sensors are in direct line of air flow and do cause interference. The air has to move through and around the maf sensor inside the air intake. There is a slight decrease in efficiency because of this but is more accurate for the ECU as real-time data is calculated instead of in direct like a map setup. A Map sensor measures manifold air pressure and not air flow. They are two different setups but do share some of the same sensors but they are different.



nope, the camshaft profile is when it open's and how long it stays open per cycle.
LIFT is how far the valve opens and closes

Wrong: camshaft profile controls how far the valve opens and closes, same thing as lift, not duration. It only hits the lobe once, for it to stay on the lobe the camshaft must be advance or retard which is what camshaft phasing is.


Camshaft phasing is the change of camshaft timing in relation to it's static position; does not change duration


Wrong: What do you think camshaft phasing does then? You just said it yourself it changes timing which is the definition of duration. You are getting your definitions confused between phasing and profile.


might want to read this

AutoZine Technical School

Cool article, but I already knew what it does/is. It might be helpful to other readers who want to see visuals.


nope; duration doesn't change, phasing a cam changes when it opens and closes(eg crankshaft rotates 720 for every 360 of the camshaft; phasing means a camshaft the opens at 208 normally would move 10 or more degrees +/- so 208 could end up phased at 198 or 218 depending on the computer)

Wrong: Once again you are contradicting yourself by saying duration doesn't change. Phasing a cam means the cam is able to maintain that lobe profile longer or shorter which is the definition of duration/timing.


Do you have any input/idea off a WAI on new techonlogies as the thread was intended?

air defined

love to know where the hydrogen is?

sri is a version of a "cold air" intake; and is what is most commonly refered to as a cold air intake; when in actuallity it sucks in ambient engine compartment air like the factory one.


i could be "wrong" here but i and everyone else defines "profile" as the curve that extends outward from the base circle, but in order to do that it controls more then just lift.
it also controls when it opens and closes which is duration.

where as cam phasing it the changing of when it happens in a 360 degrees of turn of the camshaft. case in point my previous example.

besides if "a follower" were to hit a cam it would bounce, not ride on it


ps. you already knew that yet you said it was cam-less; quite to the conterairy it has a cam it changes valve lift, not the "profile" as you like to call it

pss. we can continue this if you like; i think you don't know your definitions.

love to know where the hydrogen is?

It is called water vapor and it is always present in the atmosphere. The meteorologist like to call it "humidity". H2O.


sri is a version of a "cold air" intake; and is what is most commonly refered to as a cold air intake; when in actuallity it sucks in ambient engine compartment air like the factory one.

Exactly glad we agree on something. It is often easy to add dryer duct work to a SRI to get the effect of a wai



i could be "wrong" here but i and everyone else defines "profile" as the curve that extends outward from the base circle, but in order to do that it controls more then just lift.
it also controls when it opens and closes which is duration.


where as cam phasing it the changing of when it happens in a 360 degrees of turn of the camshaft. case in point my previous example.

We are just getting hung up on the details. It doesn't have anything to do with this thread. This is correct in what I/you were trying to explain.



Anyways I feel a wai intake advantage of throttle losses is negated with new valvetronic/valvematic/vel systems. A CAI is now more beneficial in terms of efficiency and power but only on these types of applications.

Its really going to differ from engine to engine. I suggest testing a few different intake configurations to see what really works for your engine.

If the engine comes from the factory with a low threshold for detonation (i.e. high compression ratio in most cases) then you should really think twice about WAI. Not only is there a possible large drop in performance, but your efficiency could go down.

Higher intake temperature = higher charge temperature. While this helps the flame speed, it also reduces the heat ratio of the charge and thus reduces the power extracted on the expansion stroke (as a proportion). It also puts more stress on the various engine components from higher pressure, aka more friction.

WAI is a very crude method of improving fuel economy, as it exploits a fundamental "design flaw" of most engines in a way that has negative effects on some aspects of efficiency.

With Valvetronic/etc. WAI is probably a bad idea because down to maybe 40% VE those engines should be running more efficient at less VE, and especially if they have high compression ratio such as the Nissan VQ37VHR engines.

Uh, ya lost me here.

I was under the impression that we had a throttle body which limited the amount air which would be let into the intake manifold, thus, a manifold vacuum, the amount of energy required to pull the air past the throttle plate is where the loss occurred. It takes power to draw in the air, the power comes from the engines, thus a loss. You can't tell me it is an effortless process to draw air across the throttle plate.

Your love affair with valve management systems is misplaced in my estimation, you have seriously confused 2 different processes going on in the engine.

Also, you claim hydrogen is present in the air due to the humidity that is "Always there". Here in the north, when temps drop low to freezing, there is very little to no water vapor in the air, at its most it's 4% with 2% being common on warm summer days most places. Understand however, this vapor does NOT contribute elemental hydrogen to the combustion equation since it is already attached to oxygen thus being water. It will be a factor on a small scale in its ability to remove heat & such, but the effect is tiny, and unless you're running a top fuel dragster, really isn't worth discussing.

Anyone else wanna talk these points through?

Older cars do have a throttle plate but these cars with these new infinite variable valve technologies are able to omit the throttle plate completely. Now when a driver pushes the accelerator the ECU tells the valves what to do and controls air flow this way. The air flow is control actually by the engine valves and not a throttle plate (talk about no control over engine input, the ECU is doing everything these days for the driver). There is no longer the restriction of a throttle plate which accounts for almost all of the throttle losses in a typical engine due to back pressure.

So maybe you are thinking there is still some throttle loss due to valves being closed when air is trying to enter the engine, but the ECU can time the valves precisely to open at the exact moment to minimize this effect. There might be a 1-2% of blockage which is why I say it is 99% efficient in eliminating throttle losses. Toyota seems to have the best design in terms of simplicity and weight of the system.

Here is a direct quote from an article someone posted, you can find this same information on other sites also:
"Moreover, car makers can make use of CVVL to regulate engine output, thus eliminate the need of throttle butterfly and reduce so called “pumping loss”"


You are correct about humidity but there is a small factor involved but not worth really mentioning on passenger cars but he asked so I provided.

So I was under the impression you were stating that a lot of cars driving on the road now all have CVVL systems in place which eliminate the throttle. This I contend is not quite the case, but it may not be long in coming.

I have to admit, I had a whole paragraph written up which was going to blast this whole CVVL as dreamland non-sense. Then, to make sure there wasn't really something to it, I Googled it. OK, I was really ignorant regarding these valve control methods. I have a VTEC Honda that I knew did some flibbity flu thing with the valves, but had no idea other car companies had gotten so far ahead.

I have revised the previous paragraph needless to say, since I'da looked quite troggish posting it.

OK, so I've read through some articles (find below) and educated myself on CVVL. I see it is mentioned that there is potential to eliminate the throttle, but, I don't see where anyone has done so completely yet.

I think that car makers want to get a few gazzilion miles under their belts running a CVVL with conventional throttle before they jump in whole hog on letting the CVVL thing take the entire load. I see BMW has a throttle for start up and backup to a Valvetronic failure (limp home), but does indeed open the throttle fully when the engine operates normally.

The main take away I'm getting from all this is that by closing the inlet valve before the piston reaches BDC (er... Bottom Dead Center) you can control the "charge" that way and thus eliminate pumping loss. It appears a small amount of "loss" is good in that it creates a healthy swirl to promote better combustion which off sets the loss and then some.

Interesting stuff, here, here, here, and here.
Notice - the red "here" is a big file if you have slow internet.

Thanks for bringing all this up. I learned a lot. It's one of the things I love about this Ecomodder family, it really gives us the opportunity to explore all things automotive keeping our minds sharp and growing.

SRI = short ram intake. Sometimes set up like a warm air intake. Its not a cold air intake at all but intakes air usually from directly beside the engine the shortest path. Not sure where the "RAM" part comes into play, probably more marketing than anything else. I have tested these and temperature variations fluctuate wildly as at rest it sucks up hot air radiating from the engine and radiator, then as one gets to speed it begins to fall.

CAI = cold air intake...obviously already covered. The object is not to intake air from air supply down lower than the engine, or any other altitude relation to the engine. It is intended to draw air temps as close to ambient air found outside the engine bay as possible. Often this means putting the intake end as far away from the engine as possible and where a filter will fit if an entire replacement set up is used. Consequently this often means putting the intake opening/filter behind the front bumper under the headlamp. temperature variations are minimal nearly constant as far as the intake tube/tract is heated by surrounding air. CAI Hydro-lock concerns are only realized when idiots roll through water that is deep enough to immerse the intake filter element and it sucks it up like a straw. For the rest of those that avoid water that is 12 inches deep or more as pure common sense, it is never an issue.

Interesting to know that there are quite a few CAI from factory, My 1997 Suburban has one, there are even some ram cold air intakes (which puts the cold air intake directly in the airflow like those found on the new Insight.

Some cars it makes little to no difference with regards to fuel economy whether CAI or WAI (SRI). There is some difference in power in some engines...which has been covered.

Thank for you for the added information and insight. My main purpose of this thread was to provide some education but also to spark ideas or new theories on how new intake designs differ in terms of efficiency on new technologies. I already know how wai/cai/sri work on regular old MFI but I was curious how they work on these new valvetrains and intake systems and if their affect still holds true.

My personal opinion is that WAI is no longer an mpg booster since the main reason it increased efficiency was that it was "tricking" the ecu to open the throttle plate more but now that throttle plates are a secondary/backup systems wai only has negative effects now. CAI and SRI are still effective keeping in mind same size and length of intake tubes whether if it is a sri, cai, or wai.

Just for clarifcation when I say WAI I mean HAI as some kind of duct/piping that is drawing in warm/hot temps from the engine bay into the air intake. I think of a SRI is just a short length tube with a filter and that is all. A wai is a sri or cai + tubing to the exhaust hot/warm air.

Valvetronic, Valvematic, and VVEL are capable of 100% throttle independent output control. The throttle is backup only. They can cut duration to under 20% maximum duration, which is enough to idle. Engines that do so need pumps and motors to drive traditionally vacuum boosted things.

The pumping loss that early intake valve closure induces is not so bad because the pressure drop happens at the valve, and the air at low pressure is contained completely within the cylinder and so a greater percentage of the initial power consumption drawing air past the restriction is recovered on the compression stroke. The bigger downside is probably that on the intake stroke as the charge is expanding, it absorbs more heat from the cylinder walls and thus incurs some more pumping loss, but I am not sure how big of a deal this is.

Joeggernaut, throttle by wire is not actually very different from cable throttle. Most engines are not equipped with any kind of variable lift system, and the only variable valve timing is cam phasing. The advantage that electronic throttle control allows is for the cam phasing system to work together with the throttle, rather than responding to a throttle input (and lagging behind, throwing away some of the efficiency benefits). However the amount of control that intake cam phasing has over volumetric efficiency is not nearly as good as Valvetronic. The range of positions for cam movement has been increasing, but retarding the opening of the intake much past TDC starts to incur significant pumping loss. As long as there is significant vacuum to deal with a warm air intake has the potential to improve fuel economy because throttling losses tend to be quite serious.

I read most of the articles Chaz posted. I don't think we can say variable lift technology 'virtually eliminates pumping losses'. It sounds like they've just moved the restriction from the throttle body to the intake valve. Something still has to control how much air gets in, and they're still using the intake valve as a restriction. Its definitely an improvement, but I just don't think we can say pumping losses are virtually eliminated. I think reduced is a much better word.

The only exception I can see is if they're using something similar to Toyota's atkinson-like cycle (used on the Prius/Camry hybrid) where the intake charge is partically exhausted out of the intake valve.

Say you had a variable lift system that controlled the rocker ratio rather than using a secondary rocker to vary lift and duration together. That would essentially be giving the engine independent throttle bodies at the valves.

This would still reduce pumping loss because 100% of the air under vacuum is contained within the cylinder and will thus return more energy to the system upon compression. With independent throttle bodies, the throttle is leaking air through all the time vs. only during the intake stroke, so it doesn't have this benefit since the throttle valve must be closed further to reduce pressure to compensate for the "leakage". With the typical plenum and single throttle body setup, you essentially just have a consistent reduced pressure atmosphere after the plenum, and a quick PV diagram lets you see why it doesn't recover as much energy on compression.

The "best" solution is considered to be fully variable duration late intake valve closure since it has the least pumping loss, but it is the most difficult to implement. Early intake valve closure is easy because the systems that reduce lift basically "waste" a portion of the cam lift, all you need for that is an extra rocker that can engage at varying "heights" from the cam's center, but the extra valvetrain mass increases friction, especially at higher engine speed (which is why BMW does not use Valvetronic on the S65 and S85).

Luckily, if we're willing to give up low end torque, cam phasing alone with Atkinson cycle (aka high duration intake cams) can get us pretty low throttling losses. Say you have a 285 degree duration intake cam. If you retard the intake valve opening point to say 10 degrees after TDC (the higher the rod/stroke ratio the better to reduce pumping losses here), the intake valve closes at 295 degrees after BDC. This means you're bleeding off ~60% of the intake charge! Thus to idle you only need to have maybe 50kPa vacuum instead of 80, and when cruising on the highway you only need 20kPa or less vacuum.

Nissan and Toyota do use higher rpm engines though. BMW systems are groundbreaking but they are never simple like the Japanese who later improve upon their ideas.


What do you think about electromagnetic controlled valves (magnetic actuators)? I think it is feasible and could completely eliminate the mechanical linkage (camshaft/springs/etc). The ECU would only then have to control the electric pulses. The only downside I see is what happens if the engine loses electric power then you might run into bent valves as they might not return to their previous position. I guess you could use capacitors to store enough energy to limp the car to a complete stop while still having valve movement.

EDIT: Here is a cool little article that someone combined sources from into one answer: http://wiki.answers.com/Q/Working_of...valve_actuator

Then all we would need is magnetic bearings for the crankshaft and we could almost eliminate the need for oil except for piston lubrication.

Not really. Nissan VQ37s hit 7500rpm but they seem to have very high oil temperature when run at high speed (and their specific torque isn't all that great at the top end) suggesting there is some serious friction going on. No Toyota Valvematic engine runs over 7000rpm.

Camless valve actuation sounds nifty but yes, bent valves when power is lost is a problem.

7500prm is no joke on a 3.7L v6. That is pretty high but I get what you mean. Too-bad toyota doesn't use the valvematic design and make it run like the old vvti-L. Those little celica gt-s pulled pretty good once lift engaged.

Most applications of this design seem to be targeted a slightly smoother torque curve and fuel consumption instead of performance output. Wonder what the long-term liability is like with these cvvl technologies.

Regarding pumping loss, I think it does practically eliminate it, here's why. I hope the logic I have can be followed, cause once I figured it out, I was like, Oh yeah.

1st, keep in mind a deactivated cylinder has no pumping loss, if the valves don't open, the air in the cylinder just acts like a spring and returns whatever energy it took to compress it back on the next downstroke. We can agree on this. If you think otherwise, read this.

2nd, following this idea, if you only let in enough air to operate at 30% power, then opening the valve till the cylinder is half full, then shutting it prior to when it would normally be, you in essence only pull in the air you need, you then essentially draw a vacuum on the cylinder at the bottom half of the intake stroke, and when you compress the half cylinder of air, you have the same result.

The advantage is, you pull in air for only half the stroke when the piston goes from zero to full speed then you quit drawing by closing the valve.....does this make sense, the valve is open when the air velocity is lowest, makes it to where the velocity is about to be at its max, and closes, so there is only a short time that the air is trying to squeeze past a restrictive opening, and this short time is actually very beneficial because it creates a lot of swirling to aid combustion.

Another advantage is the lower cam load, by only working half the time, the cam doesn't need as much power to turn it.

So to paraphrase, the valve at low load is only open at the top part of the stroke when the air velocity is low, so low loss, then for a brief moment there is a high loss/swirl producing intake, then you're back to no pumping loss because the valve is closed, and whatever pressure differential occurs during the bottom half of the stroke will not be a factor.

In my mind I see this as being a way to vary the displacement of the engine without cutting off cylinders.

Hope this didn't further confuse and If I'm missing something I'd sure love to talk more about it cause I'm learning too.

Actually I think the performance is "at its best", because they can utilize a higher maximum lift and duration at the top end with zero low end issues. The Valvematic ZR engines have more power than the non-Valvematic engines.

I think it's useful to think of it as similar to a pushrod valve engine, except the pushrods are lighter and adjustable length. The added mass puts more stress on the cams and requires stiffer springs, and creates more friction. You can rev them up, but the cams can suffer more wear (compared to an OHC engine).