If you read (or skip) past the Corvette "stuff", there is some STS-v info:

http://www.sae.org/automag/globalvehicles/01-2005/1-113-1-8.pdf

- Ray
Who cannot really afford an STS-v, but . . . .

Nice article but, I'm rather surprised they didn't mention anything about the decrease in engine displacement due to a bore reduction. I hate to say "I told you so" but, I think this absolutely confirms what I've always said about the Northstar's head gasket weak spot. Notice Ford didn't have to do any bore reduction when they installed a blower on their 4.6 V8.
I still believe that unless Cadillac ante's up with a new engine, they're destined to be playing second fiddle in the high-zoot road car market. They have a fairly competitive chassis design that NEEDS a better engine.

What it really also needs is direct fuel injection, which will become "standard" on any engine that claims to be high tech in the not so distant future...

Syrob

The interesting thing is that the new transmission is rated at exactly the same torque as the sts-v engine. I guess this means that if anyone wants to make the sts-v go faster (aside from weight reduction), they will have to change out the transmission as well. Did the CTS-Vs in Car and Driver’s supercar challenge keep the existing transmission? (Yes I know, I will never be a road racer, but I like to believe that I COULD be :) )

Of course this could be the classic case of only stating the obvious on pre-release components so the production parts don't miss expectations...

Katshot,

You missed one important point about the supercharged Cobra's engine.

They blew up so many aluminum 4.6Ls that they had to do it in IRON!!!

I would say the weight penalty is much worse than the bore reduction.

Katshot,

You missed one important point about the supercharged Cobra's engine.

They blew up so many aluminum 4.6Ls that they had to do it in IRON!!!

I would say the weight penalty is much worse than the bore reduction.

:yeah:

Regarding the bore decrease, it should also be noted the the supercharged Northstar, is a Closed Deck design. This gives a greater sealing area for the headgasket.

It will be interesting to see how well it holds up in daily driving and "spirited" runs.

I sure do like the looks of this new version.

-George

There are actually quite a few things different about the SC Northstar block. It is a sand casting that is heat treated....the production engines have always been diecast blocks. The deck is closed on the SC engine while the NA engines have always had an open deck. The SC engine block has features for the oil gallery for the dedicated piston oil squirters where the NA engines have none. The coolant passages in the sand cast SC block are larger and shaped for improved flow to improve the coolant circulation rate for the increased output. In addition, the sand casting process allows the windage "windows" in the block to be smoothed and radiused for better windage flow thus adding to the power level by reducing windage loss. The block is really a dedicated piece for the SC engine and has other design features and bosses and such dedicated just to the SC design. That is why it was made a sand casting and taken out of the normal production and machining stream for the NA Northstars.

Katshot....do you EVER have anything good to say about GM or Cadillac or the Northstar engine....????......if we said that the Northstar could now cure cancer you would complain because we left out malaria or something.....

Just because an engine design feature was changed to account for increased output does NOT mean that the existing design is weak or substandard. The SC engine makes a LOT more power than the NA version and has much greater cylinder pressures which account for the reason for the redesign in certain areas. If we could have plugged a supercharger on the existing engine with no changes there would probably be people like Katshot on here complaining that the engine was obviously OVERDESIGNED all along......get a life.


Realize that the SC engine is actaully making well over 500 HP....but the parasitic load of the blower eats up considerable power to turn the supercharger. The net power output is 440 but the actual power into the crankshaft is well over 500....so....the engine had to be designed for almost 200 HP MORE than the NA version....

What it really also needs is direct fuel injection, which will become "standard" on any engine that claims to be high tech in the not so distant future...

Syrob


For my own interest.....could you explain what exactly is the advantage of direct injection and why would any engine that claims to be "high tech" in the future need direct injection...???? I am curious as I see little or no real advantage to direct injection....other than increased cost and complexity....LOL.

For starters....direct injection is great for allowing a gasoline, spark ignited engine to operate very lean...but....lean doesn't work with the existing catalysts, they have to be at stochiometric (14.7:1) to clean up the exhaust. Since no gasoline engine is even remotely close to meeting emission standards without a catalyst it makes the issue of direct injection somewhat moot. So, what other advantages are there to all the extra cost and complexity or is it just an aura of "high" tech surrounding it...???

Direct Injection advantages? -- that's a great question. I know some of the answers, but not all. The claims are improved power and reduced fuel consumption.

With direct injection, fuel is sprayed directly into the cylinder, typically with an injector close to and/or aimed at the spark plug. With indirect injection, fuel is sprayed into the intake port and is aimed at the intake valve.

Direct Injection advantages:

At low loads, fuel can be injected close to the spark plug, and very close to ignition time so that you can approximate stratified charge - a small volume of combustable mixture near the plug, but a lean mixture overall, relative to the volume trapped in the cylinder. This provides more reliable combustion of a stoichiometric (or nearly so) kernal of air/fuel mix near the plug. In a port-injected or carbureted engine, more fuel must be squirted in to allow reliable combustion of after homogeneously mixing with a sparse amount of air and some trapped exhaust while operating with small throttle opening conditions.

Under warm up conditions, there is no fuel in the intake runners or sprayed on a carboned-up intake valve so less fuel condensation and/or absorption. This allows smoother warm-up performance with less fuel injected.

With variable valve timing, the EGR valve may be eliminated as greater valve overlap can provide more trapped exhaust gas to reduce combustion temps and thereby NOX. With direct injection, the fuel is not injected until after the intake valve is closed (for low-med loads) so it can't escape out the exhaust valve (lower HC and improved fuel economy) during overlap.

For improved power, the fuel is injected directly into the cylinder where its vaporization results in more cooling of the trapped air volume, as opposed to squirting it indirect, onto a hot intake valve and hot port walls, where much of the cooling effect is lost.

Katshot....do you EVER have anything good to say about GM or Cadillac or the Northstar engine....????......if we said that the Northstar could now cure cancer you would complain because we left out malaria or something.....
bbob, you said a mouthfull, if only Ford hadn't surrendered this market and given up, He'd have some hope!:deadhorse

Direct injection?



Get a diesel :D

Direct Injection advantages? -- that's a great question. I know some of the answers, but not all. The claims are improved power and reduced fuel consumption.

With direct injection, fuel is sprayed directly into the cylinder, typically with an injector close to and/or aimed at the spark plug. With indirect injection, fuel is sprayed into the intake port and is aimed at the intake valve.

Direct Injection advantages:

At low loads, fuel can be injected close to the spark plug, and very close to ignition time so that you can approximate stratified charge - a small volume of combustable mixture near the plug, but a lean mixture overall, relative to the volume trapped in the cylinder. This provides more reliable combustion of a stoichiometric (or nearly so) kernal of air/fuel mix near the plug. In a port-injected or carbureted engine, more fuel must be squirted in to allow reliable combustion of after homogeneously mixing with a sparse amount of air and some trapped exhaust while operating with small throttle opening conditions.

Under warm up conditions, there is no fuel in the intake runners or sprayed on a carboned-up intake valve so less fuel condensation and/or absorption. This allows smoother warm-up performance with less fuel injected.

With variable valve timing, the EGR valve may be eliminated as greater valve overlap can provide more trapped exhaust gas to reduce combustion temps and thereby NOX. With direct injection, the fuel is not injected until after the intake valve is closed (for low-med loads) so it can't escape out the exhaust valve (lower HC and improved fuel economy) during overlap.

For improved power, the fuel is injected directly into the cylinder where its vaporization results in more cooling of the trapped air volume, as opposed to squirting it indirect, onto a hot intake valve and hot port walls, where much of the cooling effect is lost.


I agree with your synopsis but consider the following...

While the stratified charge approach will allow lean operation with DI the engine cannot be operated lean of stochiometric because the catalyst will not function....so....moot point. It would be an advantage if the cat could work lean but it won't so it isn't. Both port fuel injected engines and DI engines must run at 14.7:1 or stochiometric so make the 3 way cats work.

You do not need DI for eliminating the EGR valve and accomplishing internal recirc via retarded exhaust valve timing. The inline six cylinder Vortec engines in Trailblazers and such do that exact thing...no EGR valve and VVT on the exhaust cam. The rear wheel drive Northstars in the XLR/SRX/STS do not have an EGR valve either....VVT accomplishes the internal recirc. So does the upcoming SC Northstar...VVT eliminates the need for an EGR valve. So....DI ???...not an advantage here, either.

Possible warmup advantage....but...with high pressure port fuel injection the engine is stochiometric and closed loop in 45 to 60 seconds anyway on a cold start so there is precious little advantage here, either. Besides, most engines today that meet LEV and SLEV emissions start the engine on the cold start overly rich with retarded spark timing to light the catalyst by sending the still-burning fuel down the exhaust pipe to the cat. You would need to do this with DI so there is now no advantage with DI here.

You did hit on the one small advantage in terms of performance...the cooling effect of the fuel spraying directly into the chamber can improve power slightly....but....for the cost of DI it is a very poor tradeoff and for the same money much more performance can be gained in other ways. So....DI is a questionable approach purely for performance.

You forgot to mention running the engine lean for fuel economy... Audi capitalized on this approach with their LeMans prototypes which were DI...but, once again, you cannot run a passenger car lean because the cat will not work. So, what can be used on a race engine will not work on a passenger car with DI.

See my point...?? DI is often touted as a fantastic technical miracle...when, in reality, it offers very little real advantage. Most of the allure is the perceived "technology".....whether it really does anything or not.

I agree, DI is not a miracle.

But DI is becoming a part of the automobile The Japanese have implemented it in small engines and BMW has brought it to market in a number of its larger engines. BMW talks about 12% improvement in both fuel economy and peak power.

You are correct about the 3-way catalyst problem. These work at stoichiometric ratio, which is far too rich for optimum fuel economy during most driving conditions. The Japanese are using 3-way catalyst plus lean catalyst for small engines with DI.

You are also correct that it isn't so much DI that allows elimination of the EGR valve; it's high-overlap valve timing that traps exhaust gas in the cylinder under low loads to reduce NOX emissions. The normal side effect of high-overlap timing is unburned fuel escaping past the exhaust valve and also unburned fuel pumped back into the intake system. We'd really prefer the injected fuel to remain trapped inside the combustion chamber and preferably near the spark plug where it can be ignited readily. We can crutch around these side effects with higher compression ratio four-valve engines that allow higher peak torques for respectable max performance and computer controled idle air controls to allow reasonably smooth idling and off-idle performance.

Throttling losses cripple efficiency at low loads in the spark ignition engine. Diesel engines realize superior efficiency at low to medium loads because the diesel engine does not have to wheeze air past the restriction of a nearly closed throttle valve under cruise conditions. The combination of variable valve timing and DI provides potential for substantially reducing throttling losses.

The dream of stratified charge is only recently closer to reality with DI and advanced fluid flow modeling capabilities. Stratified charge is a many-decades-old dream that promises improved fuel economy at low (cruising) loads. The goal, again, is to control the fuel so that it resides in a relatively rich, easy-to-ignite kernal around the spark plug, at the time of igntition. Surrounding air and exhaust will then serve to buffer maximum temperatures to inhibit NOX formation. With reduced NOX formation, the 3-way catalyst and its gas-hog stoichiometric requirment is no longer so necessary.

The main benefit offered by DI is control -- much more precise control of not only the amount, but even more importantly, the timing of fuel delivery in the combustion cycle. DI will prove an important tool, just as the affordable engine control computer was, to continually improving the seemingly opposing goals of increased power and driveablility, reduced emissions, and reduced fuel consumption.

...
With direct injection, fuel is sprayed directly into the cylinder, typically with an injector close to and/or aimed at the spark plug. With indirect injection, fuel is sprayed into the intake port and is aimed at the intake valve.

Direct Injection advantages:

At low loads, fuel can be injected close to the spark plug, and very close to ignition time so that you can approximate stratified charge -
...


My own experience is limited to diesel injection and have no first hand knowledge of gasoline systems. I was wondering why you mention that the injector was directed at the spark plug rather the the practice of directing at the exhaust valve as in diesel design. The advantage is to cool the exhaust valve and better vaporizing of available fuel. I have seen diesel injected at glow plugs but mostly for starting systems.

The advantages as I understand them are that of superior atomizing for under high pressure you will get a significantly finer mist hence better vaporization. Unlike low pressure port injection where there are still some droplets at the time of ignition which will eventually burn but not cleanly, the finer mist is converted to vapor with nominal droplets if they exist at all. Certainly if you have no droplets then you wouldn't run the risk of fuel fouling the plugs which still occurs with port injection.

Cheers,
GTM2u

Good questions.

Diesels (for truck and construction use) are designed for continuous duty at heavy loads. As you say, aiming the diesel injector at the exhaust valve makes sense because it cools the exhaust valve. Also in a diesel, we want the fuel to ignite asap upon injection so aiming it at the hottest spot in the cylinder speeds auto ignition.

Automotive engines are optimized for low load (cruising) operation and occasional full power duty.

In automotive DI, aiming fuel close to the spark plug allows small amounts of fuel to ignite near the spark for smooth, low emission operation at low loads.

You are right, the high pressures required by DI allow fine atomization, but the port injection engine otherwise has time and heat on its side. In other words, by injecting fuel into the port, the heated intake valve and intake port walls heat the more poorly atomized port-injected fuel. Port injection also provides more time for vaporization compared to DI (fuel is injected during the intake stroke for port injection as opposed to DI, in very low loads, which occurs much later, after the compression stroke). Finally with port injection, fuel is injected into a 'vacuum' which greatly improves vaporization.

In other words, DI has a lot going against it in terms of fuel vaporization, so the DI atomization better be damned good!

You guys missed a few key points. Number one you are right the lean burn advantage of DI can not be used due to the ability of the catalyst to handle it and our gas. In Europe they can use the function. The main benefit of DI allows them to run higher compression ratios than would normally work. For instance the Audi FSI motor runs 12.5 to 1 compression. And it also is great for turbo engines because it allows higher compression to be run on them as well. At full load, the fuel in injected synchronously with the air intake phase. This fills the combustion chamber homogeneously. Here again, this produces a definite reduction in fuel consumption together with higher power-output and torque figures than would be possible indirect fuel injection. This was demonstrated on the race-winning Le Mans engine, which runs permanently in the homogeneous mixture mode. This has the advantages of reducing the tendency to knock as a result of direct fuel injection into the combustion chamber and the resulting internal cooling effect. In addition, the engine is capable of operating at a higher compression ratio.

Their is another issue that has been somewhat skirted in this discussion of direct injection that is very important.

Since the fuel is injected into the chamber there is a very small "window" of time or crank angle in which all the fuel must be injected. Basically, the window of allowable injection is from after BDC (when the exhaust valve is finally closed) to the point of ignition (30 degress at the latest before TDC in round numbers) So....all the fuel must be injected into the chamber within 130 degrees of crank angle. 180 degrees would be the absolute most and allowing 20 degrees ABDC for the exhaust valve to close and 30 degrees for the spark advance you get 180 - 20 - 30 = 130. This is a VERY small window of crank angle when the engine is at high RPM to be able to inject the fuel. You need a very high capacity injection system to handle this.

Port fuel injection, however, injects the fuel into the port on the back of the closed inlet valve so there is ample crank angle/time to get all the fuel in. Compared to the 130 crank angle allowed for DI, the same port fuel injected engine has about 490 degrees of crank angle rotation to get the fuel in....that would come from the 360 degrees of compression and power and the 130 degrees of rotation for the exhaust event.

The much longer allowable time for the port fuel injection system allows a much more reasonable fuel injection system capacity and injector size.

DI does NOT start until the exhaust valve is closed completely or part of the fuel being injected would just go out the exhaust. As long as the exhaus is open the DI fuel is being injected directly beside the exhaust valve so it has to be closed completely.

The reason that this is important is that , especially on a racing engine, this limits the amount of fuel that can be injected by DI due to the short time interval allowed for DI injection...especially when racing engines start to rev above 10,000 RPM. Audi was successful at LeMans with DI strictly because of the rules at LeMans. The class rules require pretty severe inlet restrictor orifices. With the inlet orifices (think "restrictor plates" as in NASCAR) reducing power considerably and totally limiting air flow at higher RPMs an engine designed specifically for LeMans is designed to operate at relatively low RPM....probably not much over 9000 RPM. Plus, since at 9000 the restrictors are restricting flow heavily and creating inlet manifold vacuum, the charge density in the chamber is getting lower and lower (which is why it limits the power) so leaner operating conditions can be tolerated. Good thing, as the DI can scarcely get enough fuel in at those RPMs due to the narrow time/crank angle window. Bottom line....DI is not all it is cracked up to be...and you are not likely to see DI on other racing engines as it specifically fits the LeMans requirements due to the odd rules. Also, note that Audi, in their technical references, never claimed any power gains with DI...just that it allowed leaner operation under certain conditions (where the charge could be deliberately stratified to maintain combustion with the lean mixture) thus allowing better fuel economy. This added up to two less pitstops for them during the race which accounted for most of their time advantage. The cost of developing a DI engine specifically for LeMans for only one race per year has kept other manufacturers from doing the same.

It is true that DI adds some cooling effect to the chamber allowing more compression ratio....but....most of this is lost if you are running the engine lean for fuel economy. Audi used it to exploit the rules at LeMans but it is not very usefull elsewhere.

All the rhetoric about DI sounds good and sounds high tech but it is really not that advantageous at all in the real world.

The Audi R8 never ran in lean burn mode...it always ran in homogenous mode.
And you are correct they don't even like to rev the motor much past 7000 rpm because of the intake restrictions. The fuel savings were not acheived by using lean burn. Homogenous operation eliminates the inefficiencies of
port fuel injection. The air fuel mix is pretty much uniform thru out the combustion chamber. Increased efficiency improves power/ torque and mileage. The cooling effect of the fuel combats against the detonation you would normally experience running that high of compression ratio. But lets not forget the R8 was designed to be taking apart very easily with problems. Tranny goes bad? Great they pull the whole back half of the car off and 30 minutes later their done. That is the main reason they are unbeatable aside from DI.

And also even if the only advantage was he ability to run 12.5 or 13 to 1 compression ratios than you would have power and torque increases. So it would be a valid technology..but their is so much more.

The interesting thing is that the new transmission is rated at exactly the same torque as the sts-v engine. I guess this means that if anyone wants to make the sts-v go faster (aside from weight reduction), they will have to change out the transmission as well. Did the CTS-Vs in Car and Driver’s supercar challenge keep the existing transmission? (Yes I know, I will never be a road racer, but I like to believe that I COULD be :) )

Of course this could be the classic case of only stating the obvious on pre-release components so the production parts don't miss expectations...

This is the case for basically all GM tranmissions. The tranny in the STS V8 is a beefed up version of the V6 tranny... Guess what? They beefed it up JUST enough to handle the power of the V8.

http://www.seriouswheels.com/top-2005-Cadillac-STS-SAE-100.htm

http://www.seriouswheels.com/top-2005-Cadillac-STS-SAE-100.htm

Great pics Ralph!!!

You got the best pics anyhow!!!:thumbsup:

Do you have one from the XLR V in black-raven???????

Thanks
Harry

Do you have one from the XLR V in black-raven???????


I'll keep my eyes open Harry. ;)

Didn't that sae paper rate the sts-v tranny torque holding at 900NM and the sts-v's engine output at 583NM? Doesn't sound like its at its max capacity..

One thing that needs to be clarified (others in this thread have only implied it) is that DI allows the elimination of a throttle altogether. Since the throttle makes up the majority of the pumping losses, a significant increase in fuel economy is noted.

The best economy is attained when the throttle is wide open (or in this case, eliminated) at the peak torque RPM of the engine. This is one reason why diesels get such good efficiency - they normally have no throttles and their peak RPMs often very low. Many diesel engines' peak RPMs are around 1800 RPM.

This discussion has missed the big thermodynamic advantage of direct injection: DI allows the potential for a staged charge injection with fuel addition continuing as the flame front advances. This allow the burn to get closer to the ideal of an isobaric expansion which is much more energy efficient than a turbulent, explosive flame front slamming against the piston as you get with a single charge.

Staged charge injection is relatively easy to achieve in a diesel because the flame front velocity is much lower. Gasoline burns at a much higher flame front velocity which will make it much harder to time a multi-stage injection to capture the potential benefits. Audi seems to be making some progress but most of what you see in their hp numbers is simply the effect of going to much higer rev limits, i.e. nothing spectacular yet on the torque side.

One thing that needs to be clarified (others in this thread have only implied it) is that DI allows the elimination of a throttle altogether. Since the throttle makes up the majority of the pumping losses, a significant increase in fuel economy is noted.

The best economy is attained when the throttle is wide open (or in this case, eliminated) at the peak torque RPM of the engine. This is one reason why diesels get such good efficiency - they normally have no throttles and their peak RPMs often very low. Many diesel engines' peak RPMs are around 1800 RPM.


This "clearification" is seriously in error....LOL.

A DI gasoline engine still has a throttle blade. DI gasoline engines simply inject the fuel directly into the combustion chamber. The fuel burn is still initiated by the spark plug and the engine is still throttled by a throttle blade.

In a diesel the fuel starts to burn as it is injected since it achieves the heat of combustion from the compression. Only enough fuel is injected to create the work required. Most of the time the diesel is operating well lean of stochiometric. The diesel will still run on very lean mixtures like this because the fuel is igniting from the heat in the chamber (not relying on a spark to initiate combustion in a combustable mixture) and it always has surplus air to oxidize with.

The gasoline direct injection system does NOT work like this and still uses the spark plug to initiate combustion and still throttles the engine with a throttle blade. Since the burn is inititated by the spark plug the mixture must still be near stochiometric so as to be combustable. A DI engine can run leaner than a conventional homogeneous charge gasoline engine since the fuel can be injected near the spark plug to create a rich "cloud" in the area of the plug that is combustable. But it can never operate at the ultimate lean levels of a diesel if it relies on the spark ignition so it must still have a throttle blade to control the engine.

That is why the diesel injects fuel in the neighborhood of the exhaust in some cases....it is injected into the hottest part of the chamber for good combustion....not to cool the exhaust valve. The DI gasoline engine injects near the spark plug so as to have the cloud of rich (combustable) mixture near the spark so as to be sure of initiating combustion.

It is true that a diesel gets much of it's efficiency from operating unthrottled. But it is not true to say that a DI gasoline engine operates the same way. It doesn't.

This discussion has missed the big thermodynamic advantage of direct injection: DI allows the potential for a staged charge injection with fuel addition continuing as the flame front advances. This allow the burn to get closer to the ideal of an isobaric expansion which is much more energy efficient than a turbulent, explosive flame front slamming against the piston as you get with a single charge.

Staged charge injection is relatively easy to achieve in a diesel because the flame front velocity is much lower. Gasoline burns at a much higher flame front velocity which will make it much harder to time a multi-stage injection to capture the potential benefits. Audi seems to be making some progress but most of what you see in their hp numbers is simply the effect of going to much higer rev limits, i.e. nothing spectacular yet on the torque side.



Hmmm....not so sure of this either.

No question that a stage charge is used with the current common rail diesels with electronic controls. Huge improvement in diesel combustion with this not question.

A staged charge with gasoline direct injection is questionable. Since enough fuel must be injected to achieve a combustable (not very lean) mixture at the plug and the chamber MUST have good turbulence and in cylinder mixture motion to achieve a reasonably homogeneous mixture during the burn injecting fuel later in the ignition cycle, after the spark plug has already initiated the burn is unlikely to be very effective. The mixture in the area of the injection/plug will have already burned and there will be nothing but an inert cloud of already/combusted material there and there will be no oxygen left for the additional fuel to burn with. I just don't see a gain from trying to stage the injection with the DI engine like with a diesel due to the spark ignition requirement.

Possibly this would work with a second or third spark event??? Any reference to anything like this being done in the industry??

In any case, the DI gasoline engine is a completely different animal from a combustion standpoint when compared to a diesel. Apples and oranges. Just because both inject the fuel directly into the chamber does NOT mean they share combustion characteristics.

if I remember from my reading of DI engines, they are now more common because in conditions where regular injection is need the engine does that, but in situations where DI is best that is used, computers havea heck of a way of solving problems of the past (like the 80's cadillacs with cylinder deactivation, now we have them w/o any problems because of how computers have advanced).

if I remember from my reading of DI engines, they are now more common because in conditions where regular injection is need the engine does that, but in situations where DI is best that is used, computers havea heck of a way of solving problems of the past (like the 80's cadillacs with cylinder deactivation, now we have them w/o any problems because of how computers have advanced).


I think there is some confusion in the discussion. An engine cannot switch between DI and normal injection.

DI engines are Direct Injection engines....i.e...the fuel is injected directly into the combustion chamber rather than into the intake port a la "conventional" port fuel injection. This requires a fundamental difference in injection hardware....not something that the computer can switch back and forth between. Direct injection engines must have provisions for the fuel injectors machined directly into the combustion chambers (just like a spark plug), special injectors are needed and the fuel system must run at several thousand PSI to overcome combustion pressure in the chamber. Conventional port fuel injection operates at a relatively "low" 50 PSI (approx) and the injectors are simply located in bungs in the intake manifold or the intake port, not inside the combustion chamber.

No question that computer control allows a much much higher level of sophistication in the control of the hardware than in the past. The control of the DOD system allows seamless switching between cylinder cut out and normal operation where the cylinder cutout on the '81 Modulated Displacement system on the Cadillacs did leave a telltale bump or "feel" as it switched cylinders.

yep your right, my memory recalled wrong. This is what I ment:

"Injection

Article by : Duane Bong

In traditional gasoline engines, fuel is injected into a port before it enters the combustion chamber. The use of a port gives the fuel time to evapourate and mix uniformly with the air that it will be burnt with. However, this is not ideal because it provides little control over the air and fuel mixture.

Gasoline Direct Injection engines do not inject fuel into a port. These engines inject the fuel directly into the combustion chamber instead. This approach gives control over the air/fuel mixture and allows the engine to operate in 2 modes:

Stratified Mode

Stratified mode is used when the engine is operating at low and medium loads. Fuel is injected into the chamber just before a spark ignites it. This allows very little time for the fuel to mix with air in the combustion chamber. As a result, the composition of the air and fuel mixture varies within the chamber. It is rich near the spark plug and lean in regions further away from it. A rich mixture is required near the spark plug to aid ignition. However, the overall composition of the mixture is lean and this reduces fuel consumption.

Homogeneous Mode

When a GDI engine needs to run at higher loads, it switches to a homogeneous mode to provide more power. For such situations, fuel is injected into the engine early during the induction stroke. This provides sufficient time for the fuel to mix uniformly with the air in the chamber and form a rich homogenous mixture for maximum power."

This "clearification" is seriously in error....LOL.

A DI gasoline engine still has a throttle blade. DI gasoline engines simply inject the fuel directly into the combustion chamber. The fuel burn is still initiated by the spark plug and the engine is still throttled by a throttle blade.

LOL. BMW ships a 12-cylinder DI Valvetronic engine that has no throttles. However, GM's new DI engines have throttles.

The BMW Valvetronic-equipped 4-cylinder engines that are currently shipping also have no butterfly throttles, either. However, the 4-cylinder is not DI, it's port injected. So, it is interesting that DI isn't necessary for throttleless operation in a gasoline engine. Did you know this? I certainly didn't.

I'm not aware of all the engineering challenges that results in getting rid of the throttle(s) in a DI engine, such as an excessively lean mixture, but the engine guys are certainly working this out.

I was talking recently at length to an Audi Powerplant Engineer who was visiting a friend here in the states. He was in Denver to give a lecture on something related to engine design (darn, I should have grabbed a copy of his paper). Anyways, during our discussion, he said the new DI Audi gasoline engines will have not have throttles. I don't know when they will hit the market or if they have already. Very interesting.

One problem immediately popped into my head and that was high NOx that might result. Unfortunately, he didn't get around to answer my question completely. The solution is new catalytic technology. But the problem of high sulfur content in US fuels is going to kill the new converters.

Back to the BMW Valvetronic, the gas pedal instructs the computer to vary the amount and duration of valve lift. I would love to see the CPU algorithms and control equations that govern this.

Anyways, back to your last point, that DI gasoline engines don't operate the same as DI diesels. I didn't say that they did. My point was that getting rid of the throttle will eliminate the biggest source of pumping losses. My mistake was implying that DI is necessary for the elimination of a throttle in a gasoline engine. BMW proved me wrong even before I wrote that.

By the way, this is probably the BEST thread on this board that I have seen in a LOOOOONG time.

Yes, DI and Valvetronic are totally separate and independent technologies. They obviously do not require each other to be employed. And....it would be more correct to say the valvetronic engines do not have a throttle blade as they are still throttled...only by the intake valve instead of the throttle blade. BTW...I've seen "valvetronic" type systems that varied the intake valve lift to act as the "throttle" 30 years ago in research situations running with carburetors...LOL.

The reason I made the point that DI gasoline engines are different from diesels (that do not use throttles) is that diesels truely run unthrottled from a pumping standpoint. They are completely controlled by the amount of fuel injected. DI engines are still spark ignited gasoline engines therefore there must be a combustable mixture in the combustion chamber so they cannot operate lean enough to control idle speed completely with fuel....like a diesel does. It seemed like there was confusion between the technology of DI and throttleless operation. As the point was being made that DI engines operated throttleless that would imply that they operated like diesels...which they don't.

The idea of valvetronic is just a different way of throttling the spark ignited gasoline engine. A throttle blade in a conventional throttle restricts the air flow at a point prior to the intake manifold or the intake port (in the case of individual throttle blades at each inlet port). The valvetronic system does much the same by severely limiting valve lift. That just moves the restriction from the throttle blade to the intake valve. The amount of mixture injested by the cylinder is still throttled and controlled so it is not truely "unthrottled" operation like a diesel so the engine does not realize a significant reduction in pumping losses.

Pumping losses come from the fact that the throttle blade creates a restriction in the intake flow. This results in vacuum in the intake manifold. When the piston is moving down on the intake stroke the vacuum acting on the piston when the intake valve opens further impedes the motion of the piston causing greater work to be expended to continue it's downward travel. If the piston didn't have to work against vacuum (like a diesel) it would reduce the pumping losses. The intake valve only opening a tiny amount in the valvetronic system creates the same restriction so the piston is still moving downward against vacuum and thus incurs the same pumping loss. It is just harder to measure the "vacuum" as there is no vaccuum in the intake manifold but it is effectively there just after the intake valve since the intake valve is now the throttle.

One way of measuring this and proving it is to run the engine with in-cylinder pressure transducers and monitor and compare in-cylinder pressure between and engine running with a throttle blade and an engine with some sort of "valvetronic" system. You will see the same in-cylinder pressure (or lack thereof) during the intake stroke for either system.

Sooo... Valvetronic offers some advantages for idle speed and load control at idle but it really doesn't reduce the pumping losses any from a conventional throttle setup. Unlike a diesel, the valvetronic engine is still throttled, just in a different way. Another advantage of valvetonic is that at light load conditions when there is low air flow thru the engine there is significant velocity and turbulence created by the very small valve opening so that can help with fuel atomization and in-cylinder mixture motion which can help combustion characteristics under light load where emissions and fuel economy are in the forefront. Additionally, valvetronic, by constantly changing the valve lift, in effect, reduces the cam lobe duration at idle and low speeds where the valve is not opening fully. This also promotes good combustion and less cylinder pressure bleeddown and reversion. In other words, the engine can run a very radical cam profile and the valvetronic will reduce it's effect at idle and low speeds thus taming it down. Not knocking valvetronic but it's advantages are minor in comparison to the extreme cost and complexity of the system. Possibly why it hasn't caught in a wide variety of applications.


DI allows non-homogeneous mixture control in the combustion chamber and allows very lean overall operation of a spark ignited gasoline engine. Unfortunately, since there is yet to be a catalytic converter invented (for commercial use) that can reduce NOx under lean conditions this feature of DI cannot be used in passenger cars that must meet emission requirements.

DI also cools the combustion chamber significantly compared to other forms of introducing fuel into the spark ignited gasoline engine so this becomes an "enabler" for higher compression ratios (improved thermal and mechanical efficiency) and/or higher boost levels in super/turbocharged applications. This is the main driver for using DI on passenger cars from what I can see. Otherwise, it really isn't that effective.

But, both DI and Valvetronic have very "high tech" images in the market place so they are also employed for that reason....

Just wanted to say Im enjoying reading this duscussion!

Hi Chevelle,

Precisely! Where the engine needs to be throttled, they do it by altering lift and duration. This much is widely known.

What their system potentially allows for is much reduced pumping losses when the valve is fully open. How much they do in practice is another question. I'm sure emissions regulations play a huge part in the valves' profile. I don't think anyone except BMW knows what the lift and duration profiles are with their Valvetronic system. Unless, perhaps, you're privy to this information?

In any case, imagine the efficiencies gained if the system allowed the intake valves to open fully. This might indeed be happening at low-power settings where the pumping losses are greatest in a butterfly throttle-equipped system. I'd say it's safe to assume that this is exactly what is happening during high-power operation. I would also suspect that high-lift and duration modes are employed frequently in various power settings. If this indeed does happen, there's much less or no throttling action in these modes because of the lack of a throttle plate. I wonder if BMW has a paper on this someplace.

You mentioned that the valves in the Valvetronic system open just a tiny amount. I assume that you have found this fact in print somewhere. I would love to read it. Care to share it?

You also mention that the "in-cylinder pressure (or lack thereof) during the intake stroke [is the same] for either system". I assume you also have research papers from BMW or other noteworthy organization regarding this? If so, please share it with us, I think many of us would dearly LOVE to read it.

What such a system allows, as complex as it is, is for a drastic reduction in pumping losses. I don't know if we'll ever see the total elimination of throttle-type pumping losses (a-la diesel), but I think the boys at BMW have eliminated a big chunk of it with this Valvetronic system. You can bet its elimination is also high on the list of targets of engine designers across the industry now that some of the technology has arrived that allows them to do this. It looks like gasoline engines are slowly approaching the diesel ideal in terms of pumping losses. I think they're still a long way off, but it looks like my fellow Engineers are making good progress.

Not to say you're pulling these facts out of your butt, but I just haven't seen literature *anywhere* supporting it. I think BMW is keeping tight lipped about it either for competitive reasons (don't want their methods copied) or because Valvetronic is just a big waste of money (because, as you say, they have accomplished zero in regards to pumping losses).

One thing is certain, though, Valvetronic is a very complicated and VERY expensive system. Road and Track Magazine lists the VANOS system (Valvetronics' predecessor) as the number one thing to watch out for when buying a used BMW. If VANOS fails, expect a five-figure repair! I can't imagine what it will cost should the Valvetronic system fails. Holy Smokes.

An interesting thought just occured to me whilst writing this. We see all this activity amongst the car manufacturers in the gasoline DI arena. Too bad diesels are not allowed to prosper in the US. I understand that diesels make up 40% to 50% of new car sales in Europe (I pretty much pulled those figures out of my butt, but I think they're close). Diesel DI technology is very mature; too bad our politicians have "throttled" it!

However, the car manufacturers are not standing still on this. The fella from Audi I mentioned earlier in this thread says they're making great strides in cleaning up diesel particulate emissions. Their greatest challenge? It's dealing with the EPA. To make a long story short, he says the EPA keeps changing the way they rules are interpreted. In other words, the EPA makes life hard for the foreign diesel makers. I guess there's no place where politics doesn't screw things up. This is especially sad since the Europeans have the best diesel technology in the world and have much more experience at it.

[quote=thu;836329]Hi Chevelle,

Precisely! Where the engine needs to be throttled, they do it by altering lift and duration. This much is widely known.

What their system potentially allows for is much reduced pumping losses when the valve is fully open. How much they do in practice is another question. I'm sure emissions regulations play a huge part in the valves' profile. I don't think anyone except BMW knows what the lift and duration profiles are with their Valvetronic system. Unless, perhaps, you're privy to this information?

In any case, imagine the efficiencies gained if the system allowed the intake valves to open fully. This might indeed be happening at low-power settings where the pumping losses are greatest in a butterfly throttle-equipped system. I'd say it's safe to assume that this is exactly what is happening during high-power operation. I would also suspect that high-lift and duration modes are employed frequently in various power settings. If this indeed does happen, there's much less or no throttling action in these modes because of the lack of a throttle plate. I wonder if BMW has a paper on this someplace.

You mentioned that the valves in the Valvetronic system open just a tiny amount. I assume that you have found this fact in print somewhere. I would love to read it. Care to share it?

You also mention that the "in-cylinder pressure (or lack thereof) during the intake stroke [is the same] for either system". I assume you also have research papers from BMW or other noteworthy organization regarding this? If so, please share it with us, I think many of us would dearly LOVE to read it.

What such a system allows, as complex as it is, is for a drastic reduction in pumping losses. I don't know if we'll ever see the total elimination of throttle-type pumping losses (a-la diesel), but I think the boys at BMW have eliminated a big chunk of it with this Valvetronic system.

Not to say you're pulling these facts out of your butt, but I just haven't seen literature *anywhere* supporting it.


Their greatest challenge? It's dealing with the EPA. To make a long story short, he says the EPA keeps changing the way they rules are interpreted. In other words, the EPA makes life hard for the foreign diesel makers. quote]




I still sense a misunderstanding of what the valvetronic system does and what it can do.

Valvetronic basically alters the total valve lift to the point that at low loads the valve lift is very slight and thus the valve itself becomes the throttle. This does not reduce pumping losses. It just moves the throttle point to another spot in the system and the pumping losses are the same. The system does not alter "duration" per se. The valve lift profile of the cam is always the same....it is just reduced by a percentage at each point. This ends up changing the "effective duration" as the valve lift at low lifts is dramatically reduced to the point that very little to no flow occurs but the actual valve lift profile of the cam does not change.

The only system that actually changes the actual cam life profile completely is the Honda VTEC (that shifts the lift profile to a different cam lobe via a rocker arm lockup arrangement) and the Porshe system that uses a two different diameter lifters to engage two different cam profiles. The other systems on the market change cam centerlines or cam timing (some on the intake, some on the exhaust and some on both). The VANOs changes the cam timing on BMW engines and the Valvetronic sytem adjusts the total cam lift to effect the throttling.

If the valve is "fully open" how would the Valvetronis affect pumping loss?? It doesn't. Once the system adjusts the total lift to 100% of the design intent of the cam profile the pumping loss is the same as any other cam with that lift and duration spec. No difference in pumping losses due to Valvetronic. Besides, as previously mentioned, Valvetronic does not affect the pumping loss anyway....once again, it just moves the throttling point from the throttle blade to the valve itself.

Privy to this information...??? Go to any major auto show and look at the BMW cut away engines and see the hardware for yourself. There are numerious technical articles in the trade magazines about VANOs and Valvetronic and the other systems that make it abundantly clear how they work. The marketing guys are taking liberties with what Valvetronic can and cannot do. Fact is that a spark ignited gasoline engine has to be throttled some way....Valvetronic just does it by restricting the air flow at the valve interface by limiting lift, thus the pumping losses are the same. Just because you have not done any research or reading on this system does not mean that there is no information out there. For starters, look at SAE papers. BMW loves to publish SAE papers and their engines are frequently covered in detail in the mouth piece of the SAE, the AUTOMOTIVE ENGINEERING magazine. It is a "free" publication to those in the industry. Other magazines such as WARD'S AUTOWORLD also cover the specifics of these types of technologies.

As far as imagining what the " efficiencies gained if the system allowed the intake valves to open fully"......that is what happens when the Valvetronic is allowing the cam life to open 100% of it's capability. The engine makes the advertised HP. That is all that happens. Nothing magic or else to expect. The cam lobe profile and valve lift event is driven by the cam dynamics and valve spring capability. Valves still have to be controlled with V'tronic just like as with any other system. So V'tronic has no advantage here. It just allows a given cam life profile to be reduced to effect throttling so as to eliminate the throttle blades. I indicated the advantages of V'tronic in my previous post. Certainly it allows a rather radical cam life profile to be reduced for lower speed and idle control of airflow but it doesn't do anything magic once the system is restored to full lift compared to what it would do without Valvetronic. So there is really nothing to imagine here. Just drive the car and hold it wide open with the throttle and you will see. I have driven one, yes.

At low power setting the V'tronic is doing just that, limiting the valve lift to effect low power...by throttling the charge entering the cylinder AT THE VALVE instead of at the throttle blade. The piston sees the same force during the intake stroke and the total charge in the chamber is the same density as with a throttle. How do I know this....LOL.....because the engine idles and runs "part throttle" just like an engine with a throttle....sooo.....the power the engine is making is the same in those conditions and thus, according to the physics of a spark ignited gasoline engine the cylinder pressures are the same. The engine must be throttled some way to accomplish this and the pumping losses are the same in those conditions.

The idea that the V'tronic engine is not throttled just because it doesn't have throttle blades is completely wrong and misguided.....i.e..."there's much less or no throttling action in these modes because of the lack of a throttle plate" and " What such a system allows, as complex as it is, is for a drastic reduction in pumping losses", etc......... Sorry to be so rude but I have explained this concept away several times and you keep repeating it. The engine HAS to be throttled because it doesn't run away at idle. Something is throttling it....it is the low lift of the valve causing the severe restriction.



I suggest one of the major text books on the subject of Spark Ingnited Gasoline Engines by Taylor and Taylor for reference. When you find something in there that proves me wrong let me know....LOL.

Geez....even Googling VANOs and Valvetronic gives you more reading than you can accomplish in a lifetime that explains how the system works. And someone wonders how I know so much about it!!!???!!!


Dealing with the EPA with any sort of emission's package or control is full of problems and pitfalls. The diesel and DI and such folks are no different. They are just late to the game and think they are being singled out....LOL.

chevelle I must thank you and bbob for a most informative and entertaining thread. Thanks.

Thanks.

As a clearfication....In my haste to record the above thoughts I inadvertently interchanged Vanos and Valvetronic in some of my comments. I edited the most recent post for accuracy.

Vanos is the part of the BMW valve train system that adjusts the cam timing. Vanos is the name BMW uses to describe variable valve timing or VVT as most people call it. Vanos and DoubleVanos systems (Vanos on both the intake and exhaust cams) are on many BMW engines as are VVT sytems on most other premium engines. This (valvetronic) has nothing to do with throttling the engine, it just improves the torque curve characteristics.

Valvetronic is the part of the BMW valvetrain sytem that adjusts the valve lift and provides the throttling effect for the engine. This is completely independent of the Vanos system.

My bad. Sorry for the confusion.

Hay Chevelle,

Thanks for that long explanation. I did google for information and all I got were a bunch of useless reviews and marketing info. Just now, I went to sae.org and did a search on 'valvetronic' and 'vanos' and got a whole bunch of great stuff. Much better than a Google search. Thanks again for the suggestion. The hits I get from Google mention drastic reductions of pumping losses, but no engineering discussions - not enough to enlighten anybody on this board. I want to find out more about this.

You mention "Valvetronic basically alters the total valve lift to the point that at low loads the valve lift is very slight". This I did NOT know. This is the ONE piece of information I was looking for and could not find. I had always known that they're playing with the computer algorithms to 'throttle' the engine to some extent, but I didn't realize that at low power settings the valve lift was substantially less than a conventional valve train. According to your argument, they have accomplished zero in reducing pumping losses. Maybe this wasn't what they were trying to do. This is very interesting.

I suspect we may never see a system that has high-lift and long-duration at low power settings because doing so causes all sorts of side effects such has increased NOx and extreme lean operation. So, it looks like there does not exist a system that is anywhere near to the point where the pumping losses from throttling are drastically reduced in a gasoline engine. I was thinking that by eliminating the butterfly throttle, there would be *some* savings.

I understand that Vanos,Valvetronic, VVT, VTEC, etc are all about power, drivability, and efficiency. That's all interesting unto themselves but what I'm really interested in is current research into eliminating pumping losses in gasoline engines.

P.S. I tried to open the SAE papers and they want $12 for each paper. Dang it. Do you have other sources or actual papers that you can share? I'd appreciate it. I'm sure others would, too. Again, Google searches turn up items that give this subject only a superficial treatment. No real substance.

My question is if they were trying to reduce pumping losses, how much did they actually accomplish? That's what I've been trying to answer. Google didn't tell me and I can't get anything from SAE without paying a small fortune.

I found this link:

BMW World - Technology (http://www.bmwworld.com/technology/valvetronic.htm)

There, they mention that "because Valvetronic allows the engine to breathe more freely, fuel consumption is reduced by 10%.". They go on to say that Valvetronic "minimizes pumping loss by reducing valve lift and the amount of air entering the combustion chambers."

What the heck??!?!? it seems they're contradicting themselves. I wonder if that's a typo or the editor whacked out some important sentences.

Over the past few days, I've found a number of these articles that kinda say the same thing. Lots of words like "reduces pumping losses", but no explanation. No details. Following BMW's marketing line, perhaps.

Even Car and Driver Magazine toes the line. They even mention a specific increase in efficiency due to reduction in pumping losses - 12%. See Technical Highlights - Features - Car and Driver - April 2005 (http://www.caranddriver.com/features/9266/technical-highlights.html)

What up with this?

I had always known that they're playing with the computer algorithms to 'throttle' the engine to some extent,

I suspect we may never see a system that has high-lift and long-duration at low power settings because doing so causes all sorts of side effects such has increased NOx and extreme lean operation.

So, it looks like there does not exist a system that is anywhere near to the point where the pumping losses from throttling are drastically reduced in a gasoline engine. I was thinking that by eliminating the butterfly throttle, there would be *some* savings.

I understand that Vanos,Valvetronic, VVT, VTEC, etc are all about power, drivability, and efficiency. That's all interesting unto themselves but what I'm really interested in is current research into eliminating pumping losses in gasoline engines.


My question is if they were trying to reduce pumping losses, how much did they actually accomplish? That's what I've been trying to answer. Google didn't tell me and I can't get anything from SAE without paying a small fortune.



Computer algorithms alone do not throttle or unthrottle the engine. To change the throttling or pumping losses requires hardware changes to the engine. Computer algorithms are getting more and more refined at modeling exactly what an engine does or needs to do so as to provide the exact amount of fuel and spark advance to run the engine most efficiently at any given instant but the computer algorithms cannot create or eliminate pumping losses or effect throttling.

There are lots of systems with high lift and long duration at low loads.....LOL. Racing cams on cruise night are exactly that. With lots of lift and lots of duration at low loads you get tons of reversion and a very rough idle. The heavy lope from a hot cam is exactly what you are describing. It doesn't work very well in passenger car engines in daily use so that is why you don't see that very often.

To be honest the idea of the high lift and long duration doesn't make the engine run "lean" or "rich" per se. It just makes the engine such and inefficient air pump that the chamber is still full of exhaust byproducts and poor filling so the idle is rough and unstable. The engine is "throttled" in a way by this because the intake manifold vacuum is very low under those conditions (put a vacuum gauge on an engine with a big cam and you will see very low vacuum at idle and low speed) so, in effect, the idea of eliminating the throttle is partially accomplished but one cannot live with the side effects of the rough idle and unstable combustion. The instability drives up HC and CO to some extent but NOx is actually very low due to the fact that chamber temps and pressures are low with the high residual content and the high concentration of exhaust gases still in the chamber....built in EGR in effect.

There are two examples of systems in the market place that reduce pumping losses very effectively and successfully resulting in improved fuel economy due to the efficiency gained. The two systems are EGR and Displacement on Demand.

EGR on modern engines is used very effectively to reduce pumping losses by running very high levels of EGR. This is possible by designing the combustion chamber so as to have high EGR tolerance so it is capable of supporting stable combustion with a lot of EGR in the chamber. When the EGR levels can be dialed up this causes the intake manifold vacuum to drop when the EGR is applied thus reducing pumping losses. With modern control systems the correct spark advance can be delivered to offset the effects of EGR on combustion so the engine continues to run very efficiently and the resulting improvement in economy comes about due to the reduction in pumping loss. The engine is "throttled" in effect by feeding it lots of EGR so it is a perfect example of what you are describing regarding reducing pumping losses in a spark ignited gasoline engine.

The other example, DOD or the old Modulated Displacement on Cadillacs, cuts the engine displacement back severely under light load. The resulting smaller displacment engine has to be run nearer full throttle to make the necessary power desired so it is like a small 4 cylinder, for example, running nearly unthrottled. By unthrottling the engine (by opening the blade nearly wide open) there is little or no manifold vacuum so that directly reduces the pumping losses. The fundamental basis of DOD and why it works is reduced pumping losses, exactly what is being asked for.

The Valvetronic system results in a slight reduction in pumping losses by throttling directly at the valve and elminating the throttling at the throttle blade. There is always going to be flow loss or some level of throttling at the valve so with Valvetronic this becomes THE throttle. By then eliminating the throttle blade that additional flow loss or restriction is eliminated so there is a little gain but not a huge amount like a diesel manages to accomplish by throttling the engine purely with fuel.

I found this link:

BMW World - Technology (http://www.bmwworld.com/technology/valvetronic.htm)

There, they mention that "because Valvetronic allows the engine to breathe more freely, fuel consumption is reduced by 10%.". They go on to say that Valvetronic "minimizes pumping loss by reducing valve lift and the amount of air entering the combustion chambers."

What the heck??!?!? it seems they're contradicting themselves. I wonder if that's a typo or the editor whacked out some important sentences.

Over the past few days, I've found a number of these articles that kinda say the same thing. Lots of words like "reduces pumping losses", but no explanation. No details. Following BMW's marketing line, perhaps.

Even Car and Driver Magazine toes the line. They even mention a specific increase in efficiency due to reduction in pumping losses - 12%. See Technical Highlights - Features - Car and Driver - April 2005 (http://www.caranddriver.com/features/9266/technical-highlights.html)

What up with this?



The marketing guys will always pick up on some real or perceived gain with a high tech system and make hay with it. There is proabably some point in the engine operating conditions where the pumping losses might have been reduced by 10 or 12 percent on the BMW system. So the marketing guys use that number. It doesn't necessarily mean that Valvetronic reduces pumping losses that much under ALL operating conditions which is what is sort of being implied......

None of the magazines run tests to determine that sort of thing. They take the info from the BMW press kits that their marketing guys wrote and reword it for the articles. Most auto companies ghost write whole articles on things like Valvetronic and provide them in press kits. The publications just reword and rewrite portions where applicable and publish them. That is why a lot of what you read in the different car rags reads very similar. It was all written from the same PR info provided in the press kits.