S55 Anti Lag vs F1 "blown diffuser" tech - Possible explanation on S55 ALS?

[Boss330]

There has been some discussion and speculation on how the S55 Anti Lag System (ALS) operates.

I remembered that a few years back Formula 1 had a big debate on the "blown diffuser", where exhaust gases was exiting in the diffuser, thereby creating an added downforce by keeping air flow (or in this case, exhaust flow) through the diffuser. Of course this works great under throttle/acceleration, but on the overrun (engine braking) the exhaust flow disappears as the throttle valves close and no air is pumped through the engine and into the exhaust manifolds.

F1 engineers at used a loophole in the regulations and programmed the fly by wire throttle valves to be kept open also on the overrun (engine braking). This means that there is still airflow through the engine and into the exhaust manifolds. Various degrees of throttle opening was used by the different manufacturers.

The official line why they employed the open throttle on the overrun was to "cool the exhaust valves"...

Some teams/engine manufacturers used only "cold blowing" but others used "hot blowing". The difference between them being that the cold blowing only used the open throttle to allow air to be pumped through the engine, while hot blowing also employed fuel injection on the overrun. The fuel added, combined with retarding the ignition perhaps as much as 45 degrees, ignites in the hot exhaust manifolds and creates a hot exhaust gas going to the diffuser. Hot blowing creates a gas flow on the diffuser that is more similar to the gases under acceleration (hot exhaust gases).

Reading the technical manuals on the S55 I suspect that a similar strategy is used for the anti lag system. The valvetronic, or throttle valve, is kept open on the overrun (and most likely also on the upshifts on the DCT) creating a gas stream in the exhaust manifold also under engine braking. And thereby spooling the turbos/keeping the turbos spooled.

Whether the S55 uses cold blowing or hot blowing I'm not sure of. But BMW has said that fuel consumption increases when ALS is activated, suggesting that some form of hot blowing is taking place.

Listen to the second car in this video (Red Bull) and compare that to the "fart" created by the S55 at "off throttle" situations.

Here are some different blown diffuser sounds:

Here is a quite good article on the blown diffusers and how they achieved this concept:

http://www.formula1-dictionary.net/o...e_overrun.html

The brief history of it is that Charlie Whiting, head of the FIA technical department, feels that the use of exhaust gas to create downforce is illegal. This comes from the regulation change that bans the F-Duct, which says “no driver movement shall deliberately affect the aerodynamics of the car”. Clearly this involved driver movement (a foot lifting off the accelerator pedal).
Therefore any engine mapping with the prime purpose of using the engine as a thrust-producer is illegal. Charlie issued a series of technical directives to that intent culminating in a technical directive, which came to teams roughly two weeks ago, a bit before Valencia GP 2011. It said hot-blowing – ie fuelling and igniting on over-run – is banned and for cold-blowing – ie without injection and ignition – the maximum throttle opening would be 20 per cent at 18,000 rpm tapering to 10 per cent at 12,000 rpm.

It seems that Mercedes in particular lobbied that they should be able to retain over-run (with zero pedal) fired by 4 cylinders (half the cylinders in an F1 engine). They persuaded Charlie they were doing that in 2009 for the prime purpose of brake balance modification and therefore should be allowed to continue doing so for reliability reasons. Charlie’s philosophy is that things teams did prior to using the exhaust to create downforce should still be legal. So Charlie agreed to what Mercedes requested.

Renault engines had been operating from 2009 with a strategy of running throttles 50 per cent open (so called cold-blowing) on over-run for reasons of throttle response and engine braking balance. As this was also for non-downforce generating reasons, Renault believed they should be allowed to continue doing it, for the same reason Mercedes were allowed to continue hot-blowing. So Charlie agreed to allow 50% of throttle opening for Renault.

But Renault’s rivals object because the French engine company has now been allowed to have a 50% throttle opening when the driver is lifting the throttle.
This is what Whitmarsh calls “a very substantial performance benefit”. To which Horner responds: “Why is it any more of a performance benefit than fired overrun?”

Leading Formula One engineers have spoken out about the influence of cold and hot blown diffusers, and how their teams have had to adopt their cars for the upcoming rule change. As I can see, a lot of fans on forums think that this is a quite simple thing of matter to change these configurations of engine mappings. No problem, change a few parameters and things is done.

But it's not that simple, and it affects how you operate the engine.

We need to understand what is going on within the engine when a driver lifts off the throttle and the subsequent effect that has on other aspects of the car. Unlike in road cars the driver in an F1 car does not leisurely lift off the throttle and delay the braking phase. Instead the driver may be at near maximum revs, when he will simultaneously lift off the throttle pedal completely and hit the brake pedal hard for the initial downforce aided braking. During the braking, the lower gears will be sequentially selected, further peaking revs all the time as the car slows down. This sudden closing of the throttles blocks the inlet to the combustion chamber, but the pistons in the cylinders will continue to pump up and down at a great speed. This creates huge stresses inside the combustion chamber and the vacuum created will suck air past the piston rings (so called blow-by). This will rapidly slow the engine, creating too much engine braking effect, which in turns creates stresses in the drive train and over-brakes the engine. The excessive engine braking effect will make the car nervous on throttle lift off, regardless of any subsequent aerodynamic effect. So engine manufacturers find different solutions to ease the stresses and braking effect of the driver lifting off the throttle.
In the past there were several different engine strategies in place and the driver was able to change overrun setting to tunes the cars handling, and driver switching between teams found the change in overrun settings needed some adjustment to both their driving style and sometimes with the engines settings.

Renault engine for example runs open throttles on the overrun (but no fuel injected or spark), this both eases the blow-by, reducing the vacuum effect inside the pistons and stress issues, it also useful for cooling the exhaust valves, as a great alternative to using excess fuel to cool the back of the valve. Renault sport is believed to be running as much as 90% open throttle on the overrun. This is what's best known as cold-blown mapping. During this season and through out free practice, the three Renault engined teams, had a distinctive loud overrun note, which continues briefly as the drivers picked up the throttle out of slow turns. As the throttles are open more than other teams, the induction noise is far greater.

Mercedes have their solution, this is the so called fired or hot overrun. When the driver lifts off, fuel continues to be injected into the engine and spark fired within the combustion chamber but ignition was delayed as much as 45%. This offsets the engine braking effect created by the engine, giving a smoother transition from on throttle to the overrun when off it and again reducing the vacuum effect inside the pistons and stress issues. As a result this means there is less engine braking effect. This gives Mercedes the freedom to define braking bias and KERS charging, without having to account for engine braking. Effectively decoupling the engine braking effect from the actual action of the braking system. As with Renault's mapping in past times, Mercedes solution is analogous to the hot blowing mapping. At pre Silverstone free practices and races, Mercedes engined teams had a particularly clean overrun sound. Where as Ferrari had far more cracks and pops as the engine slowed.

Cosworth are using same system as Renault to ease stresses on their engines and transmissions.


With all engine manufacturers having long established overrun strategies that have critical impacts on the basic engine design or the braking system, it was hard to rapidly switch to a very strict overrun mapping as demanded by the blown diffuser rule after Valencia GP race 2011. Renault and Mercedes lobbied the FIA to be allowed to retain elements of these old overrun strategies, while still emasculating their current strategies. The FIA have been able to see the mappings used in 2009 through to the current day, as the ECU code is held by the FIA since the advent of the single ECU. They've been able to see the engines have had these long established mappings, but also how they have become more aggressive since the "Blown Diffuser"has been developed.

So the FIA relented. This sounds like a climb down by the FIA and unfair to different engine manufacturers. But the unreported events at Silverstone are fairer than the picture being painted by the teams and the media. Its true that Renault were given their greater throttle opening, but also Mercedes were given their fired-overrun, but these dispensations have been given to every engine manufacturer, so Ferrari could have more throttle opening or Cosworth could develop a fired overrun.

An article more about the diffuser concepts, but with a good explanation on hot and cold blowing:

http://www.formula1-dictionary.net/diffuser_blown.html

Cold blowing – Normally the engine will only produce enough exhaust gases when the driver is on the throttle. This means when the driver lifts off, the blown diffuser is suddenly robbed of the additional airflow. To improve the situation, some teams get an idea. When the driver lifts off the throttle pedal the engine throttles go to 100% open and it cuts all the fuel and the spark, so there is no drive from the engine but all the air is flowing through the engine to give about 75% of the exhaust pressure you get on the power. Now engine is running as air pump. The exhaust is still ‘blowing’ into the diffuser, but that airflow is ‘cold’ since no fuel or ignition are involved. Everyone has been doing this for the last 12 months.

Hot blowing – For the last two or three months some teams have taken things a step further. In hot blowing they cut the ignition when the driver lifts off the throttle, but continue to inject some fuel through the engine’s valves into the exhaust to increase the energy into the gas. This fuel is not igniting inside the engine cylinders, but pass trough and ignites on the hot exhaust, increasing the amount, speed and temperature of the airflow exiting towards the diffuser. So they end up with more downforce. To do that they have to retard the ignition and kill the torque, because if you don’t then the engine is going to create torque and the engine is going to keep going when the driver lifts off the throttle. Clever engine maps prevent the engine pushing the car on in these conditions by retarding the ignition by as much as 35-40% on the over-run. By retarding the ignition when the driver lifts off, the fuel is no longer burnt inside a closed combustion chamber, but instead the fuel and air burn in the exhaust pipe, the expanding gasses blow out of the exhaust exit as though the engine is running . This creates a more constant flow of exhaust gasses between on and off throttle. This maintains the performance of the blown diffuser and keeps the downforce up when it's most needed. In this way they managed to avoid the main problem of an exhaust blown diffuser whereby when a driver lifts off the throttle for a corner, the downforce goes missing when you most need it and the rear stability changes.

It's not something you can do for all duration of the race as the engine temperatures go sky high, which damages the engine, but it gives that vital fraction of a second which keeps Red Bull ahead of the rest in qualifying. The problem here is that the engine mapping uses more fuel and creates excessive heat in the exhaust pipes and at the exhaust valve. Renault reported that both Red Bull and Renault used 10% more fuel in Melbourne compared to last year, most likely due to these off-throttle mappings.

[Blksnowflake]

Wow, awesome post. Thank you for taking the time. This makes you really miss the old F1 sounds, spine tingling.
Hopefully the retards don't turn this thread into a bashfest of the new F1 cars.

[MNoob]

18,000 rpm. Crazy.

[Boss330]

Originally Posted by MNoob

18,000 rpm. Crazy.

I know...

I actually visited Cosworth in 2004, when they where developing the V8 that they raced at 20.000rpm in the 2005 season. I was in their dyno room when one of the first prototypes was running...

[Acree]

Dang. Nailed it.

Great post.

[Dweezil]

great post and thanks for spending the time. Bring back the big V10's. There is not enough room on this server to handle the bashing of the new turbo 6 in F1 compared to the older NA cars.

[CanAutM3]

Originally Posted by Dweezil

great post and thanks for spending the time. Bring back the big V10's. There is not enough room on this server to handle the bashing of the new turbo 6 in F1 compared to the older NA cars.

I would not consider 3 liters a "big" engine. But I get what you mean .

[Boss330]

Originally Posted by Dweezil

great post and thanks for spending the time. Bring back the big V10's. There is not enough room on this server to handle the bashing of the new turbo 6 in F1 compared to the older NA cars.

Just to clear things up, those engines in the links was all the 2,4l V8

[Boss330]

Originally Posted by Railgun

Should be easy enough to find out really.

Explains a bit of delay in feeling engine braking on decel.

I would assume that it should be quite easy to find out by datalogging via the OBD.

I guess all you need to datalog is:

MAF
Ign timing
Fuel consumption

If mass air flow is still quite high on the overrun then that means the engine is still pumping air through it and feeds the turbo.

If fuel consumption is not at zero on the overrun then some fuel is also injected.

Of course it's not nearly as aggressive as on the F1 engines since there isn't that constant farting sound on the overrun etc.

Datalogging can be done by a simple app like DashCmd on your iPhone and by using a OBD dongle with a wifi connection to your iPhone (or via Bluetooth if you have a android phone).

[CaryTheLabelGuy]

Yes, I have already confirmed the S55 is using this method as a form of ALS. The remaining question is how much, if any, fuel is injected during these ALS events. I suspect, from extensive datalogging, that there is a slight amount of fuel from the injectors on the overrun delay. If there is fuel, it isn't much (I.e. The delay time is very short and not a lot of fuel is injected). I cannot datalog fuel injector pulse width to know for sure (which is all you need to datalog to know for sure, BTW). Ignition timing goes well south of "0" during these events as well. I can't tell how far below 0* the DME is pulling timing, however, as the datalogs don't log below 0*.

[Boss330]

Originally Posted by CaryTheLabelGuy

Yes, I have already confirmed the S55 is using this method as a form of ALS. The remaining question is how much, if any, fuel is injected during these ALS events. I suspect, from extensive datalogging, that there is a slight amount of fuel from the injectors on the overrun delay. If there is fuel, it isn't much (I.e. The delay time is very short and not a lot of fuel is injected). I cannot datalog fuel injector pulse width to know for sure (which is all you need to datalog to know for sure, BTW). Ignition timing goes well south of "0" during these events as well. I can't tell how far below 0* the DME is pulling timing, however, as the datalogs don't log below 0*.

That's interesting

Have you logged MAF to see how much air, if any, that is pumped through the engine in these situations?

It might not be the same method as the F1 engines used, but it would be interesting to see if the S55 keeps throttle partially open (or use valvetronic) to pump air through the engine, like the F1 engines did, and how much air is going through it if so.

On my DashCmd app which, is just a handy and easy to use, not a pro datalogging tool, I get ignition timing below 0 deg. I also get fuel consumption and fuel flow, which should at least give a slight indication of fuelling.

[CaryTheLabelGuy]

Originally Posted by Boss330

That's interesting

Have you logged MAF to see how much air, if any, that is pumped through the engine in these situations?

It might not be the same method as the F1 engines used, but it would be interesting to see if the S55 keeps throttle partially open (or use valvetronic) to pump air through the engine, like the F1 engines did, and how much air is going through it if so.

I detailed how I thought the ALS worked on the S55 based on my observations in another thread last week.

Yes, the throttle plate is remaining open during these ALS events, it is clear as can be in the datalogs. I cannot log MAF, unfortunately. Terry at BMS doesn't give the ability to log MAF but MAF isn't really all that relevant to the question as we already know for sure the throttle plate is remaining open. The real question is how much, if any, fuel is being injected during the ALS events. I am trying to get ahold of a factory scan tool to see what I can observe during these events to finally put this question to bed.

I'd also like to see how the DME is altering cam angle as well as what Valvetronic is doing during these events as well.

[Boss330]

Originally Posted by CaryTheLabelGuy

I detailed how I thought the ALS worked on the S55 based on my observations in another thread last week.

Yes, the throttle plate is remaining open during these ALS events, it is clear as can be in the datalogs. I cannot log MAF, unfortunately. Terry at BMS doesn't give the ability to log MAF but MAF isn't really all that relevant to the question as we already know for sure the throttle plate is remaining open. The real question is how much, if any, fuel is being injected during the ALS events. I am trying to get ahold of a factory scan tool to see what I can observe during these events to finally put this question to bed.

I'd also like to see how the DME is altering cam angle as well as what Valvetronic is doing during these events as well.

As regards the throttle valve, have you checked out if it is opening in relation to accelerator pedal position during regular driving?

Reason I'm asking is that on valvetronic engines it's usually intake valve lift that regulates air flow, the throttle valve is there just as a back up if valvetronic should fail. As I am sure you know, valvetronic varies intake valve lift, acting like a throttle valve. Lift can be varied from between 0,300mm at idle, and on the overrun, to full lift of 2,5-3mm (which I guess varies between engine types). And some direct fuel injected engines also run under what is called a stratified charge. Stratified charge is a condition where there is a surplus of air compared to fuel, the throttle valve is usually completely open under these conditions. In effect the engine operates like a diesel engine with excess air and open throttle. It's the amount of injected fuel that regulates the power output.

As we all know, fuel and air needs to be at a stochiometric ratio to ignite, so how can a direct injection engine run with a air/fuel ratio of 20:1 and higher? This is the beauty of direct injection, when fuel is injected directly in the combustion chamber. They manage to create a pocket of air/fuel where there is a stochiometric mixture.

My point is that a open throttle on a direct fuel injected engine, and especially on a valvetronic engine, doesn't necessarily mean that much...

Could you possibly check if the throttle valve isn't open at all times?

And even with a fully open throttle valve on the S55, it doesn't mean there is airflow through the engine. Valvetronic could be at minimum valve lift on the intake valves and thereby cutting airflow...

MAF is a very important factor in my opinion to figure out to which extent the S55 uses this feature, if at all.

[CaryTheLabelGuy]

I didn't see this post until now and I never addressed it when it was posted. So here goes:

Originally Posted by Boss330

As regards the throttle valve, have you checked out if it is opening in relation to accelerator pedal position during regular driving?

Being that this is a Valvetronic engine, the throttle plate has some strange behaviors as it attempts to regulate boost in concert with the EWGs. The throttle plate does open in relation to pedal input at partial throttle and light loads. However, once you enter medium to high loads and the engine starts to build significant amounts of boost, the throttle plate will open and close as it sees fit to help control boost entering the engine, past the throttle plate itself. So while you might see a spike in boost as measured before the plenum, the engine itself isn't necessarily consuming that much boost. You can be at full boost, WOT and the throttle plate might start closing up as much as 50% or so.

Originally Posted by Boss330

Reason I'm asking is that on valvetronic engines it's usually intake valve lift that regulates air flow, the throttle valve is there just as a back up if valvetronic should fail. As I am sure you know, valvetronic varies intake valve lift, acting like a throttle valve. Lift can be varied from between 0,300mm at idle, and on the overrun, to full lift of 2,5-3mm (which I guess varies between engine types). And some direct fuel injected engines also run under what is called a stratified charge. Stratified charge is a condition where there is a surplus of air compared to fuel, the throttle valve is usually completely open under these conditions. In effect the engine operates like a diesel engine with excess air and open throttle. It's the amount of injected fuel that regulates the power output.

As we all know, fuel and air needs to be at a stochiometric ratio to ignite, so how can a direct injection engine run with a air/fuel ratio of 20:1 and higher? This is the beauty of direct injection, when fuel is injected directly in the combustion chamber. They manage to create a pocket of air/fuel where there is a stochiometric mixture.

Your description of DI and Stratified Charge are correct. However, Air/Fuel mixtures can ignite leaner than Stochiometric (14.7:1 for pump gas and most race fuels) even in non-Direct Injection engines at idle and very light throttle, without any damage, especially on a modern non-DI engine. I routinely tuned Mitsubishi Evolution's (4G63) as lean as 18 to 20:1 at idle and light throttle as well as the K-Series Honda engines without any issue or misfires and most of those engines are still running on my tunes today without any issues or damage, including my personal Evo VIII. The 2JZ Supras I tuned didn't tolerate such lean mixtures at idle and light loads, but could easily tolerate 16.0:1, especially at idle. Tuning at such lean mixtures does increase NOx emissions, however.

As for the S55 and N55, they run normal 14.7:1 AFRs (stochiometric). I've never once observed my S55, for instance, run leaner than 14.7 once AFR stabilized at light and medium loads as well as idle. Some DI engines do utilize stratified charge like the Mitsubishi GDI, for instance. Stratified Charge is mostly used in N/A engines, however.

Originally Posted by Boss330

point is that a open throttle on a direct fuel injected engine, and especially on a valvetronic engine, doesn't necessarily mean that much...

Could you possibly check if the throttle valve isn't open at all times?

And even with a fully open throttle valve on the S55, it doesn't mean there is airflow through the engine. Valvetronic could be at minimum valve lift on the intake valves and thereby cutting airflow...

This is true. The throttle valve is never 100% closed (even at idle, where Valvetronic is used heavily to stabilize idle RPM), but it does open significantly on throttle (pedal) lift-off while in significant boost. There is also usually a boost spike as measured in the plenum just after lift-off followed by a very gradual decrease in boost, which leads me to believe that the engine, through Valvetronic and an open throttle valve, is blowing the boost charge through the engine using either cold or hot blowing (at least in Sport+ I believe fuel is injected, thus making it hot blowing ALS). This explains the burps or "farts" we all hear on lift-off.

[Boss330]

Originally Posted by CaryTheLabelGuy

I didn't see this post until now and I never addressed it when it was posted. So here goes:

Being that this is a Valvetronic engine, the throttle plate has some strange behaviors as it attempts to regulate boost in concert with the EWGs. The throttle plate does open in relation to pedal input at partial throttle and light loads. However, once you enter medium to high loads and the engine starts to build significant amounts of boost, the throttle plate will open and close as it sees fit to help control boost entering the engine, past the throttle plate itself. So while you might see a spike in boost as measured before the plenum, the engine itself isn't necessarily consuming that much boost. You can be at full boost, WOT and the throttle plate might start closing up as much as 50% or so.

Your description of DI and Stratified Charge are correct. However, Air/Fuel mixtures can ignite leaner than Stochiometric (14.7:1 for pump gas and most race fuels) even in non-Direct Injection engines at idle and very light throttle, without any damage, especially on a modern non-DI engine. I routinely tuned Mitsubishi Evolution's (4G63) as lean as 18 to 20:1 at idle and light throttle as well as the K-Series Honda engines without any issue or misfires and most of those engines are still running on my tunes today without any issues or damage, including my personal Evo VIII. The 2JZ Supras I tuned didn't tolerate such lean mixtures at idle and light loads, but could easily tolerate 16.0:1, especially at idle. Tuning at such lean mixtures does increase NOx emissions, however.

As for the S55 and N55, they run normal 14.7:1 AFRs (stochiometric). I've never once observed my S55, for instance, run leaner than 14.7 once AFR stabilized at light and medium loads as well as idle. Some DI engines do utilize stratified charge like the Mitsubishi GDI, for instance. Stratified Charge is mostly used in N/A engines, however.

This is true. The throttle valve is never 100% closed (even at idle, where Valvetronic is used heavily to stabilize idle RPM), but it does open significantly on throttle (pedal) lift-off while in significant boost. There is also usually a boost spike as measured in the plenum just after lift-off followed by a very gradual decrease in boost, which leads me to believe that the engine, through Valvetronic and an open throttle valve, is blowing the boost charge through the engine using either cold or hot blowing (at least in Sport+ I believe fuel is injected, thus making it hot blowing ALS). This explains the burps or "farts" we all hear on lift-off.

Thanks for taking the time to log the "odd" behaviour of the throttle plate. Interesting stuff indeed!

[Boss330]

Just read an article about the facelifted Porsche 911 Turbo S.

One of the changes was to increase throttle response and is called "dynamic boost". Under dynamic boost the throttle valve stays open for up to two seconds after the driver lifts off the throttle pedal.

So, Porsche now definitely use "cold blowing" as a method to decrease turbo lag/increase throttle response.

[CaryTheLabelGuy]

Originally Posted by Boss330

Just read an article about the facelifted Porsche 911 Turbo S.

One of the changes was to increase throttle response and is called "dynamic boost". Under dynamic boost the throttle valve stays open for up to two seconds after the driver lifts off the throttle pedal.

So, Porsche now definitely use "cold blowing" as a method to decrease turbo lag/increase throttle response.

Awesome. Thanks for the info. Can you link to the article? I'd love to read it.

Thanks.

[Boss330]

Originally Posted by CaryTheLabelGuy

Awesome. Thanks for the info. Can you link to the article? I'd love to read it.

Thanks.

It's in the last edition of EVO mag. The article isn't online...

But I found this press release from Porsche:

http://press.porsche.com/news/release.php?id=963

[terahertz]

Originally Posted by Boss330

It's in the last edition of EVO mag. The article isn't online...

But I found this press release from Porsche:

http://press.porsche.com/news/release.php?id=963

Depending on how you interpret "interrupting fuel injection", it could mean hot blowing on every other cylinder as well.

[Boss330]

Originally Posted by terahertz

Depending on how you interpret "interrupting fuel injection", it could mean hot blowing on every other cylinder as well.

Agree!

That part wasn't mentioned in the EVO article, so I didn't pick up that piece there.

[Who's on first]

Originally Posted by MNoob

18,000 rpm. Crazy.

No .. what's crazy was Ferrari was doing over 20K, before regulations started pulling them back. The true good old days, of our generation .. 03'-04'05' ..now that was a sound you never forget.

[RSXDC5]

Originally Posted by Boss330

There has been some discussion and speculation on how the S55 Anti Lag System (ALS) operates.

I remembered that a few years back Formula 1 had a big debate on the "blown diffuser", where exhaust gases was exiting in the diffuser, thereby creating an added downforce by keeping air flow (or in this case, exhaust flow) through the diffuser. Of course this works great under throttle/acceleration, but on the overrun (engine braking) the exhaust flow disappears as the throttle valves close and no air is pumped through the engine and into the exhaust manifolds.

F1 engineers at used a loophole in the regulations and programmed the fly by wire throttle valves to be kept open also on the overrun (engine braking). This means that there is still airflow through the engine and into the exhaust manifolds. Various degrees of throttle opening was used by the different manufacturers.

The official line why they employed the open throttle on the overrun was to "cool the exhaust valves"...

Some teams/engine manufacturers used only "cold blowing" but others used "hot blowing". The difference between them being that the cold blowing only used the open throttle to allow air to be pumped through the engine, while hot blowing also employed fuel injection on the overrun. The fuel added, combined with retarding the ignition perhaps as much as 45 degrees, ignites in the hot exhaust manifolds and creates a hot exhaust gas going to the diffuser. Hot blowing creates a gas flow on the diffuser that is more similar to the gases under acceleration (hot exhaust gases).

Reading the technical manuals on the S55 I suspect that a similar strategy is used for the anti lag system. The valvetronic, or throttle valve, is kept open on the overrun (and most likely also on the upshifts on the DCT) creating a gas stream in the exhaust manifold also under engine braking. And thereby spooling the turbos/keeping the turbos spooled.

Whether the S55 uses cold blowing or hot blowing I'm not sure of. But BMW has said that fuel consumption increases when ALS is activated, suggesting that some form of hot blowing is taking place.

Listen to the second car in this video (Red Bull) and compare that to the "fart" created by the S55 at "off throttle" situations.

Here are some different blown diffuser sounds:

Here is a quite good article on the blown diffusers and how they achieved this concept:

http://www.formula1-dictionary.net/o...e_overrun.html




An article more about the diffuser concepts, but with a good explanation on hot and cold blowing:

http://www.formula1-dictionary.net/diffuser_blown.html

Cool thought, but in short, the answer is no. That will not work on our cars. They are completely different executions of an antilag concept.