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      01-01-2014, 02:33 PM   #1
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S55 anti-lag system

I thought it could be good to have a dedicated thread for this part of the S55 to post specifications, experience of similar systems, pros, cons etc.

I don't have personal experience of these kind of systems but would like to hear from those who have.

What I understand the S55's system is based upon that some fuel is pumped into a few (3?) cylinders off throttle to keep feeding the turbos with exhaust gases off throttle. There are a lot of questions around this. Will the tranny be in neutral without engine breaking? I.e sailing mode etc.
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      01-01-2014, 02:43 PM   #2
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Very good to see a new post. I look forward to seeing comments from various contributors who have a lot more experience on these issues, etc. Also, the other posts were getting stale (no offense to anyone) and it is great to see something new. I know the NAIAS is around the corner but there has been a paucity of new images and information (other colors shown would be nice and pricing details and options available).
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      01-01-2014, 03:56 PM   #3
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To quote myself and CanAutM3 from another thread that discussed the anti lag:

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Originally Posted by Boss330 View Post
With valvetronic, you can have better control of valves (I guess?). For instance creating a "blow through" situation where the injected fuel is ignited but the combustion pressure isn't trapped inside the combustion chamber but released through the exhaust valves (intake valves must be closed during this stage to avoid the pressure escaping to the intake manifold) and thereby spinning the turbos. Sort of like igniting fuel in a container with a small opening, creating a "jet stream" of hot air (exhaust). That "jet stream" will keep the turbos spinning at a high rpm (stated to be around 100.000rpm!!!). Since the combustion pressure is bled out through the exhaust valves, engine braking shouldn't be adversely affected perhaps?

And I also believe that this "jet stream" will be able to sustain a certain boost pressure even under deceleration. At least that would be beneficial in reducing lag, as otherwise the turbos will need time to raise pressure. With a "anti lag base pressure" of say 0.5bar, the engine would feel much more responsive and lag will be virtually non-existent.

For the cylinders that "participate" in the anti lag function this is how I imagine the system works:

Stage 1: Air enters combustion chamber (intake valves open, exhaust valves closed - intake stroke)
Stage 2: Air is compressed (intake and exhaust valves closed, creating engine braking - compression stroke)
Stage 3: Fuel is injected and spark is introduced (both intake and exhaust valves closed, or possibly starting to open exhaust valves here - combustion stroke)
Stage 4: Combustion starts and exhaust valves are opened to vent exhaust (intake valves closed, exhaust valves open - "exhaust stroke")

Stage 1-3 is equal to a normal 4-stroke combustion cycle
Stage 4 is different because the combustion energy isn't used to push down the piston, but to create a "jet stream" of exhaust gases to the turbos and spinning them.

Fuel injected in this "anti-lag" process is measured to create a combustion needed to spin the turbos, not the same amount of fuel needed to push down the piston in a normal 4-stroke cycle.


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Originally Posted by CanAutM3 View Post
Good analysis .

I agree that, with this feature, it is possible to keep the car "on boost" with "closed throttles". To achieve this, the intake valves would need to open as little as possible on a few cylinders (while remaining closed on others) to just sustain the exhaust "jet stream" you mention. With the intake valves mostly closed there is very little air flow into the engine and the turbos do not need to produce much work to maintain boost. By precisely adjusting the bleed off valve and Valvtronic, the turbo speed and boost pressure can be maintained.

It is very similar to an old driving technique I learned in rally school. Left foot brake to slow the car down but keep the right foot on the throttle to keep the turbo spinning and on boost (I know, there are other reasons to left foot brake but this is also one of them )
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      01-01-2014, 08:00 PM   #4
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Very clear, thank you. I missed this in the earlier post.
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      01-01-2014, 09:11 PM   #5
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Thanks Boss330. Are those facts or speculation? Either is interresting and it seems to be speculation from your wording but I just want to be clear I read you right.
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      01-01-2014, 10:44 PM   #6
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I read a few descriptions and discussions about anti-lag systems.
I found these comments by "Knurled UltraDork" enlightening:

http://grassrootsmotorsports.com/for...r/59948/page1/

"There's several different kinds of antilag, but the common thing among them is that they kill engine power when off boost so the engine has to run closer to atmospheric in order to not die. So basically there's no engine braking, and a lot of times the engine is actually fighting you when you're trying to slow down.

Bang-bang type systems do basically ignite fuel in the exhaust manifold, so you need a $5-10k turbo to last any time at all, and you'll still nuke them on a regular basis, along with exhaust manifolds and valves. This kind of system can actually build boost faster by letting OFF the throttle... The more friendly systems just jack the idle up and cut fuel to random cylinders, so you're still running the engine under no vacuum at "off throttle" and moving air through the engine, it's just not actively burning fuel solely to turn the turbo. Dig?

Nutshell - antilag is never actually lifting off the throttle, whether by driving style or by letting the computer do it for you."

"Really there is no such thing as a "street friendly" anti lag system because anti lag is supposed to be for cars that spend 95% of the time under boost and 5% of the time not, as opposed to street driving which is 1% of the time under boost.

Something I alluded to in my earlier posts, and I'll finish up on now: Key is tuning the engine so that it basically never runs under vacuum, keep air moving and the turbo spinning. This is impractical for use on the street... unless you're drive by wire with DI.

Many/most DI engines have the throttle wide open most of the time and control engine power with fuel, thanks to stratified charge. They're closer to spark ignited Diesels than traditional gasoline engines. Point is, modern engines already run under no vacuum most of the time, which is part of why turbo response on modern cars is so much better than it used to be... they already HAVE a soft form of antilag.

This is also probably why you see cars (ahem BMW) with fake engine sounds piped in. A lot of the engine sounds that we find pleasing are INTAKE sounds. You don't get pleasing intake sounds (in the driver-feedback sense) when the intake is WOT all the time, so they have to muffle out the real sounds and provide pleasing ones."
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      01-01-2014, 10:54 PM   #7
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Do we know if the S55's ALS will be constantly active in all modes and speeds? It would be cool ( and frankly required if we want to claim NA like throttle response ) but it's kind of an anti thesis to ass ( auto start stop ) to burn fuel off throttle so I kind of doubt it and also due to the time usually spent off boost ( cruising ) in street driving where I guess the system would need to do some work to keep boost constantly elevated.

Last edited by solstice; 01-01-2014 at 11:15 PM..
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      01-02-2014, 12:55 AM   #8
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I wonder if there is modified programming of the HDEV5.2 injectors to spray more fuel towards the end of the compression step instead of just some to lean out the fuel to air mixture that will enhance the antilag tactic. At this point the spray angles of the nozzle are adjusted to push the jet flow towards exhaust valves. Because of the solenoid injector mechanism and the design of combustion chamber the compression can be increased as the rpms climb due to the ability to cool off and better dissipate the fuel.
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      01-02-2014, 01:38 AM   #9
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Quote:
Originally Posted by solstice View Post
Do we know if the S55's ALS will be constantly active in all modes and speeds? It would be cool ( and frankly required if we want to claim NA like throttle response ) but it's kind of an anti thesis to ass ( auto start stop ) to burn fuel off throttle so I kind of doubt it and also due to the time usually spent off boost ( cruising ) in street driving where I guess the system would need to do some work to keep boost constantly elevated.
This is from a post by Jason:

"In "Sport" and "Sport Plus" settings, the turbochargers are "pre-tensioned," which means that they keep spinning at a high rate of speed even after you have taken your foot off the throttle. This trick ensures ultra-quick response times fully comparable to those of a naturally aspirated engine. To bring engine revs down, cylinders are deactivated. The system doesn't work for extended time, but it operates under racetrack conditions and whenever the car senses quick bursts of acceleration and deceleration."

http://f80.bimmerpost.com/forums/sho...d.php?t=893216

It seems whatever system they will be using does cause extra stress on the components which is why its not an always on thing.
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      01-02-2014, 01:38 AM   #10
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Quote:
Originally Posted by solstice View Post
Do we know if the S55's ALS will be constantly active in all modes and speeds? It would be cool ( and frankly required if we want to claim NA like throttle response ) but it's kind of an anti thesis to ass ( auto start stop ) to burn fuel off throttle so I kind of doubt it and also due to the time usually spent off boost ( cruising ) in street driving where I guess the system would need to do some work to keep boost constantly elevated.
From the official M3/M4 threads:

(Turbos) ◦Pre-tensioned in Sport and Sport+ modes (keep spinning at a high rate of speed even after throttle lift-off, for ultra quick response.

In "Sport" and "Sport Plus" settings, the turbochargers are "pre-tensioned," which means that they keep spinning at a high rate of speed even after you have taken your foot off the throttle. This trick ensures ultra-quick response times fully comparable to those of a naturally aspirated engine. To bring engine revs down, cylinders are deactivated. The system doesn't work for extended time, but it operates under racetrack conditions and whenever the car senses quick bursts of acceleration and deceleration.

http://f80.bimmerpost.com/forums/sho...d.php?t=893216
http://f80.bimmerpost.com/forums/sho...d.php?t=923203
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      01-02-2014, 01:50 AM   #11
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Quote:
Originally Posted by solstice View Post
I read a few descriptions and discussions about anti-lag systems.
I found these comments by "Knurled UltraDork" enlightening:

http://grassrootsmotorsports.com/for...r/59948/page1/


Many/most DI engines have the throttle wide open most of the time and control engine power with fuel, thanks to stratified charge. They're closer to spark ignited Diesels than traditional gasoline engines. Point is, modern engines already run under no vacuum most of the time, which is part of why turbo response on modern cars is so much better than it used to be... they already HAVE a soft form of antilag.

This is also probably why you see cars (ahem BMW) with fake engine sounds piped in. A lot of the engine sounds that we find pleasing are INTAKE sounds. You don't get pleasing intake sounds (in the driver-feedback sense) when the intake is WOT all the time, so they have to muffle out the real sounds and provide pleasing ones."
If the above was the case for BMW, then there would be no need for the complex and expensive valvetronic system...

Valvetronic has replaced the throttle valve on most (all) BMW petrol engines today. Valvetronic is a clever way to vary the valve lift on the intake side and thereby creating the air flow management that a normal throttle body valve does. On my N53B30 engine (with DI) there isn't space for valvetronic in the cylinder head and instead there is a regular throttle valve. Those DI engines that run "unthrottled" usually don't have a throttle body valve at all.
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      01-02-2014, 01:53 AM   #12
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If you wonder how a twin turbocharged BMW N55 feels like, then this review by Chris Harris on the Alpina B3 should give us a clue on throttle response

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      01-02-2014, 01:55 AM   #13
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Thanks, so it looks like it's mostly for track use or similar spirited driving conditions and not a system that will give us a constantly responsive engine. I.e turbo lag of N54 or maybe worse will be with us during our daily commutes. Oh we'll, it's kind of what I suspected anyway.
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      01-02-2014, 01:58 AM   #14
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Quote:
Originally Posted by Boss330 View Post
If you wonder how a twin turbocharged BMW N55 feels like, then this review by Chris Harris on the Alpina B3 should give us a clue on throttle response

I drove the new Alpina B7 on track and it's one the laggiest modern engines I've driven. Really awful on the track.
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      01-02-2014, 02:28 AM   #15
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Quote:
Originally Posted by solstice View Post
Thanks, so it looks like it's mostly for track use or similar spirited driving conditions and not a system that will give us a constantly responsive engine. I.e turbo lag of N54 or maybe worse will be with us during our daily commutes. Oh we'll, it's kind of what I suspected anyway.
Quote:
Originally Posted by solstice View Post
I drove the new Alpina B7 on track and it's one the laggiest modern engines I've driven. Really awful on the track.

Are you comparing a 7-series based Alpina B7 with the B3???

That's like comparing a M5 with a 750i... Or saying that "I have driven a Porsche 928, so I know how a 991 GT3 feels like"

Did you even view the video I posted and heard how someone who actually drove the B3 said it felt?
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      01-02-2014, 02:35 AM   #16
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Quote:
Originally Posted by Boss330 View Post
Are you comparing a 7-series based Alpina B7 with the B3???

That's like comparing a M5 with a 750i... Or saying that "I have driven a Porsche 928, so I know how a 991 GT3 feels like"

Did you even view the video I posted and heard how someone who actually drove the B3 said it felt?
Calm down. I watched the video but I only put so much value on these kind of reviews. CH is an entertainer like Jezza, I like him and his style of reviews but quite often disagree with him when I drive the cars.

I drove the B7 back to back with among others the 750il which had far superior throttle response and none were close to the M5/M6s. I'm therefore highly suspicious to the claims about the B3. Different engine but similar tuning of a BMW engine and I know the N55 very well.

When it comes to the S55, BMW obviously saw the need for an anti-lag system. A system that is only active in a narrow scenario. You can draw your own conclusions but I will expect and accept that we will see turbo lag.
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      01-02-2014, 02:38 AM   #17
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Quote:
Originally Posted by solstice View Post
Thanks, so it looks like it's mostly for track use or similar spirited driving conditions and not a system that will give us a constantly responsive engine. I.e turbo lag of N54 or maybe worse will be with us during our daily commutes. Oh we'll, it's kind of what I suspected anyway.
I would wager that it would be no worse than the N54 but very likely better. Remember that the N54 didn't have valvetronic and from what I've read it noticeably helps with responsiveness. Also I'd think that 7+ years of experience has helped BMW make an even more responsive turbo engine.
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      01-02-2014, 02:42 AM   #18
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So to get anti-lag we need to be in Sport or Sport Plus mode, no problem, one can probably have the M button set this automatically.

However, it appears there is an additional requirement and additional limitation.
Additional requirement: The brain of your car must also believe you are under "race-track" like conditions with bursts of significant acceleration and deceleration.

Additional limitation: The system can not work for an extended period of time.
Doesn't sound great. You can't have your cake (low displacement, lower cost, great fuel efficiency) and eat it too (NA throttle response). It's very likely going to be all about software! Surprise, surprise. What happens when cruising very mellow for many miles/minutes (no near term track/racing style driving history) and then you simply want to gun it for some fun or to face a challenger. Will this be lag-o-rama? It sounds like it will be to me. However, very clever software may help. Not sure how such instant on demand could be predicted though...
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      01-02-2014, 02:44 AM   #19
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Quote:
Originally Posted by johns View Post
I would wager that it would be no worse than the N54 but very likely better. Remember that the N54 didn't have valvetronic and from what I've read it noticeably helps with responsiveness. Also I'd think that 7+ years of experience has helped BMW make an even more responsive turbo engine.
I mostly agree but keep in mind that the S55 has far more boost than the N54 stock so the turbo attributed power is higher which might cancel out some of advances in tech. vs. the N54. I.e the time from zero to peak boost is likely longer when going to 18psi vs. 8psi.
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      01-02-2014, 02:56 AM   #20
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Quote:
Originally Posted by solstice View Post
I mostly agree but keep in mind that the S55 has far more boost than the N54 stock so the turbo attributed power is higher which might cancel out some of advances in tech. vs. the N54. I.e the time from zero to peak boost is likely longer when going to 18psi vs. 8psi.
That's a fair point. although the 18 PSI is an absolute max (over all temps and altitudes). So say nominally its closer to 14 PSI (complete guess) then couple that with the new tech/methods BMW is using to improve lag/responsiveness (new Mitsubishi turbos, Impulse charging, Flow-enhanced manifolds, Electric wastegate actuator) and maybe the disparity goes away.

One things for sure though, I'm definitely excited to hear some first hand accounts in a few months (hopefully).
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      01-02-2014, 03:17 AM   #21
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Quote:
Originally Posted by solstice View Post
Calm down. I watched the video but I only put so much value on these kind of reviews. CH is an entertainer like Jezza, I like him and his style of reviews but quite often disagree with him when I drive the cars.

I drove the B7 back to back with among others the 750il which had far superior throttle response and none were close to the M5/M6s. I'm therefore highly suspicious to the claims about the B3. Different engine but similar tuning of a BMW engine and I know the N55 very well.

When it comes to the S55, BMW obviously saw the need for an anti-lag system. A system that is only active in a narrow scenario. You can draw your own conclusions but I will expect and accept that we will see turbo lag.
The B3 has a very different engine from the N55 in a 335i. It has different CR, new engine management and not least it has TWO turbo's.

The B7 has the N63 engine with "enhanced" turbo's and a bit more boost... When and where did you drive the B7?
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      01-02-2014, 03:21 AM   #22
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Quote:
Originally Posted by swamp2 View Post
So to get anti-lag we need to be in Sport or Sport Plus mode, no problem, one can probably have the M button set this automatically.

However, it appears there is an additional requirement and additional limitation.
Additional requirement: The brain of your car must also believe you are under "race-track" like conditions with bursts of significant acceleration and deceleration.

Additional limitation: The system can not work for an extended period of time.
Doesn't sound great. You can't have your cake (low displacement, lower cost, great fuel efficiency) and eat it too (NA throttle response). It's very likely going to be all about software! Surprise, surprise. What happens when cruising very mellow for many miles/minutes (no near term track/racing style driving history) and then you simply want to gun it for some fun or to face a challenger. Will this be lag-o-rama? It sounds like it will be to me. However, very clever software may help. Not sure how such instant on demand could be predicted though...
Only time (and "real" driving) will tell how the S55 feels.

But to me, the Alpina B3 review from Chris Harris was interesting as that indicates a very responsive throttle on a car with the N55, twin turbo's and NO anti lag
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