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. |
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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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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"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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(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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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, 01:55 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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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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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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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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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.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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01-02-2014, 02:56 AM | #20 | |
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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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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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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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