BMW M3 and BMW M4 Forum - View Single Post - S55 anti-lag system

solstice · 01-01-2014, 10:44 PM

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."

01-01-2014, 10:44 PM	#6
solstice Major General 5458 Rep 7,037 Posts Drives: 2015 M3 6MT Join Date: May 2013 Location: Seattle iTrader: (0)	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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