Anti Lag Systems - possible to reduce turbo damage? 3

[fireslave]

Ok, basically anti-lag systems are impractical because they are loud, and they destroy turbochargers.

I know that the "pulses" of the explosions shock the turbochargers, and that is what causes the damage.

The way to make it a more reliable system, then, would be to change a few large pulses into many small pulses.


Ok, so when you listen to an ALS equipped car, you hear a few explosions every second -
here's my question?
does the ALS system affect each combustion event to a small degree, or is it designed to affect a few to a large degree.

for example, i could make a simple ALS by just cutting one of every 10 sparks, or whatever, and then 1/10th of the air/fuel would explode in the exhaust manfold (due to heat, it ignites), spooling the turbo.

It seems like this is what happens... hence the pop-pop-pop... but that could just be fuel accumulating in the exhaust and then detonating.

the other method is to retard the spark - ignite the mix in the cylinder, but open the exhaust valve while its still burning. Now, initially i was like hmmm... just vent 10% of each event into the manifold and presto, boost!
but then i realized it would require much more precision to vent 10% of each event into the manifold, as opposed to venting 100% (not really 100, whatever, just BS numbers) of the explosiveness from 10% of events... hmmm... pop-pop-pop.

do any of you guys know how the various systems work in practice?



Also, i was on youtube, and I saw this:

http://www.youtube.com/watch?v=469mi4UOVK0

it sounds like its got some compressor surge going on (1:15)
its also got anti-lag (1:55) which, is in total opposition to any car that would have compressor surge... so it got me wondering what the hell is going on under the hood of this thing... is it venting the BOV air back into the turbine or something? it would flow through it, make a crazy noise, increase boost, but it could also meet the rich air from the exhaust, and therefore combust - producing anti lag perhaps?
I dunno. that cars intense, maybe the BOV is just a gimmick, but the car seems pretty well engineered, so i doubt it.

 

[fireslave]

the point of this is if there are a few large pulses and that's why the turbos break, you could deisgn the system differently so there were more small pulses (say one per spark event) and that would reduce stress on the turbo.

of course, if there are already 1-pulse-per-spark-event ALS systems and they still destroy turbos, my plan is pretty much shot...

thanks

 

[patprimmer]

My favorite anti lag system is Nos injection.

My second favorite is a drive belt.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[vagman2]

... is it venting the BOV air back into the turbine or something?

Yeah, when you lift up throttle I think they vent the compressed air through a controlled air valve(like an EGR valve) back in the exhaust manifold, plus 30-40deg timing retard. That's how they supply the air for the post combustion without keeping the throttle open or using a bypass air valve. This method is good because it keeps the engine brake function alive.

 

[izzmus]

I was always under the impression that turbo failure was due to excessive heat, given that exhaust valves and manifolds also tend to live short lives.

Audi pioneered a recirculating-air system ("Umluft") on their Group B car, and even that was destroying everything related to exhaust. From the descriptions, it sounds like they may have been jacking the throttle as well.

 

[vagman2]

This is the Audi S1 setup:

 

[fireslave]

thanks for the pic

i see there is a vacuum hose leading from the high pressure side of the compressor to the ALS valve... does it just open like a BOV, referencing both upstream and downstream of the throttle body?

Since the ALS is only active when the throttle bodies are close to the closed postion, it would make sense that the compressor outle side of the turbo would have higher pressure than the exhaust manifold, so the air would naturally flow in.
but after it detonates, i would think that the exhaust manifold would have higher pressure... are there 1 way values required to make this work?

do any of you guys know what the air pressure is in the manifold when its 'trapped' between the exhaust ports and a turbocharger? I would think that for, say 10 psi of steady boost, the mainfold pressure would be atleast twice that. My resoning being that turbochargers cant magically create boost without force...
now in my head, if there are indeed 1 way valves, this would crete an oscillating effect...
valves open
*bang*
valves close
pressure escapes
valves open
*bang*
valves close
pressure escapes
etc...

thanks for the help

 

[Deltona]

I think the sound when he backs off at 1:15 is that of an engine without a dump valve.

 

[fireslave]

so does anyone know how the air gets into the exhaust mainfold?

is the intake manifold pressure just always higher? (i doubt it)

or is there some sort of open-close effect after the pressure from each explosion disperses?

 

[vagman2]

This is the Subaru WRC setup (as I know). The air should be coming from the FMIC through that alu valve down to the collector pipe:

 

[BrianGar]

Check out this for serious anti lag!

http://www.youtube.com/watch?v=mXfUbFR-x7g