How exactly does anti lag work and why does it make that distinctive noise?

 

From what I understand, it dumps petrol into the turbo in a special way so as to keep the thing spinning at peak boost, even at low revs. That's as much as I know, but someone else is bound to know more.

 

And eats through manifolds every 1000 miles

There has been a lengthy discussion of this topic before....do a search

 

In a nutshell!
by having the throttle butterfly partially open on "closed position"(No accel peddle) the engine allows intake air to enter on a trailing throttle,,,,so the air mixes with the fuel and ignites in the exhaust manifold.
(that's why it takes a few minutes to happen on a cold engine)
By controlling IGN, fuel and the amount the butterfly is open, this controls the amount of "anti lag" and hence boost is created.
(there is a WHOLE lot more of settings than just this)
(a recent client with MoTeC had the "AL" turned on after some driving and was simply amazed) pity more people don't run it for drag events, its amazing to drive a car with 10 - 15 psi BOOST at ZERO throttle!!!!! The turbo used in ALS equipped rally cars is smaller than you would see on a race car for two reasons. the first is that the FIA has a mandatory 34mm turbo inlet restrictor that limits air flow into the turbo, this means that it is pointless useing a large inlet turbine unit as the inlet could not flow any more air, secondly the lag would increase due to the inertia of the larger impeller. <I>courtesy of a previous post from John Felstead)</I>

I have some more technical descriptions about it if you want some?

Mike.

 

This is how it works.
Firstly, boost is controlled very acurately by using 2 fuel injectors as air valves, these feed the boost/atmospheric pressure to the waiste gate actuator, allowing minute and very fast acting boost control.
Secondly, the normal method of controlling engine iddle via an idle control valve, that bypasses the throtle butterfly is dispensed with, the static idle is set in the old fashioned way by a locked off bypass screw.
Thirdly, where the iddle control valve used to be, a new valve is fitted that has a solenoid controlled valve (looks like an engine inlet valve internally) that can open/close the throttle buterfly bypass orifice very qickly.
Forthly, a miram turbo shaft is used to withstand the massive increase in turbo temperature generated by ALS.
Fifth, there is no dump valve used on an ALS equipped engine, the whole point of ALS is to keep boosting the engine, even on closed throttle.
The way it works is that when you come off the throttle, for example braking hard into a corner, the throttle butterfly closes as per normal, once the boost drops to a certain level, the ECU starts to pulse the Throttle butterfly bypass valve, this has the same effect as you constantly stabbing the throttle on and off very quickly, this means that the engine is being driven by the ECU as though it wants to accelerate again, however this occilation of the throttle bypass valve is happening so fast, it has the effect of allowing the turbo to stay spinning yet produces no additional torque to drive the car forward.
The effect of all this is that massive heat is generated in the turbo exhaust side, which ignites all the excess fuel, there is no deliberate overfuelling going on to explode the turbo impellar area.
The most modern of ALS systems on the current world rally cars are far more efficient than a couple of years ago, which is why the ALS banging was less aparent this year on the RAC rally.
The turbo used in ALS equipped rally cars is smaller than you would see on a race car for two reasons. the first is that the FIA has a mandatory 34mm turbo inlet restrictor that limits air flow into the turbo, this means that it is pointless useing a large inlet turbine unit as the inlet could not flow any more air, secondly the lag would increase due to the inertia of the larger impeller.
The water injection system works by injecting a fine mist of water/air into the inlet plenum chamber when the boost/air charge temp reaches a certain level, the reason WI is used is to increase the effective octane rating of the fuel/air mixture to elliminate detonation, this allows far higher boost to be maintained, even in very hot climates.
This is not the same thing as intercooler sprays, these cool the external surfaces of the intercooler to help the cooling efficiency of the air/air intercooler.


scotland here we come, cya john

 

On group N cars, the air is taken from the Idle Speed Control valve, rather than the butterfly.

This can be mapped in from most aftermarket ECU's, such as Motec, GEMS and of course Link.

The explosions in the manifold do wonders for the life expectancy of the turbo and manifold

 

Blimey John, you typed that quickly!!

Spot on description of a WRC/group A car