I've been driving turbo cars for years, but I've never heard of anti-lag, other than ways to combat lag with downpipes, etc. How can you beat lag with a computer? Is this kind of thing applicable to other turbo'd cars?

ALS is a complex system, 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 idle 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 ignition timing is also controlled during this off throttle period to again reduce torque yet maintain boost presure.
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 WRC rallies.
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 hope that helps a little.

great post john...

*jaw open* umm, wow, good post John! I was gonna say "urrrrrr, Mungo think anti-lag keep boost up!" but bravo on a much better job that I could've done!:)

A reasonably good post.. ;)

But..

Injectors (air injectors) dont have to be used... they are just specced by Ahmed/Harvey for the Cossie engine...

The stock boost solenoid will work fine (and in a lot of cases has to be retained to meet Grp N regs).

Some ALS's use the Air idle valve for antilag.. hence you can get air into the system with the throttle closed (when they dont have a screw). Although some do utilise throttle stops or extra valves due to limitations of the flow through the AIC valve.

A miram shaft is a nice touch.. but again.. isnt always required. But using an EGT probe in the turbo closed loop ALS can be incorporated with monitors and controls the agression of the ALS but maintain temperatures. The Pectel ECU supports this, and the Motec and be "tailored" to do this too.

Another point is that you lose your power assitance for your brakes (requires a vaccuum to operate).

But apart from the above... a great description

:)

J.

My description is how the GroupA and WRC full spec systems work. This is what MSport and Mountune use in the WRC.

You cant use normal amal type valves to give you the boost control required for groupA maps, they arent acurate enough and cannot pulse fast enough to give the boost ramps needed. Thats why 2 fuel injectors are used as air valves.

No serious rally car uses vacumn assisted barkes as you lose all feel from the braking system.

If you want a basic road car ALS system then you can get away with using some stock parts. I dont class that as ALS because its effects are minor compaired to WRC spec systems.

A WRC/GroupA rally car turbo would not survive without the Miram shaft. If you want ALS for your road car you may get away without that, but like i say, thats not real ALS, not even close.

Some designs do use stepper motors to activate the throttle buterfly by i find these over complicated. The 1st generation Escort WRC car used 2 bypass valves, the groupA Escort uses one bypass valve.

Attached is what a modified idle control valve looks like. The internals are completely removed and a steel valve is machined, this slides on a stainless steel pin (its stainless so it doesnt get magnatised by the solonoid).

above is the closed position, bellow is the open position.

and this is the valve in place on the inlet plenum of my rally teams Escort Cosworth GroupA rally car engine.

I found it interesting that the Audi R8 employed ALS starting this year at Sebring I believe. Not only on heavy braking/down-shifts (sequential Ricardo transmission) but also on upshifts at high speed. Funny, at Petit Le Mans last weekend Cadillac could be heard to have followed suit :)


James

The WRC cars also use startline ALS systems.

You go through a startline sequence, primed at 5 seconds before setting off that brings the boost right up for a quick launch.

You can sort of do this with the older ALS systems but the launch control systems are pretty brutal. We dont have that as you really need the active transmition systems to make it work really eficiently.

The sports cars havent used ALS as much as rally due to the nature of the racing and the size of the turbo's being used. Now sportscars run restrictors the turbo sizes have dropped allowing ALS to work beter.