This basis for this article
I have gotten form Steve Neophytou.
The reason for Anti-lag is, as it's name suggests, to decrease
or eliminate the lag induced by a turbocharger.
It is mainly used in rally where all Group A or WRC cars are turbocharged.
When you want big power out of a 2 litre engine you need a turbocharger,
and the more power you want the bigger the turbocharger has to be. But
a big turbocharger takes a long time to spin up and create boost pressure
and that's where the ALS (Anti Lag System) comes in. Because
every second a car is off boost a lot of time is lost on a rallystage.
To get rid of the lag the needs to keep spinning at full
speed at all times. This includes when the throttle is closed for
a gearchange, when braking for a turn and when you're a the start
line ready to take off.
To keep the turbo spinning while the throttle is closed you need
exhaust (lots of hot air basically) to keep turning the turbine wheel.
This is how it works:
To get the ALS working you need this:
- P8 ECU - Which the big-turbo Escort Cosworth already have as it was made for rally.
- Pectel anti-lag babyboard - An additional module to the ECU.
- Anti-lag valve - Replaces the original idle speed control valve.
- Modified throttle body - The inlet and outlet ports to idle valve bored out.
- Turbo with 360thrust bearing - So that it will last longer.
- EGT gauge - So you know when your turbo and manifold is going to melt.
- Wiring to "arm" the anti-lag and switch it off - This simply involves wiring
in a switchable earth to one of the ECU pins.
This goes for so-called "mild" anti-lag (see further down for info),
for the real WRC stuff you need
another (very expensive) turbo, exhaust manifold and a few other bits.
With the ALS installed - when you let go of the throttle,
the valve that replaces the standard idle valve in a
modified throttle body opens to let the air continue through. The
amount of air this valve can flow is the only thing that
affects anti-lag, the less the airflow, the less effect the
anti-lag has. Then the ECU retards the ignition timing by 30
degrees so the fuel is ignited when the exhaust valves are open
and most of the fuel is already in the exhaust manifold and turbo. That
makes lots of nice and hot exhaust to spin the turbo and create
boost pressure.
A small "mild" ALS valve can flow enough air to
make 0psi boost pressure at idle/off throttle (rather than -25psi of
vacuum), sometimes up to 7psi of boost, which makes the turbo hit
full boost almost straight away when you press the throttle. The big
WRC anti-lag valve can flow enough air to
produce 22psi at idle (or off throttle), which makes the car have no
lag at all. That will increase the driveability of the car a lot.
Unfortunately the WRC ALS puts a big strain on the turbo and exhaust,
whereas with the 'mild' anti-lag setup is practically as
reliable as not using an ALS at all. It will gradually burn out your
silencer baffles, but all that does is make your exhaust louder.
Some people say that the fuel will cause "borewash" making the need for
a rebuild all the time. But that is not the case. The amount of
fuel used in anti-lag is not enough to cause any significant
bore wash (unless you use £5 budget oil), most
performance cars fuel on overrun, unless they have been mapped for
good emissions, not mapped like that because of reliability
reasons.
Regarding the reliability of Cosworths with the mild ALS installed people
have had it installed for up to three years without any problems at all
even though it has been switched on at most times. The only real
thing you have to be
wary of with anti-lag is that Exhaust Gas Temperatures (EGT) go sky high
but there's no real worry as you could be on the overrun for well
over 30 seconds on 'mild' anti-lag before the EGT will get
dangerously high. If EGT gets too high it could
melt the exhaust and/or turbo. The engine internals will not
have any problems.
For full-on WRC anti-lag the specs is as
with 'mild' anti-lag but with a bigger WRC ALS valve, and a
anti-lag turbo with Maram 247 shaft and turbine wheel with 7° cut-back
blades, Nimonic wastegate spindle and everything nicely put together by a
reputable company at around £1800 total.
You will need that as the extra stop/start shocks and extra heat
would eat a standard shaft in minutes. A stainless
steel exhaust manifold may be handy too as it could stand
more heat than standard one.
For road use you will not need more than 'mild' anti-lag, and for track use it might be
best too as you're on track at sustained periods of time and the WRC anti-lag
may be too severe for those long sessions.
The ALS system won't increase the outright power of your car but it will
significantly increase the power
delivery - much much more low down
torque since the car gets on boost a lot earlier than without
the ALS.
|
|