Its a solid fact and a tool frequently used in the cars of the WRC. Philly's SCCA Rally Cross Chairman and fellow RS25.com member Ryan Schramm (a.k.a. RALLY-FAST) explains all.

" Ever wonder why that rally car goes BANG-BANG after every shift or while coasting? Becasue it's equipped with an Anti-Lag System, or ALS for short (some people also call it the bang-bang system but from here on out I'll refer to it as ALS).

 ALS is an engine management system that minimizes turbo lag by injecting fuel and air into the exhaust stroke of an engine. The air/fuel travel down the exhaust where it meets the hot turbo vanes and BANG, it burns (expands) rapidly and keeps the turbo spinning to produce full boost while the driver releases the gas pedal.

First a little history:

 ALS really was born during Audi's dominance of the group B rally era of the 1980's. Group B cars were fitted with HUGE turbochargers to compress large amounts of air to make huge power, which because of their volume had significant amounts of lag when the car was not at full throttle. Stig Blomquist and Walter Rohrl (There is debate as to who was first, so I give them both credit here) realized that there was no lag if you never lifted the throttle. So they just kept thier right foot down while pumping the clutch and using the left foot for braking duties. Since this was hard to implement and even harder on the transmissions, they were quick to learn that a new system was needed. The first ALS system was fairly crude- an additional injector to add fuel directly to the exhaust before the turbocharger. This resulted in keeping the turbo spinning fast and happily producing full boost. However there often wasn't enough oxygen to allow this extra fuel to burn up before exiting the turbine housing, resulting in spectacular (and quite dangerous) flames shooting from the tailpipe. Eventually the Group B cars were outlawed becuase they were too fast, which subsequently resulted in the introduction of the WRC class in the late 1990's.

Today's ALS Systems:

 When creating the new WRC class, FIA implemented a new rule of using a restrictor before the turbo to limit the volume of air the turbo can compress, essentially limiting the power output. This was to keep the cars competitive with one another and to help control speeds on the stages. (today's WRC cars often set new records much faster than that of the legendary Group B cars). A new system was needed to help the car accelerate and produce power at lower RPM's. Toyota was the first to implement this new design, follwed by the Ford Escort Cosworth, Prodrive/Subaru, Mistubishi and others.

How it works:

 A standalone engine computer system retards the ignition timing (often 20-40 degrees of delay (depending on whether your car has 3 or 5 stars on the badge), and the fuel/air ratio is increased as the driver lifts the throttle. With no spark during the power stroke, the exhaust valve opens while the spark is introduced and the unspent feul and air travels down the downpipe towards the turbo. When it reaches the hot turbo vanes, the engine management tells the spark plug to fire, and the fuel burns rapidly which keeps the turbo spinning. The response if full boost pressure at vastly lower RPM's. Most systems have user selectable maps for more or less agressive conditions and terrain and usually can be turned off for road (transit) sections of rallies.

-Vastly increased temprature of the exhaust and turbo. Exccess heat often degrades the turbo's oil seals much faster than a normal car, as well as cracks in the metal of the exhasut become more common with the increased temprature. A common myth is that the trubo needs replaced every few hundred miles. the fact is that with today's technology such as ceramic turbo vanes, better welding techniques and high quality componenets, turbos' can last much longer. Keep in mind that there are many variables and things can and will go wrong.

Further Reading:

Also check out these books and magazines:
Race and Rally Car Sourcebook, by Allan Staniforth
Perfomance Ignition Systems, by Christopher Jacobs, PhD."

Special thanks to Ryan Schramm. Be sure to check out his work at www.Brokenmotors.com

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