Tuesday, July 10, 2012

Turbo Anti Lag system aka ALS

Anti lag has become a great option for eliminating turbo lag on any turbocharged car in all forms of motorsports. We here at Brewed Motorsports uses ALS in every last one of our  turbocharged engines. Drag racer applications use anti lag to make power when they launch the car, rally cars use another form of anti lag to keep the turbo spooled while lifting off the throttle and now even drift cars are using a “rally style” anti lag option.  Most aftermarket ECU’s as well as factory ECU tuning options are now available with a simple drag style anti lag.

Anti lag systems work by creating heat and pressure in the exhaust system pre turbo. This can be accomplished in few different ways but is most commonly do to air and fuel igniting in the exhaust manifold. The resulting combustion causes the a burst of heat and pressure which in turn rapidly increases the shaft speed of the turbo.

Diagram of the OEM Mitsubishi EVO ALS

Drag style anti lag systems are one of the simplest ALS , mostly commonly used to build boost on the line just before the race begins. By setting up a 2 step rev limiter to hold the desired RPM for launching the car (2 step rev limiter is usually activated by either the clutch switch and or a desired speed)  While a 2 step rev limiter may build a small amount of boost this is not a true anti lag system however it is VERY close. The simplest and one of the most effective drag style anti lag systems is simply a 2 step rev limiter that retards the ignition timing and adjusts the fuel just before it reaches it set rev limit.  This results in the combustion cycle happening while the exhaust valves are open causing a sudden increase in egt’s as well as pressure in the exhaust manifold pre turbo, effectively spinning the turbo much faster and creating the desired boost level. The down side to this is all the extra heat and pressure puts extra stress on everything in its path, (exhaust valves, exhaust manifold, turbo, even the exhaust system post turbo) With proper tuning  the ALS can however be very reliable.

Some testing and tuning of the ALS on the Brewed S13

Rally style ALS are slightly more complicated, there are also a few different techniques used to get the desired results. I will only be touching on the secondary injection style anti lag as this has proven to work VERY well for our Brewed projects as well as 90% of WRC cars (Toyota, Subaru and Mitsubishi just to name a few). By introducing oxygen and fuel (in the proper mixture) directly into the exhaust manifold pre turbo you can produce combustion similar to the drag style ALS without moving the oxygen through the engine (the throttle plate can be closed or at a very low angle such as lifting off the throttle while cornering)  This is the perfect way to lower the amount of stress on the engine/exhaust valves when compared to the drag style ALS as well as provide instant response when reapplying the throttle after lifting. Thanks to the WRC regulations many OEM cars actually came factory with this style of ALS however they were “tuned” off from the factory for the public. Cars such as the Evolution and all all trac celica  could simply re map the ECU or use a standalone EMS and activate the OEM ALS!

WRC engine bay, always a treat!

Good visual and sound of an ALS

Please feel free to ask questions any time! We are happy to give input and advice for any project, of course if you want your car to shoot a bit of fire from time to time and keep that turbo spooled we have covered.