If you've watched any rallying for a minute or two, you've heard ALS at work even if you had no idea. ALS in very basic terms is a method to keep the turbocharger spinning and producing boost even off-throttle. So what? So what?! You're not reading this blog if you don't like boost (and as we all know, boost is better kekeke!), so ALS is like Beethoven's Ninth to us turbologists!
ALS is critical in racing because it maintains constant turbo boost during all throttle conditions. Since most lesser-displacement 4-cylinder engines rely on turbochargers to level the playing field versus good ol' displacement, it's crucial that those turbos function efficiently to close the gap. Sounds great, who cares. Maybe you're at the wrong site...
Turbochargers are modern (well that's debatable) marvels of engineering. They are powered by spent exhaust gas at no parasitic loss to the engine and create immense horsepower and torque. However, just like any rotating mass, they require force (exhaust gases) to overcome inertia. The time this takes to happen is known as turbo lag.
Turbo lag is in simplest terms the time it takes the turbo to produce the desired boost level. In the earliest days before ball-bearing center cartridges and variable geometry turbos (aka VNT), turbo lag on brutal cars like the Porsche 930 often led to hairy driving conditions for all but the most skilled drivers. Plant the gas and pray.
So, one could make the argument that ALS, in its effort to eliminate lag, also provides for a more predictable, stable car under cornering, as the power is already in place with no sledgehammer effect. More basically, ALS serves to greatly expand the usable powerband of WRC cars, which is very important in exiting turns with minimal traction.
OK, hopefully that sheds a little light on the subject without diving into the deep end technically (which we will do a bit later). Let's observe ALS in its natural environment, shall we?
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