ALS and 2-step are two different systems. Here's how I understand them both.
A 2-step rev limiter creates a second ignition cut point with no fuel control at all. It is usually used to spool a turbo on a manual transmission car for drag racing so you can launch with boost. Typically wired into the clutch switch so it only acts when the clutch is fully pressed. It makes noise and pops flames out the tailpipe, but doesn't adversely affect the turbo as badly as ALS does. The pops/flames are created by the exhaust system getting saturated with air-fuel mix coming out of the cylinders when the ignition is being cut off, then it being ignited when the ignition kicks back in.
Anti-lag (ALS) is a performance setup that is used in rally racing a lot, due to it's ability to keep the turbo spooled at all times. It works differently by retarding ignition timing and adding extra fuel to the engine during shifts and coasting. What that does is basically makes the engine into a jet-engine by throwing flames out of the cylinder when it's still burning. That lets the gas expand in the exhaust manifold, thus adding energy to the turbocharger, keeping it spooled for when you get back on the throttle. This is dangerous to the turbo because that fire coming out of the engine is very hot, and only gets hotter as it burns. That makes exhaust temps skyrocket, which can damage the exhaust housing or the turbine wheel is used too much or if it's set up incorrectly. Good for a single race, but if you want to re-use the turbo, not such a good idea.
In both systems the wastegate functions as normal by controlling the exhaust flow bypassing around the turbine. I'm sure both have been used with a CT26, but I've only ever used a 2-step with mine. I could hear the turbo spin up, even at 2000rpm in neutral, it's very cool. I have heard of turbos being very severely damaged or destroyed by misuse of ALS settings...
If anyone sees anything way off, please correct me!
