Antilag? Go to the source.....
The Umluft
Audi made a very ingenious and effective antilag system for their quattros on the groupB era.
Effectively they ran 2 sets of wastgates on their exhaust manifold. One was a standard wastegate controlling boost pressure by bleeding exhaust gasses. The other wastegate was acting as a relocated bypass valve directing boosted air that would have normally have to be bled off to the atmosphere back into the exhaust manifold.
Add a second set of injectors(or a layered injection pattern) to take advantage of the extra air being injected in the exhaust manifold...presto, antilag.
They do say though that this was on the extreme side of things in the antilag genre requiring frequent rebuilds(exhaust valves only last for 1hr?...yikes!). But its interesting as a look at how it was done.
Gavin