depends on the class of cars we are talking about, for the 6 cylinder class it would have to be the XR6 Turbo with a 4lt straight six would have to be a high contender, Holdens 3.6lt V6 engine does not come with a turbo, unless you buy an after market one.

the V8 class would have to be a Holden 5.0lt 308. Aussie made motor that in it's day was the best you could get. i think the last model with that motor was a VR, after that they started to import from the US.