The VAG unit. V10, forty valve motor with two pairs or turbochargers.
I think the problem would be fitting it into the middle/back of the car. Also, its sheer mass (weight) would upset the handling.
Alternatively, how about the 2.7 litre PSA/Ford V6 twin turbo. Might just about be able to jam it in.
I'm being silly here, taking the p... out of my own posts. In a raw two seater with no luggage space it's got to be a petrol engine that revs to 9000 rpm. Diesels do everything else beautifully in big sporty saloons but not in lightweight racers.