put a small turbo in the 220 ST mondeo (or in a 2.0 mondeo - petrol engine).
easily smash the diesel version.
petrol have a better thermal efficiency.
i don't remember the exact percentage but i think is double of the thermal efficiency of a diesel engine.
the only good thing of a diesel engine is the consumption...lower diesel quantity for the same mileage...and the diesel is a little bit cheaper (in italy about 1,10 euro - petrol is 1,35 euro)...
but for sporty cars,diesel is not the better choice...
(audi R10 diesel is helped by the LMP's championship rules)