To go back to the comparison of petrol and diesel Beemers, I don't think it's that much off-topic.
I think the point here is that in 'real life' diesels are heavier and slower than their petrol counterparts but have better economy. Surely the ACO should frame their rules to reflect this natural state rather than trying to show that the diesel is a viable performance engine. So give them the same size tanks, but make them run on pump fuel and reduce their engine capacity, or whatever it takes to make them slower. They could then win by being more economical, which would probably give the manufacturers even better publicity.
Failing that, they should be made to tow caravans!
