My car is the first Caterham with a factory installed Zetec in the US. The engine is back as far as it can go. My cross weights ae 50 x 50.
The Clam Shells would make the front very light over 110. To a point that I felt more than a little suseptable to cross winds. This photo shows the crude yet very effective splitter/large canard combo now on my nose cone. With it, the car is rock solid at 135+ with plenty of front and rear grip.
One of the Birkins I run with seems to be able to beat me on the long straights. He also has a diffuser with similar HP. Maybe they do help ;-)
Can't upload photo??