Exactly !

Surely its about the air speed and keeping things equal.

For those that that haven't seen it have a look at MK's Fiesta thread and the photos and write up of the current Fiesta WRC, I'll go with the fact that if Msport have tested everything and come to the conclusion that a small tb works perfectly then there is no need for a larger one than the Yb comes with.

IIRC they use something around the same size as a stock Cosworth one.

Very interesting pictures and info for those that haven't seen it.