I am on a mission to reduce under bonnet temps and I have looked through every post on here I can find. Most people seem to cut holes and hope for the best but aerodynamics are a slippery beast and you might make things worse.

Westfield do a V8 nosecone and can anyone explain how this works? Apparently the lip in front of the vent changes air pressure and helps draw air out. Can anyone explain????

That's a ducted nose - the coolant rad is fixed to the nose cone and the hot air is ducted out of that hole and not into the engine bay.

As above,any air that passes through the rad goes out of that top hole rather than into bay.

Looks a good idea,do they work?

If you haven't already seen it, scutter has a good solution here :-
http://www.locostbuilders.co.uk/forum/4/viewthread.php?tid=188555#pid1586573

I think really what you asking is how does a lip in front of a vent help?

Well as the air hits the lip, it is directed upwards and thus making a lower pressure area behind and therefor pull air out from the vent