Has anyone tried running their Le Mans bonnet with vents cut into the two dips on the top? I'm sure I heard something a while ago about it upsetting the aero, but I can't think of how it would have a big impact unless it made the bonnet blow off with pressure differences.

It seems like it would be good for getting rid of hot air above the exhaust.

I wondered about bonnet vents as well, though was thinking of vents further back, sort of Aston Martin style. I'm sure I've seen some of vents you describe on the early Furys and you see a lot with vents in the side of the bonnet.

In terms of impact on aero, I don't know that answer to your question, but would have thought vents would lower the air pressure under the bonnet and reduce front-end lift.

Try sticking bits of wool on the area with tape, see what is going on. Airflow can do very unexpected things especially where shapes change.
I know on my car here is a high pressure are just in front of the screen, so vents there do nothing. In fact it is where the intake is for the interior ventilation/heater, and at speed air flows under some pressure. The implication is that a hole in the bonnet in that area would increase under bonnet pressure, and also increase front end lift....

Things are not what they seem and certainly not simple

I trimmed out the vertical face of the "dips". Hot air definitely exits through them as you can be seen by the behavior of water droplets there in the rain. I also have 2 small side vents.

The area indirectly in front of the screen is a high pressure area and people with the classic (big bulge) bonnet have cut out the rear of the bulge and then seen water being sucked IN. On the flat top area of the LeMans bonnet there's an area of still air; Even at motorway speeds water droplets just sit there.

Gratuitous pictures of the vents doing there stuff in nice locations (sorry only shots I have of them)...

Climbing the Lauteret...


Surviving an hour in +90c temps in Genova rush hour...

Also cut mine out on my old Fury.

Used the front rounds to give a better feed to the air intake. Worked well for me but may not be the best method.

Thanks, that answers some questions. It seemed a bit odd that the bonnet had been designed like that and I hadn't heard much about people opening them up. I guess there would be a bit of a venturi effect so air would be sucked out of the engine bay at speed.

Something to look into when I eventually get the car back on the road.