daviddwillson

From what i have read around these forums about the Z bonnets is that the low pressure on the middle of the bonnet and the high pressure air under the bonnet is what causes it. Sort of like an aero plane wing with the pressure on both sides interacting to lift the wing without transport of medium between the bottom and top of the wing. Also from what I've read is that the high pressure at the windscreen acts to STOP air flowing out of the rear of the bonnet. The heater inlet ducts are placed at the base of the windscreen so air is pushed into them, reducing the power required by the pump to suck air in. I'm going to go for a drive today so I'll also put some tape just rearward of the bonnet and try leaving it popped (on the secondary stop) and see if there is any wind flow out of or into the engine bay by doing that.