Heater bonnet vents

The final step of the heater move, inlets on the bonnet;

My layout has a central pattern to line up with the heater inlet, and two side patterns which are both for aesthetic reasons and to let more engine bay heat out. They will let rain water in but the amount this car drives in the rain - I'm not concerned about it; any ingress will drain directly through over the gearbox to the road.

The layout is 10mm diameter holes, 10mm apart left/right, 15mm apart fore/aft laid out in powerpoint and printed to scale. Template aligned with the heater inlet underneath. Prior to starting I tested hole spacing on a scrap to ensure it didn't weaken the area too much:

3.2mm pilot hole widened to the 6mm required for my sheet metal punch. I carefully drilled them with the bonnet in place on the car - it was the easiest way to hold everything rigid, just needed some care with length of drill bit and awareness of what was underneath:

The sheet metal punch leaves a completely finished hole, no need for filing and a very slight bevel towards the inside of the bonnet:

31 holes, 2 hours work - result as planned though, pretty happy with that:

I just need an opportunity for a drive to see if the heater can still pull in air from the boundary layer around the car when it is moving.

Thats it - the end of the radio/heater project!

Update - short trip round the block today, there is certainly a draw of air through the heater, without the fan going, just using the cars forward speed. The area I have my inlet vents must still be close enough to the windscreen to be in the high pressure area.