[Dalton]

Lance, your build is innovative and interesting, and it is enjoyable to follow a builder rethinking the approaches to areas without merely replicating the original. For a road car that is intended to be used frequently, you are doing all the right things to keep it drivable and user-friendly, which is a different approach to either the super accurate replica, or the competitive racing sports car.

I have a thing about air conditioning, and always like to get car air systems working well. Most GT40 replicas with air conditioning seem to merely recirculate cold air. The fresh outside air has to be introduced separately. This may be via an aviation type air scoop in the side window (I forget the proper name; old age). It has been interesting to read of some builders on the forum taking outside air from a front clip intake and ducting it to a plenum on the air conditioning intake, via a manual volume damper. If you run part or all outside air, through the air conditioning supply fan, you get a good positive pressure from the ram effect (moving at speed) plus fan, which easily expels old air from the cabin.

Looking at your proposed relief arrangement, while your concept is a good one, I think you should definitely check the pressure at the mirror housing with a manometer first as you suggest. Then I suspect you will need larger ducting or the friction and small cross section area of the ducting will reduce air flow to a level not worth bothering about. With the bulkhead right behind the seats, if you don't want a roof vent there aren't many options. Could you vent through a slot in the bottom or trailing edge of the door, outside the location of the rubber sealing strip? Any noise issues could be addressed with acoustic insulation in the door around the slot to provide attenuation. Just a thought.

Dalton