[Robo.]

Superb post, Camber!

Various combat reports definitely confirm your summary and the version with the holes is certainly correct (opposite to the throttle gate we've got in Clod - that's a late mark thing, e.g. Mk.IX Spitfire with the gate that could be attached both ways in order to restrict or allow the extra movement of the throttle lever regarding to the fuel used etc).

Exact locations of these holes and their diameter are both well researched and documented. Unfortunately, I am far from being an expert and I don't remember where exactly I've seen the diagram with complete cut-outs. But it was certainly not the fuel / air venting (that would be disastrous!) but just the air on the way from the supercharger to the valves, that has been sucked out. I believe these holes have been drilled into original Boost cut-out valves.

I will have a look in the ''Merlin in perspective - the combat years'' publication later on and I will post anything relevant when I come across it.

As you say, the A2A guys seem to have done great deal of research and their FSX product is extremely close to the real thing (although there are some details or say grey areas as with Mk.IIa for example, but fair enough). And the way they portrayed the red gate seems to be spot on. The only problem there is that when you move the red gate, you need to move the throttle back and forth to achieve that extra MFP. This is due to FSX engine limitations and I remember reading that in the real Spitfire, you only moved the gate, there was no extra throttle movement - sort of like pulling the plug in a CLoD Hurricane.

I find it rather unlikely that a Hurricane would use different method od BCC-O than the Spitfire. Everything you wrote in your summary seems to be correct, including drilling the extra holes in order to get safe-sh +12 rather than +16/+17PSI from a Merlin III / XII. This is also quite well docummented including some tests done at Rolls-Royce (BCC-O being backup for failure first and then used as WEP option etc.)

It would be interesting to see if this air suction (with BCC-O activated) had any impact at the mixture richness at all...