Spit Mk1 Boost?

[Robo.]

Originally Posted by Crumpp

The maximum boost is only +12lbs at sea level in emergency override in the Spitfire Mk I.

That is all the Merlin II and III were capable of handling and that was a definite over boosting of the engine.

Yes, Sir, you're kind of correct - +12PSI is the rated boost for a Merlin III with the plug pulled. +17PSI was never a rated boost for this engine, but the engine was actually capable of it.

In fact, the BCC-O was still limiting the 'natural' boost DOWN TO +12PSI by drilling a 3mil hole in there. It is also known fact that some pilots during Battle of France liked to put a matchstick into that hole getting +16PSI effectively on Waybridge prop Hurricanes, beating the hell out of the poor thing. No, I don't want that modelled, I just mentioned it because I find it interesting.

Noone ever said the Spitfires were flying at +17PSI, even the +12PSI was restricted. The reason he mentioned it was TomcatVIP's post regarding overboosting I believe.