Question for the Motor Heads

[Blakduk]

Back on topic, a slight reframe of the query:
- throttle steady, maintain altitude (and therefore air pressure is same)
- change pitch to coarse, increasing load on engine, dropping prop & engine RPM
- drop in engine RPM drops RPM of supercharger impeller, decreasing amount of air/fuel forced into inlet manifold
- drop in engine RPM decreases amount of air/fuel being sucked into cylinders.

Question- is the decrease in air/fuel negative pressure at inlet to cylinders more or less than the decrease in the positive pressure of air being forced into the inlet manifold by the supercharger?
If the decrease at the cylinder end of the manifold is more, the boost gauge will read higher as the boost gauge measures increased air pressure in the inlet manifold as there is a backup of air/fuel.

[ARM505]

I'll ask my question another way.

I'm comparing two different models (FSX vs CLOD), both of a Spit MkII with a constant speed propeller:

1) The A2A simulations Spit Mk II running in FSX. In this model, whilst flying at a constant altitude, constant airspeed, constant throttle setting, the indicated boost will DECREASE when you move the prop control lever to DECREASE RPM - the A2A docs mention that since the supercharger is now being driven at a lower RPM, the indicated boost will decrease. The decrease is however very slight.

http://shockwaveproductions.com/

2) The CLOD model, which (under the same conditions), will show an INCREASE in indicated boost when the RPM is commanded to a lower value via the propeller control lever, ie the opposite of the A2A model in FSX.

Since they display the opposite behaviour, one is therefore correct, and the other incorrect. My question is thus which is most true to life. The A2A Spit is widely recognised as a very well modelled aircraft in FSX terms. I have in the past accepted it's behaviour (with the exception of the rapid wear issues) as well modelled. I would like to find out if this is true in this respect.