To accurately test the effectiveness of a ram air system put a selector
valve on the pitot port of your airspeed indicator allowing you to switch
between pitot pressure and manifold pressure. Compare the two indicated
speeds. If there is no change you have a great ram air system.

Bill,

 

Not so.  However, one might construct a pitot tube and switch it into your MAP sensor.

 

1. Engine ram pressure includes air that is being drawn off occasionally depending on valve and piston position.  A closed pitot air speed system is closed. 

 

2. MAP is an absolute measure - not relative to ambient as measured thru a static air port.

 

3. The theoretical max ram air pressure from attained air speed can be calculated - i.e.

 

KIAS  "Hg (approximate)

 248   3"       (Legacy)

 200   2"       (Lancair 360)

 175   1.5"    (Lancair 320)

 150   1"       (Cozy 360)

 125   .75"    (Liberty)

 

Thus, if your airplane is slow (<125 KIAS), you will see less benefit from ram air and even less if you ignore .4" Hg because of where the air comes from.

 

Of course, you must be operating WOT to reap the benefit of the wings flying at the less draggy altitude whilst your engine believes it is several thousand feet lower..