And I too "should be seeing about +1.5" Hg added to the MAP because of a dedicated ram induction port" but I clearly am not.  My ram air port now adds only .25 to .35 inches of pressure and I don't understand why not more.  Clearly, the consensus of our builders and fliers favors the installation and use of ram air ports in our Lancairs. 

 

As I understand it, the worst that should happen after I remove the ram air is that my aircraft performance should be no worse than it now is - and that is a happy event!  Like you, I am capable of flying at 183 knots using just 90% of my available power (long wings, 0360, after-market injection and electronic ignition).  More often, cross country flights are at 12000 feet and 175 knots cruise.  I love it!

 

Removing the ram air should reduce weight and complexity while facilitating maintenance (cowling easier to remove & install), streamlining the cowling and permitting better sealing of cooling air.  The experiences of others have varied but, for me, the only downside that I can see is a theoretical reduction in speed/power at high altitudes and airspeeds (but not on takeoffs, landings and slower airspeeds).  Are there other safety or performance factors that should be considered?

Greg,

 

Please note that the way you measure MAP improvement can be misleading.  Sensitive altimeters are calibrated to respond to air pressure in certain ways that do not match the absolute pressure instruments sensing MAP.   Care to calculate air density given the temp and water content?  Altimeters do no necessarily yield the absolute altitude - they are TSO'd to make sure the other guy is reading the same altitude that you see indicated (within some small error).  It works better that way when you are approaching each other and should be at least 500 feet apart (one IFR, one VFR) regardless of the absolute altitude.  Thus, any "ambient pressure" calculation using an altimeter is bound to contain error.

 

The MAP sensor only cares about the absolute pressure it sees from 1/4th or 1/6th of the induction system, smoothing the reading between clanking of the various intake valves, prop induced air flow disturbances, etc.  If one would obtain a second absolute pressure sensor and expose it to the ambient pressure...... Of course, then we would have to fly with and without ram air to see what the difference is.  Those with alternate air could report the difference in cruise by manipulating the gate.  Which leads to the second confounding issue....

 

Not all ram air setups are equal.  The leading edge of the ram intake must not be sharp but rather blunt and outside the boundary layer.  The intake diameter can start out somewhat larger than the final induction diameter so that the air can be accelerated and the pressure recovered when the system expands (like into the cylinder).  There are other schemes (See Fred Moreno's beautiful set up).  The ram intake walls should be smooth so as not to confound the air flow (another words, SCAT tubing is not an ideal connector).  Some have used a high quality air filter with only small losses across the media whilst others use no filter on the ram system.  Those that have an alternate air source may be messing up the air flow inside the ram system even though the door is closed.

 

While I have used my airplane in practical ways (cross country weather flying), the main purpose is to flog the 320 so that it beats most 360s - it is the little engine that could.  Believe me, I am not pushing my 320 engine to reach 183 KIAS.  Now, flying at 2000 MSL, WOT, 30.2" MAP, 2700+ RPM for two hours from Dayton to Fond Du Lac at 202+ knots measured for the course (2006 Air Venture Cup), that's something different. 

 

There are no special safety or performance considerations should you rid yourself of your ram air system.  Your engine will perform just as was expected by the manufacturer.