I did not read the whole thread but....
FREE FLOWING in-take, induction from outside are to intake valve and non restrictive exhaust from exhaust valve to outside is "GOODNESS" (technical term requiring years of engineering school). It will make more HP and
better efficiency because the engine does not have the WORK HARD to SUCK and BLOW... as in Suck , Squeeze , Bang , Blow.... 4 Cycles of your Lycoming and all Otto cycle engines. Why do people put on turbochargers and super chargers on airplanes? To increase MAP and fly higher where drag is lower. YES INDUCTION RAM AIR IS GOOD.... always at any power from 100% to 50% and lower. You control your MPG in an airplane with that black knob thing (and the RED and Blue if you have it). In a car it is the skinny pedal.
So what does that mean? You will make more power and have better efficiency. Those are good things you want always. Efficiency means lower fuel burn for given HP. The design of the Van FAB not only does a good job of recovering RAM (the dynamic pressure from doing say 190 MPH) it also has lower airframe drag, especially compared to a typical Cessna.
Van's standard up draft FAB airbox into a Carb or Throttle Body is good for about 0.5 inch (guessing could be better, as much as 1"). It is SO hard to measure this RAM (dynamic pressure over ambient). How I have done it is pull CARB HEAT and block RAM air.
I get 1 INCH drop, or one could assume RAM air is good for 1" RAM. Some of the loss is Engine sucking warmer air inside the cowl. Some of that is restriction in the area of carb heat opening, which is smaller than the main inlet.
But most of the loss or lower MAP is loss of RAM AIR... I am guessing 0.5" to 1.0 In-Hg. THAT IS FREE BOOST. This is amazing because most planes LOSE MAP due to very restrictive induction system and airbox.
Keep in mind the TOTAL RAM avaiable at 8000 ft at 190 mph is 1.0 Inch/Hg... So it is not realistic to think we gain a full 1" if MAP but we come close. On slower planes there is less RAM to recover.
What about CESSNA with an AIR FLILTER plastered FLAT on the nose bowl of the cowl? Looks OK? Nope. If you do the same flight test I did above on my RV in a Cessna, you will see small loss of MAP with carb heat. (Anyone have a number of MAP with and w/o carb heat in a Cessna). The Cessna air-filter/airbox is already operating with restrictions and nil RAM recovery. It is terrible and even w/o carb heat you have no RAM air induction gain and even lose MAP.... Also a Cessna is much slower (less RAM) and their carb heat is a flame thrower and VERY hot less dense air, so it is hard to draw a straight line between an RV and Cessna. Bottom line aerodynamically the Cessna air filter is draggy and recovers little to no RAM. Van's FAB does better than any Certified Aircraft in the induction/filter/airbox design and performance (in my opinion).
I also estimate Van's airbox efficiency by looking at Lycoming's WOT MAP for a given altitude adjusted for Temp/Pressure and other (certified) Aircraft AFM'a. My RV MAP is higher than what Lyc predicts. Also looking at other aircraft manufactures AFM (say a 180/200HP Mooney), comparing their MAP at altitude charts to mine, my RV has better MAP (and is faster). Later model Mooney's have true RAM with NO AIR FILTER used only in altitude cruise and selectable by pilot from filtered to no filter RAM. Sporty and pilots who leave RAM on in snow and ice have had the engine shut down due to blockage of induction. It is to be used in clear air in cruise. However this system does produce induction RAM recovery and better performance. Does Van's FAB having air filter you can not bypass reduce RAM induction? Yes slightly but the K&N is free flowing and the air velocity has slowed to recover pressure. The FILTER can improve performance, has benefit of smoothing out the airflow into to the induction (Carb or Throttle Body).
Lyc has a hot oil sump the induction feeds through. This makes CARB ICE less likely but warmer air, the less dense air causes loss of HP. Continental's with carbs are more susceptible to Carb ice issues with cold induction (induction is separate from sump with hot oil).
FI you can get a COLD INDUCTION sump on Lycoming. Colder air is more dense and makes more HP. Just keep in mind ICE/Snow can get into the induction system of FI (fuel injected) planes. If you love flying in clouds, snow, freezing rain) your FI Lycoming needs ALTERNATE air input (not carb heat but just another source of clean warmish air if the air lifter gets blocked by ice/snow)..
Exhaust? Another story. It is not induction but it is the flip side of induction. The IN has to work with the OUT. The exhaust on certified planes are heinously bad. That is why companies like POWER FLOW look like hero's putting their tuned exhaust on GA planes. They get lots of extra HP and thus better performance. Part of the dramatic increase in HP is not because they are quantum leap or new technology (it is tuned exhaust well known). It is the contrast to stock exhaust which is very bad.
No kidding MORE HP is always good... as Tim "Tool Time" Taylor would say, "more power".... Get all the RAM induction boost you can get regardless of the power setting. It is SCICENCE.