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You asked for comments, so here they are:

 

First of all, every engine can be made to perform across a range of HP, given that the displacement stays the same.  The parameters are based on the compression ratio, ignition system, fuel delivery system and the air induction system.  Performance (HP) can be enhanced by opting for a higher compression ratio, electronic ignition, fuel injection, utilization of ram air for MAP increases and other adjustments to ensure that each cylinder is delivering the same HP as the others.  Fuel use will vary commensurate with HP delivered.

If you choose to utilize all of the above, fly high in the best altitude range as intended by the designer (320/360 = 8000 to 10000 MSL), operating the engine LOP and at an appropriate power setting you will have achieved engine optimization/economy.  Further efficiency can be gained by making sure that drag components are at a minimum - these may include minimizing cooling drag, using control surface gap seals and keeping weight down.  Using a prop designed for the speeds you will fly, whether constant speed or fixed pitch, also contributes to efficient flight. 

 

However, always remember that increased cubic inches can result in quicker climbs and more power available at higher altitudes, all other things being equal.  One can always reduce the throttle setting.

 

I happen to like my Lyc IO 320 and I do utilize all of the items I mentioned earlier.  Let's see, the other day I flew a 100 NM trip to visit a friend.  Outbound at 6500 MSL,  2500 rpm, WOT and ROP, I made the trip at 10.4 gph and an KIAS of 181.  He challenged me to return home more efficiently and so I did.  Returning at 5500 MSL, 2400 RPM, 24 MAP and 50F LOP, I was using 7.2 gph and about 174 KIAS - boring.

 

My friend has a very nice "blueprinted" Lycon 360 and when we operate in formation and ROP, his power parameters are about the same as mine and so is his fuel consumption (we have the same type of engine monitors and fuel flow measuring devices).  He uses P-Mags and I use the Light Speed Engineering EI. He uses a 2 blade MT CS prop and I use a Hartzell CS prop.

 

Now, go out there and make that engine the best it can be....

 

 

I opted for the 360 in this plane, but sometimes think I may have made a mistake for what I plan to use the plane for.  I plan to make many cross country flights.  I was looking for economy and I am sure I will get it with the  360, however I do not know if a 320 would have made more sense.  In the upgrade I had to get the extended mount, which in turn led to extending the cowling, moving the CG etc.

 

If  the surfaces are straight, true and clean, then the 320 will cruise at just a little less than the 360 on a lot less fuel, if what I read is correct.  Sometimes I wonder if I needed to do the KISS thing and just go with a 320 and the basics, and put the money into optimizing the basics.  Any comments