Posted for <5zq@cox.net>:

 Hello Ron,
 
 We agree with Scott.  We have a O-320 (carbureted), stock except for Lasar
ignition.  Wingtip to wingtip with a few 360 powered planes at low altitude
found us falling behind very slowly, maybe 5 kts or so.  The climb is
definitely better with the 360, all else being equal.  At higher altitudes a
typical 360 will beat us by an even greater margin (balls to the wall, just
going for knots),  But at longer distances we can beat 360's and even IV's
since we'll go nonstop while they will need to stop for fuel (turbines twice).
 
 It all depends on just what you want your airplane to do. When we bought our
engine (factory new) the price difference between an O-320 and a O-360 was
only about 800 bucks as I recall. Fairly insignificant. We chose the 320
because of the type of flying we do. We tend to fly very long legs, often over
water, and really like range, reserve and efficiency. Here, the 320 shines.
It's about 15-20 lbs lighter and can get superb mileage at altitude. For
example, at 14,000 ft we burn under 5 gallons per hour while truing at 164
kts. Here is the record of a recent flight at 14,000 ft:  17.6" MP, 2100 rpm.
TAS 164 kts.
 
 hour 1    6.8 gal  (including takeoff and climb to 14,000)
 hour 2    4.8 gal
 hour 3    4.7 gal
 hour 4    4.6 gal
 hour 5    4.6 gal
 total burn at 5 hrs flight: 25.5 gal.
 
 After 5 hours we had traveled 800 nautical miles and hadn't used half a tank
of gas yet!  That's 32 nautical mpg or 37 statute mpg.  We have 52 gallons
usable. So our suggestion would be to look at your mission. If you just want
to go fast, buy a 360. If you have an interest in range and economy, consider
a 320.
 
 Bill & Sue Harrelson
 N5ZQ 320 1,250 hrs
 N6ZQ  IV  11.88912%