Look at Van's Blather here.

"Kyle Boatright" wrote:
In talking with Van's, they really thought they would have quite a few
customers for the RV-9 who would use the 0-235 or 0-290. Sure, there
are a few, but there are far more guys bolting on the 0-360 @ 180 hp,
which is 20 hp more than what Van had in mind when he designed the
airplane.

I had contemplated an O-235 powered RV-9A. Here's the chain of reasoning
that I (and probably others inclined to lower horsepower) went through
before realizing it may be a less than optimum choice, even if one seeks to
lower operational expenses like avgas:

When I bought the RV info pack, I finally discovered why the specs on Van's
web site lists the gross weight (GW) range for the RV-9A from 1600 to 1750
pounds: the recommended gross weight increased with horsepower (a
dependency I could not find anywhere on Van's web site). At 118 HP,
recommended GW is 1600 lbs, at 135 HP it is 1675 lbs, and at 160 HP it is
1750 lbs. Now what is the actual structural limit?? Beats me - looks like
the GW goes as the cube root of the HP, so at 200 HP could I safely
increase the maximum GW to 1900 lbs? The designer recommended GW on _none_
of the other RV models changes with HP selection - only the 9 and 9A models
indicate a GW dependent on HP. If the lower max GWs are due to center-of-
gravity (CG) issues, or a takeoff performance issue, then it would be nice
to see that specifically stated somewhere.

Now with an 118 HP O-235 RV-9A @ 1600 lbs GW, Van's typical empty weight is
listed at 1028 lbs, leaving 572 lbs useful, or a miserly 356 lbs useful
with full fuel (36 gallons). So a couple who wish to travel cross-country
and wish to take any baggage at all immediately begins to cut into the fuel
- provided CG issues with that lighter engine up front doesn't limit their
baggage first. Lastly, the install cost difference between a Lycoming O-235
and a Lycoming O-320 does not appear to be terribly great. And if you want
to increase the still air MPG on the larger engine, you can just throttle
back and still get close to the same still air MPG at the same airspeed as
that provided by a smaller engine.

Given all the above, it doesn't seem hard to justify installing something
larger than an O-235 in an RV-9A.