This something I wrote a long time ago when I was in the engine business. Thought you might find it interesting reading.
Good Luck,
Mahlon
I am a engine guy not a RV 9 guy, so you have to bear with me if I am
missing something here, but I can't see any disadvantage to using a O-
360 on a 9 other than approximately 14 pounds loss of useful load.
First off any engine using a fixed pitch prop never sees rated
horsepower during normal operation. An O-360 is rated at 180 Hp at
sea level at full throttle and 2700 RPM. The only way you will get to
those numbers, with a properly pitched propeller, is at full
throttle, at full speed, at sea level. The engine will most likely
never see more than 2500RPM during climb or at takeoff power, unless
you climb the aircraft very flat with a climb prop on it. The 180HP O-
360 is alternately rated at 160 HP at 2400 rpm, so a 180 HP 360 with
a cruise prop on it, will likely only turn 2400 RPM during take off
and climb at sea level. Guess what, a true 160HP from the 360 just
like the fixed pitch guys get with the constant speed equipped 320
(160HP + 2700RPM and full throttle). All you have done by turning
2400 is de-rated the engine to 160 HP! Now if the climb is flat or
the speed builds up, pull the throttle back and keep it below 2400
RPM for a true 160 HP. Imagine what this will do at altitude, you
have a cruise prop installed and 20 extra horsepower at your disposal
to use, as you climb to higher altitude. Wow! This is a great way to
go for those operating out of higher altitude fields all the time or
just fly high all the time.
Some say, it is too tempting and you will break the 160 HP rule or
you do most of your flying at low altitude and you don't want to have
to manage the throttle so much, so lets have some insurance. We put
low compression pistons in the 360 and you now have a 167 HP, O-360.
rated 2700 RPM. Guess what! With climb prop we now get 2500 RPM
during sea level take off and climb..... That's right, a true 160HP
at 2500 RPM. And to boot you still have the extra 7 horsepower at
your disposal as you go up.
The key to all this is you have to regulate engine power with the
throttle. This is done everyday, all the time, with a fixed pitch
prop and engine combination.
If you have a slightly under pitched prop (or as some would call a
super climb prop) on a 320 like Clay seems to have, you have to pull
the throttle back to prevent exceeding RPM limitations and thus true
horsepower output. No different with the 360 with fixed pitch prop at
180 hp or 167 HP.
The 2400 RPM 160HP 360 is a certified, Lycoming engine, not something
I am making up..IO-360-L2A used on the more modern C172 RG's is a 160
HP 2400 RPM 360.. fuel injected no less! So is the O-360 J2A. The 167
HP O-360 is a certified engine as well; it's the O-360 D series of
engines.
You can use the same logic with a constant speed prop, use a prop and
gov limited to 2400RPM at take off, like the 172RG, and get a true
160HP at 2400 and full mp just like the 320 constant speed guys at
2700 RPM..The down side is no more oomph at altitude. Same with the
167 HP versions, prop gov set to 2500 RPM and you have a 160 hp
engine, again with no extra power at altitude.
To me the fixed pitch version of this scenario is the way to go with
very little throttle management (no more than an under pitched 320)
you get a full 160 HP with plenty of power to keep things going well
at altitude. The 360 engine is less expensive if you are purchasing a
non vans supplied one, and so is the fixed pitch prop but the
performance is the same as the more expensive 320 with a constant
speed prop!
I know you have to think "Out of the bun" here, because nobody told
you about this before and the support from Vans using an O-360 isn't
really there. But other than about 14 pounds (heavier) fixed pitch to
fixed pitch,( one muest understand that the fixed pitch 360 has a solid flange crankshaft that weighs more, If you compare the weights iof the hollow shaft 360which is the cinsatnt speed version and the hollow shaft 320 constant speed version the weight difference is only o or a little taller (about 2 inches) and a little wider (1
inch) and the carb air box mounting flange being a different size the
rest of the engine is the same as a 320 on the outside. From what I
am told, the 360 will fit on the airplane with the -7 360 cowl and
you get the performance of a constant speed 320 for a lot less money
with about the same weight up front, if you consider the weight
difference of the cs prop on the 320 and FP on the 360. Even fixed
pith to fixed pitch the weight difference is 15 lbs total prop and
engine to prop and engine.
I hope the operators of lots of the 360 powered RV9's reply to Clay's
post, as I can't see what is undesirable with the 360... but I would
sure like to find out if there is a down side.
Please shoot holes in this explanation, if I am wrong or if I am
missing something, you won't hurt my feelings and I will learn
something!!
Good Luck,
Mahlon
These are actual weights of the engine as shipped from us.
The superior O-360 weighs more then the O-360 listed due to the fact the sump weighs more then the one Eci or Lycoming uses. Superior lists the weight of there O-360 with a hollow shaft as 287 lbs which is 6 lbs heavier then the same exact engine with a Lycoming or Eci vertical sump installed.
TMX O-360 Fixed Pitch (Solid Shaft 180HP):
25"x 33"x 29" 286 Lbs.
TMX O-360 Constant Speed (180 HP) :
25"x 33"x 29" 281 Lbs.
TMX O-320 Constant Speed (150/160 HP) :
22"x 32.2"x 29" 274 Lbs.
