Well there is a way
I had my oil cooler remotely mounted on the firewall with tapered plenum for 3" Scat tubing. It didn't work. Even in the winter I had temps well over 200 with climbouts reaching 225. Part of the issue is there is no real direct way to get the SCAT to the cooler.
There are ways to fit the cooler in, while keeping the SCAT duct
short. One way is mount the cooler on the engine mount with adel
clamps and may be an angle or two. No argument, it did not work
for you, but what cooler? You had a tapered plenum not Vans
crummy aluminum box? hummm, interesting. What where the OAT's?
Even a Cessna has OT problems on +100F days.
Everytime you make a turn or bend it takes away efficiency of the incoming air. Simple fluid dynamics.
You are 100% right, bends and length causes loss, but size does matter.
3" SCAT is too small. However from a
Fluid Dynamics standpoint, the
CFM/velocity are low, so duct loss is small, with in reason. You do want
to keep SCAT asap (s=short). They make SCAT with a second smooth
internal layer. Also people aggravate the problem by using the cheap oil
coolers.
I used a standoff box manufactured by Robbie Attaway, to mount the cooler on the baffling behind the number 4 cylinder. I also added two cross braces mounted to the rear baffle and triangulated to points on the engine. Now over 300 hours without problems.
Steve Ashby
Below are pics of ways to mount to cooler off the engine mount (solid)
with a short rectangular duct. This is a direct rip-off of what Mooney
did, as shown: top left and middle left pics. The other pics are two
Rockets, one left one right cooler mounts. You can do something
simular but use a round duct, aka SCAT.
The remote mount sounds good on paper and may work fine in much cooler environments, but it didn't work here.
If you keep the duct work to a min you can use scat, but you need at
least 3.5" or 4" SCAT. If you start with Van's 3" stuff you're at a deficit
already. See pics below:
Bottom right pic shows SCAT going from behind #4 to the cooler,
mounted on aircraft right. That's a little long. There is nothing wrong with
picking up behind #3, which does tend to be hottest, but that is because
the lower baffle chokes the air off to the lower part of the #3 cyl. Proper
baffle gaps allow good cooling so you can pick up air behind #3. There is
more room behind #3 but the battery, if mounted per RV7/8/9 plans, is in
the way a bit. The blue baffled RV (mid left), the air is off of #3 w/ SCAT
to remote cooler. The battery was moved up & over. White cooler plenum
(bottom left) could be longer & more tapered. Smooth inner surfaces of a
fiberglass part is better than SCAT. Also being low and in the corner may
or may not help the exit flow out the cooler? Remote mount coolers work
but short 3.5"-4" SCAT runs & tapered plenums are needed. Note top left
pic has a tapered flange at the baffle as well, which is good. Sharp/square
corners are BAD for flow. This is also why I like mounting coolers with
Adel clamps on the engine mouth to keep SCAT runs asap.
[Note: In pics above, the top right show a wedge shaped plenum; I'd make it
less so with a rounded deeper shape towards the bottom. The RV-4 pic (middle
right) has no plenum at all, just an open plate. This is the RV-4 paradox?
RV-4's tend to cool better than other "wide body" RV's, especially OT. Why
I don't know but its true. He could have mounted the cooler closer to the
engine baffle, still mounting on the engine mount, keeping the SCAT shorter.]