Rino,

What you need to find out is the pressure drop across your radiators.
This is quite easily measured.

Then run lengths of the same tubing from the cockpit to the cowling.
Place one open end ahead of and one behind an oil cooler (you can
measure them one at a time, switching tubing locations among radiators
between flights, or plumb everything in advance and then just connect
different tube pairs to the manometer in flight).

Ideally, to protect the open tubing ends in the cowling from stray
dynamic effects you would take short pieces of aluminum tubing that can
be slipped tightly inside the vinyl, squeeze shut the outer ends, and
drill one or two 3/32 or so holes in the aluminum. But this precaution
is probably not necessary. Pointing the open ends of the vinyl across or
downstream should be enough.

You want to record the pressure drop across each radiator at climb
speed. For an aircooled engine you would hope to see a difference of at
least 4 inches of water (the higher water  surface is 4 inches higher
than the lower -- that is, one moved two inches up, the other two down).
I don't know what the corresponding figure is for a radiator, but you
could find out from the manufacturer or perhaps from the Internet.

You certainly have ample inlet area -- way too much, actually -- but
obviously you are not getting the desired performance out of your
radiator(s). Assuming that the coolant plumbing, pump etc is in order,
it has to be a question of air ducting.

Peter Garrison

A small block of porous kitchen foam hot glued to the end  of the tube
also works for stray dynamic effects.

Paul Lamar