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Here's another tidbit from the
New Braunfels fly-in that I forgot to include in my earlier
posting:
Tim Ong passed along a recent
experience with the ram air in a Legacy (can't remember whose). They had
the ram air pulled (on) at altitude, and started to pull the mixture back toward
the right (lean) side of the hump. When they got there, the engine
abruptly quit! Apparently this was reproducible, and led to considerable
head-scratching in their debrief.
The conclusion is that when
manifold pressure starts to exceed the ambient pressure, i.e., the pressure in
the cooling plenum, the venturi effect that provides atomization of the fuel
charge in the injector nozzles quits. When the pressure gets "upside
down," air is no longer drawn into the fuel charge, and this is apparently
rather upsetting to the engine, which displays its pique (sorry, bad pun) by
going very quiet.
This is similar to the situation
in the TSIO-xxx, and the fix will be the same, also. That is, a different
shroud is used over the injectors, and air, instead of being pulled in from the
ambient air, is ducted to each injector shroud from the intake manifold.
One could either add the shrouds and rails from the TSIO parts catalog, or build
up something similar. My A&P tells me that the injector bodies on my
IO550 are the same as what's on the TSIO-550. There is a second O-ring on
the injector body, not installed in the normally aspirated engine, that will be
needed for the new setup.
Tim said he was thinking about
putting together a retrofit kit, but wasn't sure when it would happen, as he's
leaving town shortly for some weeks. Meanwhile, it looks as if the choices
are either ROP + ram air, or LOP and no ram air.
It would be interesting to know
if any others are flying Legacy's with the ram air added, and what happens when
LOP operation is attempted.
Jim Cameron
Legacy N121J
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