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In order to understand the cabin heat system in a LIV you need understand
what is going on in the engine.

Ambient air passes through the air cleaner and then the compressor section
of the turbocharger. The pressure between the discharge of the turbo and the
inlet of the throttle is referred to the Deck Pressure. The pressure between
the throttle butterfly and the intake valve is the Manifold Pressure.

The sonic venturies are connected to the Deck Pressure. The turbocharger
controller and waste gate maintain the deck pressure above the manifold
pressure by several inches. Manifold pressure is set by the pilot. Under
most conditions of flight, the deck pressure is above the ambient pressure
regardless of the manifold pressure. The deck pressure cannot fall
significantly below the ambient pressure so the sonic venturies cannot
"suck".

An excellent reference is the "Aircraft Turbocharger and Control Reference
with Troubleshooting Guide" published by Garrett / Allied Signal
(Publication # TP25-0111-3).

Regards
Brent Regan

LML website:   http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore:   http://www.buildersbooks.com/lancair

Please send your photos and drawings to marvkaye@olsusa.com.