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In a message dated 98-09-09 00:27:13 EDT, David writes:

<< 1) at less than 31" it doesnt heat at all in the winter. (well, duh, the
 engine is actually
         sucking air, not producing a higher than ambient pressure which can
be
 bled to
         the cabin--this has somehow escaped the attention of the folks at the
 factory--
         no one at the factory could understand this--apparently they  never
 have to use
         the heater in oregon. >>

If you are expecting the "heater" to work on the ground, forget it. If your
plane is pressurized and the door is sealed and you are at cruse speed, the
engine deck pressure needs to be at least 2 " over cabin pressure. Remember
that the deck pressure is measured before the injector throttle butterfly and
will be higher than the manifold pressure. Also remember that a sealed
pressurized cabin will be about 3/4 PSI above static pressure prior to
reaching pressurization altitude due to ram pressure recovery in the tail
vent.

Under what conditions do you see a drop in manifold pressure? What is the size
of your sonic venturies? The system in my IV-P works great, particularly at
altitude, with no detectable drop in performance.

Sounds like there is something wrong with your installation. I would advise
that you have it examined before you head.

If you are determined to add another heat source, think about an oil-to-air
system in the cabin. In the event of a leak you would only have a little oil
on the floor as opposed to Carbon Monoxide.

Regards
Brent