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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