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Jim commented on the last list: "Although there is no
alternate air with this setup, if you get both of these large filters iced
up, alternate air isn't going to help you -- you need a parachute."

Parachute indeed. There is another icing effect that is unique to filters
and not generally discussed. Ice crystal clogging. This occurs when you fly
through stratus clouds in the flight levels. The ice crystals, which don't
stick to the airframe, are caught in the filter, like dust, and clog it. If
the accretion rate is greater than the sublimation rate then your manifold
pressure will drop precipitously. If you don't have an alternate air door
then you will need "lower".

Be advised that drawing alternate air in the flight levels will cause a MP
drop due to the higher density altitude of the hot air coming off of the
engine. This drop will be less than that caused by a clogged filter.

I am also thinking (although I have never witnessed this effect) that in a
starved intake situation the turbo controller will be insisting on
maintaining high MPs, causing the turbo to run at higher and higher pressure
ratios, all the while the air mass flow is dropping. Can a compressor stall
and flameout be far behind?

I can say that a flameout at altitude is one most exciting events that you
can have and live to tell of it. 8~O

Alternate air doors, get them or wish you had.

Regards
Brent Regan

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