Randy Snarr wrote:
>
> I am looking for some advise on running a plenum on my 235/320 vs. running
> the baffling like the plans show.
>
> How much benefit is there to running a plenum and how much room do I need
> between the plenum and the cowl to allow for engine "shake"?
>
My 235 had a beautiful aluminum plenum when I bought it.  It cooled
adequately but was a pain in the neck.  Had to remove plenum to get at
the top plugs. Had problems with cracks which required re-welding
several times.  Finally learned to leave most of the attach screws
loose, and it stopped cracking.  Also it was a topological problem,
four pieces which had to be wiggled very carefully into position.

You can see a picture of this work of art on the back cover of "Tony
Bingelis on Engines".

When I replaced the 235 with a 320, I went with the standard Lancair
baffling kit.  Putting it on was straight forward, and I built some
internal ramps on the top cowl to smooth the flow.  The oil cooler gets
air separately from a NACA duct on the side.  I've been very happy with
this arrangement and all the temps are good, 350-370 on hot day climb,
320-350 cruise.

Bottom line,  a nice plenum will get lots of oohs and ahhs, but probably
won't cool your engine any better.

Bob Belshe
N19BJ,  450hrs.
Moraga, CA

http://home.attbi.com/~rbelshe/