The lower housing is the stock factory housing

    Lynn E. Hanover

Snip

         Lynn,

      Is it just the angle of the photo or is the factory
housing a 12A? It appears to be narrower. Also it appears
that both housings use no inserts in the exhaust ports.
      Do the exhaust ports show erosion after extended use
in a race car? Would you recommend removing inserts for an
aircraft installation?

          Kelly Troyer

No. The inserts help insulate the housing from much of the heat. Also the 13B exhaust port is larger than the 12A and requires no modification unless racing is in mind. The header pipe ID should be the same or just slightly larger than the ID of the insert at the port face. Large velocity changes (changing diameters) in the exhaust column should be avoided. I changed from 2" ID headers to 1 7/8" headers and the engine came alive in the mid range. Top end stayed the same. Both housings in the picture were 12As. We had a GTP Lola for awhile and the Home grown Periphery port was for that. The car was on national television when at the Mid Ohio GTP race my driver punted the Nimrod (Astin-Martin V-8 powered)off into the weeds at turn 9 when the Nimrod tried to pass on the outside of the turn. My driver never saw the Nimrod. The car was sold with a bridge ported 12A before that last engine went in it, so one partially modified housing is all that is left.
Lynn E. Hanover

I might point out the tuning of a pipe is a secondary function of its diameter.
I suspect the tuning effect of the diameter change may have over powered the increased 
back pressure from the smaller pipe.

Paul Lamar

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/            http://www.linux.org