<< Lynn,
 >
 >   What size tubing did you use for intake runners on this PP engine? I've
 > heard numbers anywhere from 1.5" - 2.25" diameter. The Powersport guys I
 > think are using 1.5". My guess is that idle quality improves with the
 > smaller tubing by keeping the velocity up. Trade off would be less peak
 > power at the higher RPMs. I suspect that for our purposes and the RPM
 > ranges we operate at that the smaller runners would be a better choice.
 > Opinions??  >
 >   How does the power output compare between your PP and bridge ported
engines?
 >
 > Mike Wills >>

 It was a long time ago, and I forgot how big I made them. I just now
measured a housing and Got these figures. Intake port, round, 1.710". This
turns into a square port inside. 1.695" X 2" tall.  The exhaust is round,
1.610" this turns into a square port inside. 1.640" X 1.40" tall. The power
from a periphery port would come on at over 8,000 and peak at about 10,000.
In sprint races some unnamed people were shifting at 10,700, and for long
distance maybe 10,000. A little steep for airplane use. In IMSA they were
using bored out carbs and 48mm chokes. HP would be 290 to 300 depending on
who built the motor. The bridge port has to run with 36mm chokes, so a direct
comparison I cannot make. Mr. Drummond's best with this size choke is 247 HP
at 9,400. These are 12A motors. His best bridge port 13B is 305HP at about
9,000. These RPMs are all down side for airplanes. However, if you make your
own ports you can move the best rev range way down. It may be possible to
replicate the timing of a stock 13B with a periphery housing and get the best
of both. Take a junk engine apart (free at some junk yards) and lay out the
port timing with a magic marker on the housing as you turn it over. At least
you can see if it's possible. The best engine ever built will run poorly if
the exhaust system is not properly designed. The biggest improvement I ever
made to one of these was to change my header from a 2" ID x12" primary to a 1
7/8" X 22" primary. That one change was worth 3 seconds a lap at two tracks.
I have yet to see in person, an exhaust header on a rotary powered plane that
looked like it would not deplete a large amount of power.  Lynn E Hanover

The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org