X-Mozilla-Keys:                                                                                 

I had a question about the construction of a peripheral port that maybe Paul
Yaw could answer. The drawing for the Power Sport engine shows the placement
of the port between the two bolt holes in the rotor housing. It would seem to
me that the angle of the port tube, relative to the horizontal plain of the
rotor housing, would greatly effect the port timing. So...At what location,
on the inside of the rotor housing, should the port pass through the steel
liner?

Assuming that the passage was straight all the way through it certainly
would affect the port timing.  The passage flares out after it enters
the housing. I have some Mazda paperwork showing the effects of port
window area independant of runner area etc.  Their paper shows an
increase in VE throughout the powerband with a VERY large window.  A big
rectangle to be exact.  I think that pretty much everyone is using a
rectangular intake window, but I don't know what Powersport is doing.
There is enough material in there to move the port timing a great deal,
and the end result is a port window which is much taller than the inlet
runner.

My problem with the angle of the inlet tube is the direction of the
airflow.  Since the point is to fill the "top" of the rotor housing, and
the rotor is sweeping everything in that direction, it makes no sense to
me to point the runner downhill.  Racing Beat has the runner going down
towards the bottom of the engine.  The factory pieces go in straight.  I
think Paul has a picture on his website.  If you happen to live in a
University town, you can probably find old SAE papers on microfiche at
their library.  There is a ton of good information there.  Especially
the papers written in the eighties.  As for where it should enter, you
can partially assemble an engine with a degree wheel attached to the
shaft, and mark the housing for intake opening and closing. Just center
the tube in the middle of the port window and blend everything with a
grinder.

Check out SAE #900032, for a great paper on peripheral port engines, or
#880625 for some really cool pictures of the flow patterns in a running
engine.  It's better than Playboy I promise.

Duh!  I just noticed the pictures that Paul attached to your message.
That should explain everything.

PY

 
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