Well, first there is the perceived low speed or idle problem. When
the
engine idles, any engine, the throttles are closed and a high vacuum
exists in
the intake manifold.
No problem. In a piston engine, there is a valve in the way, the open
periods
are short, as is the overlap (intake and exhaust open at the same time).
The
amount of exhaust that can be sucked into the intake system is small.
Not so the Pport rotary. Both intake and exhaust are large free flowing
holes, sitting close together, the exhaust is at high pressure at the
beginning of
each of these cycles, the 20 inch or so runner is at high vacuum. Good
luck on
that idle problem.
The butterfly mounted close to the housing shuts off the long intake
runner,
so that the exhaust gasses "see" only the volume of the combustion
chamber. No
more long vacuum tube.
Instant better deal. The idle should be at the least acceptable.
This is has only to do with the long runner of the intake system that is
tuned for 6,000 RPM to 6,500 RPM. It is far less a problem in a race car
with very
short runners tuned for 9,000 RPM.
Once the engine is spooled up, (with the ideal exhaust and zero back
pressure
muffler) the exhaust is leaving at supersonic velocity and leaves behind
it a
slight vacuum. So the overlap that makes it a dog down low, is making it
a
Bear in the operating range. The low pressure in front of the inlet
runner pulls
mixture down the face of the rotor near the 100% mark, and instead of a
loss
we get a bonus amount of mixture. That is called "blow down." The added
velocity can overcome more of the reverse flow and overfill the chamber.
The open and closing points are of little interest until a base line is
established. Only one company has so far pulled this off with any degree
of
success. It would be nice to know what their ports looked like, and what
the event
timing was.
I think it would be difficult to beat a 13B Pport engine down to 200HP
at
6,500 RPM with almost any port shape. The advantage of the single big
port is
that one big runner has a lot less drag than two little ones. Even a
Cosworth has
one big runner feeding the two intake valves. The runner breaks into two
runners just above the valves. Tuning the length may be a bit harder,
but it will
work great, right out of the box.
Great care in the exhaust system to prevent back pressure is a must.
The first time my driver came back from his first session behind a Pport
12A
(about 275 HP) he had planted the throttle while crossing the apex of a
fast
sweeper and passed through the (sweet spot at 100 plus % power) and got
wheelspin in third gear. On wide sticky slicks. Having never gone off
there before,
he could not remember how far it was to the guard rails or if there were
tires
stacked in front of them. It is so hard to see when you are spinning
like a
top. There are no tires, but plenty of grass. No damage and a new
respect for
the engine.
Lynn E. Hanover
Lynn,
Good stuff there Mate,
The main reason to consider PP ( in my case) is that the aluminium end
housing Butch and I are working on would be so much simpler to seal without
a side inlet and I would guess that would be true of Richard Sohn as well!
I will rehash your words and ask some more questions later if you don't
mind!
Your comments on the PP idle was enlightening, I suspected that the
butterfly close to the port wasn't the 'fix it all solution' some claim.
BTW do you or any one have the details of the port timing of the Renesis -
that might be interesting !
I also had a bit of a problem finding the exact spot to mark TDC on the
e-shaft as the aluminium angle was in the way. I used a feeler gauge to find
equal distance between the aluminium
and the shaft marked each side, halved the distance and figured that was
the middle (TDC).
Not being entirely happy with that, I marked the horizontal centre ( 160mm
from the machined bottom) and vertical centre (135mm from the machined
manifold side) on some tape (stuck to the end plate). I then replaced the
housing rotor and shaft and sighted down the apex seal groove, to get my
mark dead centre of the groove.
I checked TDC and BDC and they were spot on - it was a good check though!!
Also the TDC appeared to be centre of the keyway on the shaft - all being
equal TDC is where it should be!
I haven't got TDC marked on my pulley only 5 and 20 degrees, so I will have
to do that yet.
Another thing I did was to make a clear plastic pattern of the rotor to put
in the housing (to play with). It helped me to get some orientation on how
things worked.
George (down under)
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