Jerry Hey wrote:

I just got of the phone with Jim Mederer at Racing Beat.  I had
called inquiring about using one of his exhaust port templates with
my P Ported engine.   He said the "Street" template would be
appropriate, however he went into great lengths to tell me why in his
opinion we were going in the wrong direction with the 6000 rpm p.
port engine.  One point he made was that p ports are most efficient
above 8500 rpm.   At that rpm p-ports are generating over 300 hp.  I
told him that Power Sport was getting 215hp at 5300 rpm and he said
he believed it but that side ported engines would deliver the same hp
much better.

  He was not talking about 6 ports.   He thought the right way to
build an aircraft engine was to take the side housings from a Turbo
four port and use them with the rotor and  housing from a NA 6 port
which has higher compression. Only a small amount of die grinder work
is then necessary to achieve 200 plus hp.

Jim went onto say that if we do build  a p port, that we should keep
the ports   small to maintain good velocity.  I tried to get a
recommended size from him but all he would say was that 1.75 inch
diameter was too big for our target rpm.   He felt that the port
timing of a p port if  transferred from the side ports per Lynn's
suggestion would have too much overlap.

Another point he made  surprised me because he said it would not be
sufficient to secure the sleeve with DevCon only.   He recommended
threading the sleeve in  and  also using DevCon.

Even though Jim Mederer has not built rotary engines for aircraft,
his experience and expertise in building rotary race engines,  make
his words carry considerable weight.

Right now,  I am still committed to p porting my engine, but am
worried about port timing and size. Paul,  I have the feeling that if
you were to talk to Jim and to Lynn and gather all the data you could
design an aircraft p port engine that we could build with confidence.
This is way beyond my level.

  I wish we could read Everett Hatch's notes on the subject.

   Jerry

I am rather surprised that Jim feels that way. I am willing to bet
he never tried an NA P-port with long intake runners as used on the
Leman engine and the Power Sport engine. He has had no reason to
do so unless he has been commissioned by somebody to build a P-port
engine that would never see more than 7500 RPM for some strange
reason (aircraft use). Most race car situations put no such limits
on RPM. Everett Hatch at Power Sport on the other hand had every
reason to do so. Everett had two dyno's. A conventional
al dyno and a prop type dyno. The current Power Sport also has a dyno.

I don't think Jim was directly connected with the Leman effort. The 
vast majority of racing car engines use short runners to get peak 
power at 8500 to 10,000 RPM. Variable length runners are now outlawed 
in road racing. Why? Because they work that's why. We never ever 
run the engine over 7500 RPM so longer runners are called for
such as used on the Leman engine at 6000 RPM. 

I get the impression that Jim reads very few Mazda SAE technical papers.
For example, according to this chart, the Leman P-port engines
spent a good 20% of the total time between 6000 and 7000 RPM.
No way would a road race driver tolerate an engine that bogged down
at 6000 RPM. The Leman engine had about the biggest P-ports
you can imagine but it also had very very long intake runners 
at 6000 RPM by rotary race motor standards.

My contention is the length of the runners is the most important
factor. Not the size of the p-port. Bigger is better in almost
every case. Rotary engine ports have been getting bigger and bigger 
over the years. The RX8 motor is the last example with 20% larger
ports.

In this picture the length of the intakes pipes are twice as
long at 6000 RPM.

Paul Lamar
 
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