George Lendich wrote:

Paul,
I was surprised at that BSFC also - what would it be leaned ?

You may very well be correct with your assumption on the better
breathing
compensating for the exhaust gas 'overlap' mix. However they may
have
a
little bit of housing ( inlet) shape that we don't know about,
which
would
help here also.

All that need to be concerned about  now is the back pressure and
as
, if
you say, the closer butterfly compensates for the backpressure, as
Richard's
6" manifold clearly demonstrates, with resulting 1,200 rpm smooth
idle.
George (down under)

There is nothing trick about the Lemans engine housing shape.
It is a more or less a large mostly round hole. You can scale the
port diameter and timing from this drawing.
I never understood why people could not understand that while for
the last five years we have been talking about the Lemans geometry
and port timing. I think I mentioned it many times until I got
tired of mentioning it over and over again. You can also scale the
fixed length of the runners and add the lengths from this chart
for any RPM between 6000 and 9000.

The butterfly does not compensate for the exhaust back pressure HP
wise.
You still need to keep the exhaust back pressure down if you want
good
HP.
6.5 inches is not close for the butterfly. The Power Sport engine
has the butterfly in the rotor housing. Richard's engine is not yet
tuned
with long runners so the jury is still out on the quality of the
idle.

Paul Lamar

I scaled out this drawing two years ago and I still have the
drawing.
It is not that hard to do if you have a program like Pagemaker (now
InDesign).  The Leman p port was constantly on my mind as we
designed
our implementation.  Our port is smaller and opens later which
should
help with the overlap.   I expect to have better BSFC than the Leman
engine at our RPM for this reason.  The main difference between the
Leman  engine and  stock is the additional spark plug.  .      Jerry

The thrid plug was worth about a 3% increase in torque and a 3%
reduction
in BSFC. Hard to measure. More like 2% in the 4500 to 6000 RPM range.
SAE paper 920309.

Paul Lamar

Jerry,
I can't say this enough "Your doing a great job!".
I'm very excited to see how your P-Port works.
My approach will be a little different from yours as I will have a
inlet
more closer in shape to the exhaust port shape - hopefully !
This may require a cast insert, to get the flow characteristics I
want.
Keep up the good work.
George (down under)

George,  A number of people who I respect have suggested that the
optimum shape would be more rectangular.  Making the port wider is only
way to get more volume while at the same time retaining the timing  you
have selected.   I would have done the same except that according to
Rolf's calculations the 1.5 dia. hole  is  adequate up to 8500 rpm.  So
why bother.   I think the round hole will be easy on the seals.    Jerry

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