Jerry Hey wrote:

I exchanged a few e -mail with Rolf and, as always learned a lot.   One
thing I had not really focused on is that the reason the Leman intake
runners are two inch is because that is the size of the port.  If that
correlation is important then I should have a 1.5 inch runner.

As far as tuned intake runner lengths,  Rolf drew a distinction between
"ACTIVE" runner length and the length of the whole system.  The idea is
that the tuned length should be of one size so that the air moves
through it at a constant speed all the way to the p port.   Before the
tuned length,  larger tubes can be used to add length as the
installation requires.    I have drawn such a system.  Rolf has not
seen this drawing  yet and he might want me to make changes.   Regards,
  Jerry

This will be tuned at two different RPM's. One RPM is related to the
length and diameter of the pipes from the plenum to the ports and the 
other related to the length of the larger pipe going to the plenum.

As an electronic analog this is a series tuned tank or band pass circuit.

In this implementation the second pipe is so short and fat it will be 
tuned to a RPM range out of a normal operation of the engine. A similar 
system is used in the RX8 motor except the second pipe is longer and tuned 
to the proper range. The RX8 injectors of course are someplace else.

Since the tuned length of a runner is related to its diameter the smaller diameter
pipe needs to be even shorter than 17-18 inches. My guess is a tuned length 
of about 15-16 inches is about right. The center line length of the 180 is 
about 7.8 inches. Add two inches where the pipe comes straight out of the 
port and you have 9.8 inches. Add 6.2 inches for a straight section and 
the plenum is right on top of the motor. 

Also a smaller diameter pipe has a somewhat smaller tuned range. (Higher Q)
To broaden the HP RPM range the second 2" pipe can be about 19 inches or 15 inches
depending on whether you want to move the HP curve up or down. shorter will
give more power on the top end. Longer will broaden the curve downward. 
The peak power will suffer however.

Good luck getting the mixture the same in front and rear rotor.

Due to the smaller pipes the HP generated will not compare to the two
inch Russell manifold. The area of a 1.5 inch pipe is about 1.76 square inches.
The area of a two inch pipe will be about 3.14 square inches.
The air velocity in the smaller pipe is almost double so the skin friction
drag in the pipe will be four times higher roughly.
 
You have enough meat in your P-ports to ultimately open them up to an area 
equivalent of a two inch pipe.

Paul Lamar 

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