Here is a scale drawing of the Lemans engine showing runner
diameter and position of intake port in case you want to bore your
own p-ports. These are the dimensions we used on the current
test engine. Hopefully it is shortly ready for the dyno as Mazdatrix is 
building it as we speak. Well maybe not today.

This two is roughly the HP you can expect from
this configuration. The third plug was only worth about 3%
improvement in the BSFC.

If you dynoed the engine with a fixed length runner you would not see
this curve. That is because the Leman engine had variable length
runners. You will however see close to this HP with a fixed length
runner optimized for the RPM you choose. This is perfectly acceptable
for a fixed pitch prop. Variable length runners are only needed in car
applications.

You choose the best fixed runner length in the range of about 14 to
20 inches for the RPM where you want peak HP to occur. My guess for
7500 RPM is probably around 15 inches. This length will vary with
the diameter of the runner so smaller runners will have different
optimum lengths for a give RPM.

The runner tube Mazda used is slightly larger than 2 inch OD. I suspect they
used a metric size. Probably around 54 or 55 mm. Since metric or english tubing
in that size is hard to come by I used the closest size tubing
I could find and that is 2 inch .065 wall. Consequently I expect
a little less HP. We shall see shortly.

Paul Lamar
 
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