Paul,

 The publication, Street Rotary - How to Build Maximum Horsepower &
 Reliability into Mazda's 12A, 13B & Renesis Engines , states that  optimum
 header length for a P Port is 10 to 18".  Have you, with experience with
 the rotary run into this theory?

 Joe Berki
 Limo EZ

 It all depends on what RPM you want the HP to peek.

 22 inches gives us peek HP at 7500 RPM.
 That implies a 2.85:1 PSRU and a 6' dia. prop.

 If you are using a 2.17:1 gear box you want
 the HP to peek at about 6000 RPM however  you
 will get less HP. HP is torque times RPM.

 We verified this on the dyno and Mazda confirmed
 this in http://www.rotaryeng.net/Mazda_R26B_US.pdf

 You can download the paper and read it as a pdf.

 Paul Lamar


Paul,

The paper did not state how long the runners for the exhaust are on the
LeMans engine. I just thought that the 36" runners were optimum at 6500 rpm.
From what I have read in the paper it would seem that the intake runner
length is more critical than the exhaust runner length.

Joe Berki
Limo EZ

Correction on that stuff above. That is intake runner length.
I misread your message.

Here is the data on exhaust header length.
In our range 790 mm or 31 inches looks about right.
Coincidently that is what Racing Beat uses
in their headers they sell for the 13B.
Original Power Sport as I recall also used that length.

That is also what we used on the p-port 13B dyno test
but not the p-port RX8 engine as that is an entirely
different story with its simezed center housing exhaust
port.


15.3 inches or 390 mm also looks pretty good for
our speed range. Probably the second harmonic.

Paul Lamar