| Joe,
Sorry, while the author goes into great detail about the other intake designs, it barely touches on the p-port intake. There is a chart that shows the length of the 787B LeMans engine. As you may know, Mazda used a variable length intake. There's a graph that shows that runner length was +175mm at 6000 rpm, and +125mm at 7000 rpm. However, it doesn't state the overall length, or the length of the fixed intake tube. (Maybe someone knows that number) So, if you know the fixed length, you can add either 175mm for optimization at 6k rpm, 150mm for 6500 rpm, or 125mm for 7k rpm.
Using calipers, I measured the width of the rotor housing in the drawing and extrapolated to get the length of the fixed intake tube on the 787B motor. My measurement gives approx. 16" (rotor housing to end of bellmouth at its shortest setting). Adding 150mm (5.9") to that (tuning for 6500 rpm), and 1.5" (rotor face to outside rotor housing), I came up with a total intake runner length of 22.4" (bellmouth to rotor face). Or, subtract 1" for a max torque at 7000 rpm. While just a SWAG, this is close to what I've read previously.
Mark On Wed, Dec 1, 2010 at 4:10 PM, josrph berki <jskmberki@windstream.net> wrote:
What does it say about intake runner lenght for a P
Port? What happens if the exhaust header length is longer? Can it be
tuned. 10 to 11 inches is pretty short although a collector could make the
transition and get the hot stuff out of the cowl.
Joe Berki
Limo EZ
----- Original Message -----
Sent: Wednesday, December 01, 2010 11:36
AM
Subject: [FlyRotary] Re: Modified header
Calculations
Ed,
It took a while, but my copy of Street Rotary - How to Build
Maximum Horsepower & Reliability into Mazda's 12A, 13B & Renesis
Engines finally arrived yesterday. Thanks for the
recommendation. Lots of good info, everyone on the list ought to order a
copy and read it from cover to cover, except for Lynn H. - he ought to
write his own book on rotary engines. (I'd buy the first
copy.)
As you suggested, I've been reading the chapter on exhaust systems.
I found a paragraph that is right on target relating to what we've been
discussing (exhaust system restriction). They compare a 2-rotor wankel
to a 2 cylinder 4-stroke where both cylinders share the same
exhaust port.
Quote, "...the exhaust system on a 12A or 13B rotary engine is roughly
analogous to a two-cylinder piston engine in which both cylinders are served
by a single exhaust port. If cylinder #1 was in overlap period, and the
exhaust valve of the #2 cylinder then opened, high pressure gas would flow
from the #2 to #1 cylinders. A highly restrictive exhaust system would
aggravate the situation. This, the authors point out, is the major
reason why a free-flowing exhaust system is so important in a rotary
engine." This explains why I saw such an improvement when switching
exhaust systems.
There is also much discussion on primary header length.
Disregarding the "long" header system as we don't have the room, the "short"
header length shown for a p-port engine is between 10 and 18 inches. So,
your calculations for header length seem to be right in the ballpark.
Now I have to figure how to get the three very short primary tubes of 11 3/4"
to meet on the same tangent at the collector.
Finally, I liked their comment regarding the peripheral ported
engines. It reads, "Traditionally relegated to speciality
race cars, occasionally a peripherally ported engine finds its way onto the
street in some high-performance vehicle. These engines are not, however, for
the faint of heart." LOL Not to worry, my heart is
strong!
Mark
On Sun, Nov 21, 2010 at 7:53 AM, Ed Anderson <eanderson@carolina.rr.com>
wrote:
Mark,
I did some additional reading in the rotary book I
recommended to you and a bit more head scratching on exhaust
systems.
I modified the tube length formula I used
earlier to compensate for the fact the rotary puts out two exhaust pulses
per port per 720 deg cycle compared to 1 for the piston engine. This
in effect halved the length of tube needed to get the same scavenging
effect.
Also using the recommended rotary book values
for area of a rotary exhaust tube , I calculated the tube diameter
which came out to 1.8".
In any case, I have attached the spreadsheet with
those modifications
Ed
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