----- 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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