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Hi Mark,
Yeah, I thought you might find some interesting and
potentially useful data in there. Not many books commonly available on the
Rotary engine even mention PP. This one also has some useful analysis (as
you pointed out) on the PP.
I agree, its money well spent if you are going to buy a
book on the rotary.
Ed
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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