17 inch is right from port to dynamic chamber for both 3000 and 6000.
At 3000 RPM the pulse travels 34 inches from one
port over to the other while at 6000 RPM it looks like two simple
17 inch runners and a somewhat restricted plenum chamber.
This is about the stock 3rd gen configuration.
As I said low RPM torque is their biggest problem
If yours is 17 inches from side housing port to side housing port it
is
primarily tuned broad band for about 6,000 and 12,000 as simple pipes.
Here are a couple of shots of the third gen dynamic chambers.
Mazda claims they are a large improvement over the 2nd gen versions.
The main improvement is putting the air feed pipe/throttle body in the
same
plain as the runners more or less. The 2nd gen feed the air
in at 90 degrees. They could not quite pull it off on the
inner loop as you can see here. It goes in at about a 45 degree
angle. I noticed that Able Ibarra with his 800 HP turbo third
gen 13B engine uses this stock manifold that has been extensively
extrude honed.
This is a fascinating subject to me and I am sure Mazda spent millions
researching this stuff.
Paul Lamar
I agree, fascinating indeed - Ok, looks like my 21" from port to
dynamiic
chamber vice 17" is a bit long for 6000 rpm which probably explains why
my
peak torque appears closer to 5700 rpm than 6000. I will shorten this
one
from the current 21" to around 18" just to see the effect. Can always
shorten it another inch or so {:>).
Too bad we don' t have the resources to research/experiment/test to
determine optimum for aircraft use, but considering what we get its
fairly
close with the Renneses even closer to the perfect power plant.
Got a copy of Flying Magazine, Peter's article on the rotary engine
referes
to you as the "Spider at the center of the web" {:>).
Ed
Yes I know :(
Can you shorten it to 8.5 inches? That would be optimum for
the manifold to actually work as a dynamic chamber. At 17 inches
and 6000 RPM it is working as four tuned pipes (two at one length
and two at another length) feeding off two piss poor plenums :)
At 17 inches it is working as an actual dynamic chamber only at 3000 RPM.
As far as the slightly different lengths are concerned an electronic
analogy would be two series resonant circuits tuned
at slightly different frequencies in parallel. The impedance would
be lower if they were both tuned at the same frequencies
and the bandwidth narrower.
Hopefully Jerry Hey will have a p-port engine running soon
and it is easy to vary the runner length so we may have some dyno
data on this soon. The dyno is close to being done. All I need now
are some engines to run on it.
Paul (Spider) Lamar
Gee, Paul, if I shorten it to 8" from port to plenum that will only leave 4"
for the tubes, heck, might just as well bolt the throttle body to the
manifold casting and be done with it. {:>).
You would think so at first glance but it is really different than that.
To make certain we are both on the same choo-choo train. Are you talking
about shortening my proposed 18" total distance from port to plenum to just
8.5"? which means basically taking 9.5" out of the tube length?
Yes.
If so, I
think I will decline. While I am not certain all the reasons, when I had a
short intake manifold (with bigger throat) my performance really sucked.
Performance problems were not necessarily related soley to the orginal
manifold, but I am not inclinded to go down that route again. Let someone
else carry that ball. {:>)
I know this is hard to believe and it took me a few years to figure out
what Mazda was doing as they never fully explained it. There is a subtle
difference in what you are thinking about above and what a true dynamic chamber tuned
for 6000 RPM looks like. It would look something like this 3D rendering.
Yes it is ugly but that is what it must look like to be a true
dynamic chamber at 6000 RPM. The intakes are missing in this quick
and dirty 3D. Also it would have a 90 in it if you used my casting.
The second 3D is a slightly different version but it has the air intakes.
The objectives I had for using your casting were:
1. Clean up the runner interior air paths (the old one had bumps, plugged
inejctor holes, not to mention some convoluted turns in my plenum {:>))
2. Move the secondary fuel injectors away from the exhaust manifold (also
possible better BSFC)
3. Clean up the manifold/block area for possible installation of
turbocharger
4. Try Plastic Resin casting of plenum/throttle body/injector bosses
5. Make it possible to try larger Throttle body
6. Knock off some of the weight of my current boat anchor intake.
I hope to get the weight down from the current intake system's 21 lbs to
around 10 lbs - we'll see.
The tubes are slightly bigger in diameter than my current intake as I used 1
5/8 secondary and 1 1/2 primary. So hopefully some of the clean up, bigger
tubes, etc, just might translate into small power gains. But, so long as I
don't lose what I have in performance, I'll be pleased.
Ed
What you need then if you are unwilling to take the leap of faith
to a true dynamic chamber tuned for 6000 RPM is four equal length runners
17 inches long feeding from a 180 cubic inch plenum with bell mouths. I was kind
of hoping you would be a bit more adventuresome :) I suspect the light bulb
will light any minute. I feel I am getting warm :)
Paul Lamar
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