At one time I did measure the MAP
at the far end of the small (primary) runners and found a .8" Hg
drop at WOT compared to dynamic chamber reading.
At what RPM?
This is really what I was after; a feel for the pressure drop due to
flow losses, and trying to understand the nearly 4” Hg drop from
atmospheric that I measured at 6000 rpm. I am pulling both ports
through a 1.75” dia, 5” long TB barrel, and maybe a bit of loss in the
inlet plenum; but not likely that could account for such a large
loss. As you suggested, it must have something to do with the
placement of the measurement port. I may call the guy at TWM and
see what his thoughts are.
I expected this
drop. For reasons of not wanting to enter a prolonged and
fruitless discussion on rotary engine manifold design, I will not
explain why this drop is desirable : )
Oh; come on –
gives us the 25 words or less version – well; maybe 50 words. We promise
no prolonged and fruitless discussion.
Al
Damn, I'm such a sucker for that
line.
Most gear heads already
understand that successful intake tuning
is the art and science of maximizing and managing the energy represented
by the moving mass of air in the manifold as it accelerates and
decelerates. But, there are some less
obvious subtleties at work in the Mazda rotary manifold.
I believe Mazda's intent on the 2nd
gen NA rotary was to intentionally restrict the flow on the primary
ports so as to increase the velocity in the larger secondaries.
This goal is also aided by opening the secondaries a bit sooner than the
primaries (gets the train moving early). Note that porting
(enlarging) the primaries or making the primary runners
larger may be counterproductive here so the time honored
tradition of "bigger is better" will lead you the wrong way. The
resultant higher velocity in the secondary runners is then
used to increase VE with the later closing secondary port. So
why not close up the primaries completely and get even higher velocity
in the secondary? It's all about finding the point of
diminishing returns.
Tracy (way past 50 word
limit)
Tracy's analysis sounds reasonable to me.
Its clear that Mazda expected some benefit in going to the trouble and
expense of keeping the primary and secondary runners and port timing
different. I had wondered why they would have the secondary port
open before the primary port (6 port engine) and I think Tracy's
hypothesis is probably correct - at least it makes sense.
I ported both my primary and secondary to the same
port timing and concluded that since the ports now had the same timing
that I could merge the secondary and primary ports with minimum adverse
effect. My testing will hopefully show that to be
correct.
Ed Anderson
RV-6A N494BW Rotary
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