I don't know about you, but I'm confused!!
The sooner we work out the ideal port sizes the better !!
Please feel free to disregard all content, if it's too confusing.
George (down under)
You are not being too clear here George. Try a table.
Paul Lamar
George,
Where did you get the relative size numbers in percentages from?
I would assume the percentage numbers refer to area not linear diameter.
Am I missing something here?
Rolf Pfeiffer
Rolf,
Considering some of the engine inlet sizes change from model to model,
including the 12A -I compared MY 12A inlet AREA to the 12A Carby throttle,
trying to get a handle on what Mazda was looking to achieve in regard to
manifold sizes and losses from the inlet i.e. drag and turbulence.
It turned out about 17.5% difference between the carby butterflies and the
engine inlet - for the 12A I have. I initially calculated 20% for my own
installation ( Paul's suggestion) and it's pretty close.
I also have late model 13B housings which I have milled to see the
difference in the water jackets and oil passages - not a hell of a lot of
changes there but they do change for the RX8.
I was surprised to see that there wasn't much difference between the primary
( AREA) sizes of the early 12A and the later 13B, which leads me to believe
that too big a primary port may play havoc with idle - for a whole range of
reasons.
QUESTION
Paul or anyone- At what RPM does the secondary ports start to work?
Anyhow I then looked at the 13B secondary port and it was massive compared
to the 12A and massive compared to the difference in engine sizes 1146cc to
1308cc - only 14.13% difference.
So another conclusion is that the 12 A secondary port is undersized or the
13B ports are oversized OR both. Which means I can't just assume their the
ideal sizes and work my inlet manifold around the port sizing only. If I
were to do that I would need 60mm ID(2.36"ID) manifold tubes for the 13B -
way too big!
Excuse my rambling on!!
What to do next, I looked Paul's suggested manifold tube size and adjusted
the inlet sizing by 14.13% and it came out about to 1.5" ( 44mm ID -
14.13%). For the 12A that FEELS about right.
If I were to take Jerry's info of 1.5" - 14.13% =1.28" (33mm)- this is where
I get confused and don't know which way to go.
Attached is a couple of port size drawings I did for comparison.
Paul do you have something better on the 13B port sizes?
George (down under)
Better? Nothing better so far. Good work George. Here is what a third gen 13B looks
like compared to a 13B second gen. The history of the rotary has been ever larger port sizes.
The RX8 motor is larger yet.
Paul Lamar
Good project. Keep up the good work. Measure a 2nd gen 6 port and a third gen 4 port.
You might be able to go to Mazda dealer and measure or trace a low HP and a High HP
RX8 engine intake manifold gasket.
Paul Lamar
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