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
George,
I can't be 100 % sure, but I believe the 86-88 6- port secondaries open at
3700 - 3800 rpm.
Most of these high mileage cars develop an acceleration stumble at this
point , most likely due to carbon buildup on the secondary barrels causing
them to delay opening and messing up the EFI timing.
Mine does it also untill it's fully warmed up, then it goes away.
I don't know about the 89-91s.
Ron Freier
Vision 4-place w/ 13B turbo
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