wd6681

As certain I am the answer to this question is obvious; searches have netted me no answer. Lets simplify my question to a 4 port setup like that found on the 12a. As a brief disclaimer, I have never disassembled a rotary so my technical information is photo driven.
a 2 rotor engine with 4 ports has the following configuration, correct?
1 large runner in each of the (2) endplates
2 smaller runners in the center plate
now each rotor housing is fed by 2 ports -the large one in (1) endplate and (1) of the smaller ports in the centerplate-
If this is correct and I understand correctly, the termination size of these ports into the housing is the same size and timing as its freind on opposite side of the rotor housing (endplate port vs centerplate port).

Should all of this be accurate... Why are the ports shape and size at entry point from manifold to plate different? (centerplate ports being the tall and narrow variety with endplate ports being fat and large).

The relevance of this questions applies to intake and carb setups. Of course one could do a twin choke carb/(2) single choke carbs each feeding a rotor by siamesing the flow of (1) centerplate port and (1) endplate port. But supposing one wanted to complicate this and 4 single chokes were run, isnt the flow @ the centerplate ports lower? If it is, what about siamesing the (2) centerplate ports into 1 carb? Ala 3 carbs on a 2 rotor.
Furthermore, why did mazda do this smaller, larger port configuration?

wd6681

is this my answer?

j9fd3s

iTrader: (3)

basically the way the ports have evolved is from having the "4 port" configuration, like a 12A, where all 4 ports are the same, to having the "6 port" configuration, where all the ports are different is to have better low end power, throttle response and keep the top end power.

when they started making the primaries smaller, with the EFI engines, velocity improves at low engine speeds, and throttle openings which improves the low end. the secondaries stay the same, and then they add the 5th and 6th ports to gain top end power.

the Rx8 takes this to the extreme, where it only runs on the 1st 2 ports at low rpm, then opens the 3rd and 4th, and then 5th and 6th, and each pair of intake runners actually has its own tuned length.

wd6681

All of that makes sense. However the ports on my 85 12a are not the same size. Although I cannot speak for their shape and size where they terminate into the rotor housing; their cross sectional area are not equal (endports vs center). It is now my understanding that the center ports or 'primary' ports are smaller and timed earlier for high velocity while the endports or 'secondaries' are larger and later in the rotor cycle.

diabolical1

iTrader: (3)

if the engine is not apart, then you're only looking at the runners. i can't speak for area (though, i suspect they're probably the same), but they are shaped differently. secondaries are shorter and rounder.

wd6681

So theoretically a 4 carb setup is viable. The 'primary' center ports are simply tall and narrow at their entry because they are next to one another? Does anyone have photos of stock 12a primary and secondly ports on the inside of the motor?

diabolical1

iTrader: (3)

4 carbs? as in ... one for each port? my first question would be WHY?

i guess the simple answer is yes. it is theoretically possible. however, i am old enough to remember the nightmare of trying to tune and synch twin Webers back in the late 80s and early 90s on rotaries. i can only imagine trying to go with 4 singles?

for a photo of a stock port, locate my porting thread. it has a primary or secondary port, but not both (because they were the same). you can also check out Ray Green's 12A thread, if i recall, he has a variety of housings featured in it.