I keep reading about the 5th and 6th ports and you guys are mixing in other talk about if you remove the cat it effects it etc. . . I think I should stick to cars with pistons

Basically if you can give me a description of what the ports are/do and why they are effected if you modify/delete the cat, and the air pump as well. I have a rough idea of how the rotor works as far as intake, compression, igniting and exhaust. These cars seem to be more wrapped around computers and sensors then a space shuttle

 

http://www.rotaryengineillustrated.c...-ports101.html

 

Okay, you know that the intake ports of a rotary engine are opened and closed by the motion of the rotor, and the size and shape of these ports dictates the rotary's equivalent of "lift" and "duration", right?

In 1984, Mazda introduced a 6-port 13B. You still had the "standard" four intake ports (two per rotor, one on its respective endplate, and one on the center plate), but Mazda added two more, each on an endplate. The "original" ports are called the "primary" intake ports, while the new ones are called the "secondary" intake ports.

The secondary intake ports open after the primary intake ports, and act to extend the amount of time that the intake ports are open ('duration'). They also increase the total flow area of the intake ('lift') for better breathing. It's like VTEC for rotaries, only much, much simpler.

These ports are controlled by rotation of "sleeves" in the endplates which operate to open and close these ports. This rotation is performed by vacuum/pressure actuated "solenoids" (they act just like wastegate actuators), and are set to open the secondary ports at ~3500 RPM.

In the 84-88 13B engines, this pressure (routed to the actuators) comes from exhaust backpressure (they're sprung for ~2 PSI). Thus, one can see how elimination of the cats (which reduces backpressure) would interfere with the operation of the system. In the 89-91 13B, it's operated by pressure from the airpump. Again, if you eliminate the airpump, they won't open correctly. Also, these sleeves are in the intake stream, and very near the engine. As such, they tend to get pretty gunked up, and if not opened up enough (i.e. moved by 3500+ RPM engine operation) can get stuck closed, opened, or half-way between. (That's one of the reasons that we recommend daily visits to redline in an N/A )

Hope that helps...

Brandon

P.S. The pre-3rd-generation RX-7s are very simple cars. Most everything is mechanical in nature. Only in 1989 did Mazda barely start to move toward more electromechanical systems. Look ma! No sensors!

 

Yeah, that pretty much sums that up.

 

Good description, except the original four ports are called the primary ports (on the centre plate) and secondary ports (on the end plates), while the additional ports on the end plates are called auxiliary ports.

To expand a little on their purpose, it’s important in both piston and rotary engines to keep port velocity high. This improves air/fuel mixing and torque. So small ports are good for making torque at lower revs, but are too small to make good power at high revs. The opposite is true for big ports. The 6-port system means you can have small ports at low revs, and then open the aux ports to effectively make big ports at high revs. This is exactly what Honda’s V-TEC does with it’s two different, switchable cam profiles.

 

Er, doh.

I knew I had that wrong.

Brandon