Rotary Resurrection - Tech Section

ON nonturbo 13b engines after 84, mazda designed a variable intake system using 4 constant intake ports and 2 auxiliary ports (6th ports) which are supposed to open around 3500-4000rpm for better midrange and top end power. The ports themselves are 2 hollow cylindrical sleeves inserted into the ports in the block, each connected to a rod that runs out the lower intake manifold and rotated by an actuator. There is a port cut out in the side of each sleeve, and when rotated by the actuator and rod, the hole in the sleeve aligns with the hole in the engine block’s port, and opens the way for airflow. Between 3-6psi of airpressure is needed to operate these actuators.

ON 84-88 cars, this air pressure came from exhaust backpressure, from stock catalytic convertors and mufflers. A tube runs from the main cat back to the engine, and from that pipe a small vacuum hose runs to the lower intake manifold, which applied pressure to the actuators. This is not a great way to accomplish port actuation. After all these years, most exhausts either leak or have been modified, reducing backpressure and possibly making ports operate poorly or not at all. Even when new, the system wasn’t the best. ON a turbo car, boost is usually higher in the higher gears, because there is more load on the engine, and it moves more air, driving the turbo harder. Though a nonturbo engine doesn’t have a turbo to amplify this effect, it still occurs…the engine will move different amounts of air depending on the weather and the load. Since the port actuators require a fixed air pressure to open, it stands to reason that they would actually open at different times.

ON 89-91 cars, the system was set up much better. Pressure from the air pump on the engine was routed through the emissions rack to vacuum solenoids which the ecu switched at the proper time to actuate the ports. Though this is a nearly bulletproof system, sometimes it must be re-engineered, specifically if the user removes the emissions rack and/or air pump. Note that it’s generally best to leave the stock system intact on the 89-91 engine, IMO.

This writeup is focused on the 84-88 engines. The same ideas apply to the 89-91 cars, with 2 major differences. First, there is no method to control the electric air pump on the older cars…there is no ecu trigger, or other trigger that can be used. So, these owners must set up their own trigger system. The most popular way is to get an MSD rpm switch, and a 4000 rpm pill, and this generates an rpm sensitive electrical trigger signal that can be used to switch the air pump off and on. Second, the 89-91 setup in this writeup also uses a VDI intake valve on the middle intake. Owners of older cars need not worry about integrating this valve and solenoid into their electronic setup.

TO do this conversion, you’ll need some 5/32” vacuum hose, some tees, a 12vdc automotive relay, 16 gauge wire, wire terminals, one of the stock vacuum solenoids found on the engines, and a 12vdc air pump. Here is the one I found to use with this conversion.

To do this conversion...

1)’ll need some 5/32” vacuum hose, some tees, a 12vdc automotive relay, 16 gauge wire, wire terminals, one of the stock vacuum solenoids found on the engines, and a 12vdc air pump. Here is the one I found to use with this conversion.
You also need an MSD rpm switch and a set of pills in the appropriate range (4000-4500) as well as wiring to install it.
IF you rarely push your car hard for long periods of time (more than 5 minutes) you can use something like an air horn motor. For extended periods of use, you;ll want something stronger, like a small tire air pump. I use a 12vdc air pump available for $15 from walmart.

Take the plastic case apart and remove the actual pump. You’ll cut off the factory wires, you;ll also want to keep one of the rubber vibration dampers.


You’ll have to modify this particular air pump to work properly…as it is, it generates too much pressure and could even damage the actuators. Remember, you only need a max of 10psi to open these actuators, actually 5 is sufficient.

I removed the extra wiring, leaving only a positive and ground lead. Also cut the end of the hose off since you cannot use it. This particular pump had a gauge attatched, and I have removed it and placed a vacuum cap over the open nipple.

I removed the “head” from this unit, and found 2 valves, an intake and exhaust.
I used a small screwdriver to turn the spring loaded exhaust valve so it was constantly open..this would allow some of the generated pressure to be vented back into the cylinder, reducing overall efficiency of the pump and safeguarding the actuators.
Reassemble the motor
Moving to the rpm trigger, I cut the appropriate wires for function with rotary tach signal per the instructions. Always refer to the directions with your actual unit before doing so.
Here is the standard automotive 4 prong relay.
Here’s one option for mounting the units. Ignore the existing wiring, which was already installed by the customer for some sort of foglights.
Connect the MSD’s yellow ground wire to the relay. A relay has 4 terminals. 2 of which are low amperage trigger…one ground, one power. The other 2 terminals connect together when the first 2 receive power and ground trigger. Connect the yellow wire to the ground trigger terminal.
Connect the MSD red wire power input to the switched power output of this unused plug by the leading coil. The correct terminal is directly adjacent to the notch on the plug (this applies to 2nd gen cars, you’ll have to find your own switched lead on other models).
Here the MSD rpm lead is connected to the leading coil tach signal..
Here is one of the best places to pull high amperage battery power from…the back side of the main fusebox, which is protected by the 80A main fuse. You can also go directly onto the battery terminal, with an inline fuse.
This is the same wire on the other end, with another smaller wire jumpered off it. This will provide power to 2 terminals on the relay.
Connect these to the relay…one as the trigger positive, and the other can go to either of the remaining terminals.
The remaining terminal will supply power to the air pump and the solenoid.

Find a place to mount the motor where the moving parts will not be interfered with. Keep in mind the motor vibrates a lot so it needs to be secure. You may experiment with using the rubber dampers that originally came with the motor in it’s plastic case, or just install it however.

Run a wire from the remaining terminal on the relay to your motor. This wire needs to supply both the motor, and the vacuum solenoid, with power, so it needs to be tee’d somewhere along the way. Ground the motor as well to a frame location nearby, and this ground wire also needs to feed the solenoid we’ll be using.
Here is a standard vacuum solenoid from an 86-95 engine. Some of the solenoids have removable air filters on one terminal, some do not. IF yours has an air filter, remove it.
The input of these solenoids is the top port. The lower ports are output and vent to atmosphere and are connected when the solenoid is off. Use a mityvac/air pump to test them (once with voltage on and once with voltage off) or just  blow through them. This will verify which ports are “connected” at which times. Of the 3 ports, only 2 are “connected” at any one time, the solenoid is just a switch between which ports are connected. When the solenoid is off (below 4krpm) you want the 6 ports to be vented to atmosphere (or engine vacuum as described below) when it is turned on (above 4krpm) you want the 6 ports to be connected to the air pump port.

Tee into the vacuum hose at the pressure sensor. Run a vacuum hose from the 6 port nipple as well.

Connect the tee from the pressure sensor to the solenoid…
Connect the solenoid to the air pump…
The remaining port goes to the 6 ports themselves
The top and one side ports are connected when no power is applied. This means engine vacuum is pulling the 6 ports shut. When power is applied, the top port switches to the other side port, which is the air pump supply…air flows through and opens the 6 ports. When you shift or drop below 4k, the voltage is removed, the solenoid switches back, and the engine vacuum again pulls the 6 ports shut quickly for best response. Note that any leak in the 6 port system can cause an engine vacuum leak and problems at idle.

Supply power and ground to the solenoid (from the motor wires). Here I used a spare cut off plug from a parts harness, but you can simply use 2 female terminals. Polarity does not matter, in other words it does not matter which terminal gets ground or power on the solenoid.

Test the system by revving the engine above the pill RPM and see if the motor turns on and the ports open.
Rotary Resurrection - Tech Section
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