Wes,Originally Posted by monsterbronco
The 6 port induction system (5th-6th ports) is on all 2nd Gens, 86-88 (S4) controlled by exhaust and 89-91 (S5) air pump. The VDI (Variable Dynamic Intake) is on the 89-91(S5) upper intake manifold as the 86-88(S4) had a completely different intake design.
5th and 6th Ports (Aux ports) and VDI
All non turbo 13B engines used in the 2nd generation RX-7 have a 6 port induction system. The 5th and 6th ports remain closed below about 3500 RPM, preserving air velocity and running more conservative port timings to help increase low end torque. After that, the ports open up and improve top end horsepower. If the ports are not working properly, you will loose quite a bit of top end punch (the commonly accepted figure is around 25 HP). To test them, first locate the actuators. They are located on either side of the ACV valve above the exhaust manifold. Looking from the passenger side of the engine compartment towards the drivers side, you will see two cylinders with rods sticking out from them. Those are the actuators. Smear some grease on the shafts and after your test drive look to see if the grease has moved. If it has, then the actuators are working. If not, something needs to be repaired. If the car was not driven at high RPM, then most likely the actuators have frozen from age. Removing them and applying penetrating lube usually brings them back to life. If the actual port valves are stuck, the intake manifold probably has to come off. The '89-'92 engines also have a Variable Dynamic effect Intake (or VDI). This is another valve in the upper intake manifold that opens above about 5000 RPM to allow the pressure waves generated by intake closing to travel through the secondary port runner to the opposite port and force more of the intake charge into that rotor. The valve remains closed at lower RPM to make the secondary runners longer, thus maximizing torque. This actuator is located on the drivers side of the upper intake manifold between the runners, just below the dynamic chamber (plenum box). It can be tested in the same way as the 5th and 6th port actuators. Just make sure you make several runs over 5000 RPM so that the intake valve can open.
Also Read here...
F42-47
http://www.rx7city.com/Manuals/89-91...mission_NA.pdf
Spend some time on RX7club.com in the 2nd Gen section and reading the FSM (online for free if you don't have one), you'll learn a lot about the car. And of course, get your hands dirty and work on it yourself. Both of these systems give the car benefit at low RPM (below 5000k or so), therefore in a racing application they are not needed and removed.
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