 Rotary Engine Porting
Standard Port
 Standard ports, stock ports, are best described as a compromise between emissions, fuel economy, and power. The first rotaries were freer to making power, but there was less knowledge at that time to make the most of the ports. In general it is possible to get another a ten percent increase in power though the standard port of an atmo inducted rotary engine. Modifying on a budget? Remember that all pre-1986 rotary plates and rotor housings are interchangeable - so if necessary mix and match for best results.
Even though the standard port is stock, significant power can be produced by simply adding exhaust and induction modifications. Did you know that Formula Mazda cars in the
US
run stock 13B 4-port motors? The only exception is the exhaust changes and a 48 mm side draft Weber Carburetor. The addition of the intake and exhaust will result in more efficient drivability and the fuel efficiently will greatly increase because of lessening the limitations of the air flow.
12A - The 12A engine is commonly found in early-mid RX-7s, which there is two distinctly different versions. One that fits to the Series 1 and another fits to the Series 2/3. The Series 1 motor has smaller runners and ports compared to the later versions. These entry-level engines were good for approximately 130 hp in their stock form - but it's not difficult to improve this.
12A turbo - As fitted to the Japanese market Mazda RX-7 and Cosmo, this motor was able to output 165hp. Being equipped with a turbocharger, the standard porting of this engine is quite different to the atmo version.
13B 4 Port - This is an early-model motor that was discontinued in 1986 for the 13B 6 port. This port setup produced up to around 140hp at its best. But because of its solid construction its an ideal platform to build up a high power race engine. There is a tremendous amount of material that can be removed to increase flow.
  13B 6 Port – This setup was released around 1986; the Series 4 RX-7 6 Port engine made 160hp and used an extra set of staged ports to aid breathing. Triggered by exhaust backpressure, a rotary sleeve opens the secondary ports up to allow more gas to pass. This system served to deliver good bottom end torque combined with top end power. Unfortunately there isn't much more that can be done to these port designs to gain more power.
13B turbo - Another 4 port design, this force inducted engine came with a factory air-to-air intercooler to produce up to 200hp. It uses larger ports and runners than the atmo 13B 4 port and by removing its stock EFI hardware and replacing it with a carb makes an effective and easy upgrade over a 12A or early 13B. With this conversion, around 134 rear wheel horse power is possible (with a conventional street exhaust). Although if you keep the EFI set up you would probably gain more power on top of that figure. The latest twin-turbo Series 6 RX7 versions have even larger ports and runners again, which are built up from all-new end plates which are non-interchangeable.
 The beginning of a great engine port begins here with the standard port. This is the port that will be modified to a mild, extended, bridge port, etc. If you desire to make your rotary engine faster you’ll want to start porting and polishing.
PRO'S: Standard drivability and fuel efficiency
CON'S: Limited scope for power
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