Hi
I am new on the site, and new to rotaries; i would like to know how i can find out how ports has the rx7 i wanna get; it will be either a 12a or a 13 b ( without taking apart the engine) thanks

 

Welcome to the board.

When we refer to port numbers, we are referring to the intake ports. Just locate the intake manifold and look at it. The 4-port engines will have fairly simple manifolds while the 6-port engine manifold are bulky and busy (due to the overall length and auxiliary port actuators). No need to take them apart for that.

The 12A is going to likely be a 4 port engine, unless someone built it otherwise or imported a genuine 6 port from Japan.

The 13Bs can be either 4- or 6-port, depending on year and application.
- pre-Rx7 engine are 4 port
- Non-turbo Rx-7 engines are 6 port
- Turbo Rx-7 engines are 4 port

I'll just throw the MSP (Rx-8/Renesis) in here for the sake of completeness. They can be 4- or 6-port as well, but they are easily identified as they have 4 exhaust ports (though it looks like only 3) in the side housings whereas ALL previous 13Bs had two exhaust ports in the rotor housings themselves.

 

Thank you very much , i can now understand, i've seen it on the 13 b engine pics; an interestind debate is which is the best one; i've understood that the 4 ports is better if one wants more bhp, but the 6 has more power stock if i am correct

 

Yes, and no. 6-ports had more power than the old (70s) 4-ports, but that's really no big surprise when you compare how they came equipped. None of them were ever carbureted - instead they had somewhat complex and tuned intakes - and they all had at least 0.2 compression points more. When looking only at factory numbers, no 6-port has ever exceeded a factory turbo engine in output (hp or torque) - again, no surprise. They can be built and or tuned to do so, but likewise the 4-port turbos can be built and tuned as well, so that's kinda moot. When it comes to building and tuning as N/A engines, the 4-ports eventually do edge out the 6-ports with streetporting, but when it comes to bridgeporting, the 4-ports have a bigger advantage there. Also keep in mind that rotating assemblies got lighter with time so more power was pretty much a given with each evolution.

For Renesis engines, the simple answer is 6-ports are more powerful.