The 3rd generation (FD) Mazda RX-7 is one of the best driver’s cars to ever come out of Japan. Unfortunately, its turbocharged rotary engine has a bad reputation for being unreliable, and it’s pretty common to see them swapped out for V8s. The rotary is just too awesome to give up on, and it’s not difficult to make a lot of power out of them. However, most modified RX-7s do not have the fundamentals in place to keep them cool and prevent them from blowing up. This project will show you how to make a rotary reliable and highly capable with the right approach, proper engineering, and modern technology.
There’s something quite special about the “FD3S” RX-7. Its lightweight engine and chassis give it a 50/50 weight distribution, it has a double-wishbone suspension front and rear, and its driving dynamics could be considered a benchmark for any sports car of any generation. The “FD” is a true “driver’s car” in every sense. Think of it as a 7% larger Miata that’s stiffer (being a coupe) and has over twice the power and torque.
I’ve always been a fan of rotaries and thought the FD RX-7 is one of the best looking JDM cars from the 90’s. When I was approached with the opportunity to consult on the build of a FD RX-7 to a modernized OEM+ level, I was excited to be part of it since I actually got my start racing cars in time attack competitions driving a 1972 Datsun 510 powered by a turbocharged 13B rotary engine.
My background racing cars professionally and as a development driver for programs such as the LeMans-winning Ford GT race car, the Ford GT road car, Shelby GT350 and GT500 Mustangs, among many others; I have a lot of OEM and motorsports contacts and suppliers that can help solve the inherent issues of the rotary engine, and to advance the RX-7 platform. Since I grew up around people who built and raced rotary engines for decades, I have a lot of expertise to lean on.
We will dive into the details in future articles, but the biggest challenge of the rotary engine is keeping it cool, which has been poorly addressed by most products on the market. We will show how to properly cool these engines and develop some products along the way.
The RX-7 uses one of the most unique internal combustion engines ever used in a car, the 1.3L turbocharged “13B-REW” rotary engine, designed by German Felix Wankel in 1929. This engine delivers insanely smooth thrust in a very power-dense package. This engine works essentially like a 2-stroke and has very few moving parts; with no pistons, connecting rods, valves, valve springs, or camshafts. The main rotating components are the rotor and the eccentric shaft (crank shaft).
In fact, the rotors themselves spin at 1/3 the speed of the eccentric shaft. So, when the rotary is spinning to its 8,000rpm redline; the rotors are actually only spinning at 2,667rpm. In other words, for the rotor to make a complete revolution, the crank makes 3 full revolutions (or 1080*). Each rotor has a displacement of 650cc’s, so the two rotors together total 1,300cc or 1.3L.
A normal 4-stroke internal combustion engine has a power stroke every 720* of crankshaft rotation (2 full turns) per piston, while a 2-stroke has a power stroke every 360*. The rotary is considered a 2-stroke because it has a power stroke every full revolution of the crankshaft (per rotor face), and since it does not have valves or camshafts with the intake and exhaust port shape determining the engine’s timing. This makes its 1.3L of displacement more comparable to a 2.6L four-cylinder engine.