13B and 20B RX-8s

Although a very well balanced car, the Mazda RX8 always lacked a little go in the horsepower department compared to the older RX-7 it replaced.

Peter’s 2009 GT spec street RX8 is a great example of tuner build done well. Rather than persist with the factory 13B 2-rotor Renesis engine the Promaz team has installed a 20B 3-rotor engine using a turbo race port. This wasn’t a case of just dropping it in and starting the key. Fitting the engine is a Promaz bolt in front engine cross member. There are also numerous billet CNC parts machined in house such as the oil pan, power steering and air con adapters.

Boost comes from a Garrett GTX42R turbo complete with a Tial exhaust housing that runs into a twin 3in exhaust system. Still running on regular pump unleaded fuel, this is aided via a Promaz methanol injection system incorporating a billet fuel rail. From the outside the car still remains stock but sits a touch lower thanks to BC coil-overs. A real pleasure to drive, the car is now so much more responsive not to mention that 3-rotor howl. Let’s check it out on the dyno!

2009 Mazda RX8 GT
20B rotary engine by Promaz
[ Promaz turbo race port ] Garrett GTX42R turbo @ 16psi
[ Tial exhaust housing ] Turbosmart wastegate & eBoost controller
MicroTech LT16 ECU, pump unleaded fuel
Promaz methanol injection
[ billet fuel rail ] 3.5in dump pipe, twin 3in exhaust
[ Magnaflow 3in stainless mufflers x 4 ] Promaz CNC billet throttle body flange, sump
steering, aircon & crank angle sensor adapters
Promaz bolt in cross member kit
Promaz custom radiator & intercooler kit
Exedy hyper single plate clutch, 2-way LSD diff
Mazda FD/RX8 custom gearbox with modified gearset

Here’s another late model Mazda using and older style rotary engine this time in the way of a 13B twin rotor Cosmo engine. The RE engine as found in the JC Cosmo is similar to that of the Series 6 RX-7 but features larger secondary ports.

Fitting the engine is a Promaz bolt-in cross member while the engine itself has been freshened to a turbo bridge port specification. The factory twin sequential turbochargers have made way for a single Garrett roller bearing unit mounted on a custom manifold with boost governed via a Turbosmart wastegate. A switch to E85 pump fuel has enabled an increase in boost, but as the stock RX8 gearbox is still in place we’ve opted to a more forgiving organic single plate clutch.

Mazda RX-8 
Promaz 13B-RE Cosmo turbo race bridge port engine
Promaz custom bolt-in cross member
Garrett roller bearing turbo charger
Turbosmart 50mm wastegate,
Turbosmart eBoost Street electronic boost controller
Promaz custom E85 fuel system with Bosch 044 pumps
Promaz custom inlet manifold, intercooler and piping
Promaz billet crank angle sensor adapter
Exedy heavy duty clutch with organic plate
Factory stock RX-8 gearbox
Simmons 22in gold plated wheels