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Six Shooter: Mazda RX-4

Meet the future of custom-built rotary engines

Brad Lord
Dec 18, 2013
Photographer: Alastair Ritchie

For something so simple in its make-up the Mazda rotary engine is remarkably versatile. Whether you’re talking 13B or 20B, naturally aspirated or force fed, it’s hard to beat the power per cube ratio that these compact little motors generate; which goes some way in explaining why legions of tuners the world over still worship its design more than 40 years after it first broke cover.

Mazda rx4 engine 01 Photo 2/44   |   Six Shooter: Mazda RX-4

Pulse Performance Race Engineering in New Zealand is one of the converted. Warren Overton, its owner, has been toying with rotary engines for more than a decade, and five years ago set up shop and started churning out scratch-built three and four-rotor packages. Now he can add six-rotor to that list—PPRE calls it the “6B.”

“When we came up with the idea for this engine I wanted to build a promotional vehicle [around it] to highlight the skill sets on display to future PPRE customers worldwide,” says Warren. “The owner—my good friend and long-time client Alex Sigley—has had the car since he was 13, and it was his first. It was important to start with an old school ride and this particular car had sentimental value to me in the fact it was the first rotary I ever drove when I was just 14 years old. Alex and I had a shared interest in the finished project so we proceeded to build the car of both our dreams.”

Mazda rx4 front 01 Photo 3/44   |   Six Shooter: Mazda RX-4

Right from the get-go the idea was to create a truly one-of-a-kind Mazda. “We wanted to keep the original exterior profile of the vehicle looking standard,” says Warren, “but with a tough Pro Street stance to match the power plant.”

Looking at the finished product, it’s hard to argue that they didn’t achieve what they set out to. The RX-4 has never enjoyed the same popularity as its R100, RX-2 and RX-3 siblings, but in this scenario its attitude pulls off a look normally only reserved for V8 muscle cars with ease. The custom-concocted Midnight Blue Pearl paint that’s been laid over the coupe’s perfect steel panels helps the cause, too.

Mazda rx4 seats Photo 4/44   |   Six Shooter: Mazda RX-4

Like the bespoke three- and four-rotor engines the company has gained a worldwide reputation for—thanks in part to the exploits of Red Bull-sponsored Kiwi drifter “Mad Mike” Whiddett and his quad-power RX-7—the 3.9L 6B utilizes a mix of custom tooled or modified parts, as well as off-the-shelf Mazda rotary engine components. “The trick to building the engine lies within finding a solution on how to physically assemble the components together in the correct order,” says Warren. “Coming up with the design for the first custom four-rotor engine certainly helped me find a way to achieve this new goal.”

Mazda rx4 start button Photo 5/44   |   Six Shooter: Mazda RX-4

At its heart is a handcrafted PPRE five-piece eccentric shaft that features a special mechanism designed to support it within factory 13B engine plates. Six FC3S series four RX-7 rotor housings are utilized and fitted out with RX-8 13B-MSP Renesis rotors equipped with PPRE apex seals. On the intake side of the engine a six-deep row of PPRE/EFI Hardware throttle bodies with open trumpets sit on a custom tapered intake manifold. Fuel is supplied through one dozen 550cc injectors supplied from a pair of Bosch Motorsport 044 pumps, and given the squeeze via a Malpassi adjustable fuel pressure regulator. Then there’s the spark, where 12 Bosch Tec coils are used in conjunction with two MicroTech X6 ignitor modules. The setup is much more simple on the exhaust side—a custom fabricated 1.75-inch diameter tubular header running six branches into two, into one single un-muffled pipe that exits just ahead of the rear tire on the passenger side.

It’s angry and very loud. It’s also very powerful, having spat out 813whp on PPRE’s rolling road after tuning through a heavily modified MicroTech LT-16C engine management system. Then there’s the rear-wheel-measured torque curve, which according to Warren starts early with remarkable throttle response, and peaks at 650lb-ft thanks mostly to the engine firing every 60 degrees of rotation.

Mazda rx4 belly Photo 6/44   |   Bet Mazda's engineers never imagined this would happen... but we're positive they don't mind!

Building the 6B was one thing, but fitting it in the Mazda threw up a whole new set of challenges in itself. Given that the RX-4 was only ever designed for a two-rotor engine, modifications had to be made to the firewall and the transmission tunnel to allow the necessary room, but it still came at the expense of a conventional cooling system. “With the shortage of space in the engine bay, the longer engine setup didn’t allow much of a radiator in the usual place,” says Warren. “So we had to plumb two additional radiators into the boot, reticulated via a rear mounted electric pump system. This works fine for street use but we plan to set up an extraction system to build in some additional cooling capacity.”

Mazda rx4 trunk 01 Photo 7/44   |   Six Shooter: Mazda RX-4

Although the car was built primarily for the street, Alex and Warren didn’t mess about when it came to piecing together a driveline system. Hanging off the back of the engine is a Tremec 600 five-speed manual gearbox with a Tilton triple-plate clutch and a custom PPRE flywheel. Through a PPRE-engineered driveshaft, a Moser nine-inch rear end and 35-spline axles put the power to the ground. The suspension setup is custom-modified for the application too, with QA1 coil-overs holding up the custom four-link arrangement in the rear, and Koni inserts at the front. Combined with the large rear wheel tubs, which allow the Mickey Thompson-wrapped Weld AlumaStar alloys to sit well up into the body, there’s a four-inch ride height drop. Wilwood brakes feature at all corners, with a rear panel-mounted parachute for race day.

As it stands right now the 12-month build has around $100K sunk into it, with the largest slice of the investment channeled toward that motor. But it’s not finished just yet. The floor pan on the passenger side of the car has been cut and lifted to allow room for enough mufflers to cut exhaust noise output to a more respectable level, at which point the RX-4 will have ticked all the engineering boxes and be 100 percent legal for use on the road in New Zealand. That said, when the rear inner fenders were under the knife, Alex and Warren made sure there was plenty of extra clearance to allow them to run much wider tires than the 15-inch Mickey Thompsons currently fitted and take it to the drag strip—hence the ‘chute. Given the horsepower the engine is outputting—around 1000hp at the flywheel—and the way the chassis and suspension modification have transferred the weight and helped it to hook up in testing, Warren makes no bones about its eight-second strip potential.

SSTP 140100 OLDS 10 Photo 8/44   |   Six Shooter: Mazda RX-4

As far as the future of the PPRE 6B engine is concerned, Warren has clear intentions. “We’ll certainly look at doing some form of forced induction at some point. I have no reason to question the design’s strength, as there’s really nothing different here to our four-rotor, and we’ve been turbocharging those motors reliably for some time, including a 1300hp setup in a jet boat. But before we head down the turbo route we’ll probably get an animal like [Mad] Mike [Whiddett] to put it through its paces and prove its reliability in naturally aspirated form...”

The build has already attracted the attention of Mazda USA, which has pledged to lend any technical support to this ongoing project, should PPRE require it, which is pretty cool. For now though, Alex and Warren can be safe in knowing that what they’ve created in a little country at the bottom of the world isn’t just a world-first, but one of the wildest rotary-powered machines in the history of the engine itself.

Mazda rx4 guages Photo 9/44   |   Six Shooter: Mazda RX-4

Tuning Menu
Mazda RX-4

Owner Alex Sigley

Hometown Wanganui, New Zealand

Occupation Builder

Power 813whp

Engine PPRE 5-piece eccentric shaft, custom peripheral porting, apex seals, modified stationary gears and tapered intake; Mazda 13B FC3S S4 rotor housings; 13B-MSP Renesis rotors; PPRE/EFI Hardware throttle bodies; 6-2-1 header; 550cc injectors; dual Bosch 044 fuel pumps; Malpassi adjustable fuel pressure regulator; Bosch fuel filters; dual MicroTech X6 ignitor modules; Bosch Tec coils; three radiators; electric water pump; Peterson external oil pump

Drivetrain Tremec 600 5-speed gearbox; Tilton 7.5-inch triple-plate clutch; PPRE custom flywheel and driveshafts; Moser 35-spline axles and aluminum 9-inch diff with 4.1:1 final drive

Engine Management Custom-spec MicroTech LT-16C

Footwork & Chassis Coil-over modified strut casings, Koni dampers, 600lb springs (front), custom 4-link, QA1 adjustable coil-overs, custom PPRE sway bar (rear); custom rear wheel tubs; Tilton adjustable pedal box

Brakes Wilwood calipers, rear rotors and Street Performance pads (front/rear); Mazda FC3S S5 front rotors

Wheels & Tires 15x5.5" front, 15x12" rear Weld AlumnaStar wheels; Mickey Thompson tires

Exterior custom Midnight Blue Pearl paint; Auto-Gauge water temp, oil temp, oil pressure meters and parachute

Interior Six-point NZDRA-spec roll cage; STA seats; Sylvester 4-point harnesses; SAAS steering wheel; PPRE gear knob; Auto Meter Shift-Lite


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