Corey Armstrong's triple rotor Turbonetics-forced and Indy-intercooled drag rail is simply awesome. With over 600hp available, the sound of the 3-rotor motor creates more than a second glance when it disappears off down the track!
Corey Armstrong has a serious need for speed. Only a short while ago, his awesome drag rail was powered by a full-house Nissan FJ20 turbo that had proven good for a 10.1 second quarter mile pass at over 136mph. But the desire to dramatically slash that already-impressive ET and to run a car totally different to any other rail in the country proved overwhelming. The solution turned out to be an ex-Mazda Cosmo triple-rotor turbo engine. And it's panning out to be a good choice, as Corey says he's aiming for the car to now be running in the low 8-second bracket with this new motor - once everything has been fully sorted and is running sweet.
The 3-rotor motor in its current modified form is good for over 600hp and really shows its torque advantage over the twin-rotor 13Bs, as this sucker grunts hard. It was the rotor-experienced Shaun Gibbs that rebuilt the engine to its performance specs, using the standard Mazda rotors cut to accept 3mm RX-4 type steel apex seals. These seals were chosen because they have proved very reliable in the past, and it isn't intended that a heap of boost will be forced into the combustion chambers. The housings have been carefully massaged for extra flow with a mild extend-port job that isn't quite as radical as the RPM workshop say they'd use on a normally aspirated engine. The standard (but already big) Mazda through-bolts are retained as these are also very durable. But it was discovered that to fit the engine to the chassis, a custom alloy sump was needed to achieve the desired amount of ground clearance.
To ensure the longevity of the engine, there's an ex-motorcylce engine radiator mounted at the rear of the car, a Series 3 RX-7 oil cooler and a trans cooler with quality braided lines used extensively.
The turbo side of things is extremely impressive. A custom exhaust manifold was made up from 2¼ inch mandrel bent pipe that leads into a small chamber just before the single pulse turbine entry to the turbo. Drawing through a large K&N filter, this is a unit of "secret specs", but we can reveal that it is a Turbonetics T76 with a free-spinning ball bearing centre. A 42mm Racegate tee'd out from the exhaust manifold controls boost pressures of up to 15psi, and it uses the standard valve body and internal spring pressures in its operation.
The compressed air makes its way through 3-inch mandrel plumbing into a 3½ inch thick air-to-air intercooler being fed air by a large scoop on top of the engine. This core is the same design as the Indy Cars use, and it contains a highly efficient finned internal design. To vouch for its performance, Tim of RPM says he's never seen air temperatures any higher than 36 degrees Celsius post intercooler. More 3-inch mandrel bent plumbing and heavy-duty hose clamps then connect to the exit of the 'cooler and lead to the mouth of the standard-but-sophisticated 20B throttle body. And because the standard intake manifold appears to flow quite well, this was left in place.
Engine management is via a fully programmable Microtech MT-12 ECU that is amongst the very latest series. This is wired up to fire six 12A turbo injectors and a line of six Bosch high-energy ignition coils hidden under the intake manifold. The rev limiter has been set at a relatively conservative 8250 rpm, which really emphasises the point that this is one high-torque engine. Quenching the engine's mighty thirst for methanol is a pair of Bosch Motorsport fuel pumps plumbed in parallel, with the correct rail (uh oh, pun alert!) pressure maintained by a Malpassi rising rate regulator. A small alloy fuel tank located behind the driver's seat stores the minimal amount of fuel required.
Squashed up behind the standard flywheel is a faithful ol' 2 speed Powerglide auto trans and a 7½ inch stall converter mated within a custom bell housing. The fabrication of the bell housing also allowed the necessary relocation of the starter motor. While we were compiling the story, the stall rpm was still being discussed as the 6000 rpm unit from the previous engine was proving to be too high. Shifts are made by an air-shifter set-up that gets controlled by the clever Microtech computer, while there is also a trans brake fitted that holds the engine under load at the starting line, giving extra strong launches.
Torque is then passed through a heavy-duty yoke directly to the differential, so no losses are made through a clumsy tailshaft. An ever-reliable 9-inch diff is fitted, using a Strange full-spool 4.11:1 centre and Strange 31-spline axles. And in case you couldn't tell, these are very, very short to accommodate the big rear slicks. Namely, these are 12 x 30 inch Goodyears worn on Weld Illumistar rims, while at the front are the somewhat superfluous Michelin motorcycle tyres on wire-style wheels.
The chassis itself has been home to a wide variety of engines. Initially, the vehicle was built to accommodate an all-alloy Toyota V8, then a 350 Chev, followed by the FJ20 and 20B turbo motors. A bloke called Doug Dickenson constructed the homemade frame in tubular steel, giving it a wheelbase of 170-inches for maximum straight-line stability. The engine and trans have both been hard-mounted to the chassis but are in no way stressed members of the overall chassis. Extensive bracing across the diff and rear axle housings came fitted when purchased from the previous owner.
Steering is thanks to a LX Holden Torana rack and pinion set, linked to a basic front wishbone suspension design.
There aren't any front brakes to be found at the hub of the front suspension, but rest assured that relatively large VB Commodore rear discs clamped by a pair of Girlock Mitsubishi Sigma calipers have a large impact on retardation. And so does the sizeable Deist parachute that hits hard when it's deployed.
Corey sits nice an' snug in the cockpit, crammed with controls for the rear 'chute, auto trans brake, air shifter and also a throttle-stop solenoid that enables 100% consistent launch rpm.
Once the show gets moving, gearshifts are performed at about 7000 rpm to keep within the engine's peak power band. There's also a VDO tachometer, RPM harness, competition style bucket seat and a side-handle steering wheel to take up any vacant space.
All up, the car weighs around 1450 pounds (659kg) with Corey in the driver's seat - which is pretty light for a steel chassis'd rail. And the 600-plus horsepower combined with strong torque through the rev range means this is one force to be reckoned with - just ask the competition! There's now a growing line of people with a newfound respect for the mighty Mazda triple rotor...
The rail ran the stunning 8.4 second pass just before this issue closed. Next week we'll give you the full details in our Performance News section.
Contact:
RPM Performance Centre
+61 8 82772266
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