NoPistons -Mazda Rx7 & Rx8 Rotary Forum

PAC MEN

Sydney, Australia, is very much alive with enthusiasm for Mazda's remarkable little rotary engine. Driving through the everyday bump-and-grind will reveal the odd brap-brapping PP RX-3 sliding through traffic, and come nightfall on a Friday or Saturday night and you'd better be into rotaries! Many of these Sydney-siders take these cars ultra-seriously!

None more so than the two proprietors of Pac Performance, as they pump so many of these hot cars out. Rocky and his brother George absolutely live and breathe rotaries, and are always pushing the pace of these cars to new heights. How do flat-to-low nine second quarters grab ya?

Rocky owns a '72 model RX-2 coupe, which is just capable of keeping brother George's pictured 4-door at bay - just! But what's really intriguing is that both these cars run significantly different engines - one a 13B twin rotor, the other a 20B triple.

With similar a mass, both cars must produce similar power given their relative quarter mile closeness, but George's larger capacity triple rotor is generally regarded to be the least stressed (or, rather, not quite as stressed!).

However, it's the 13B in the 2-door that comes up trumps in the power play. Built up from a Series 6 RX7 motor, it's been subjected to "mild turbo porting", doweling and a modified oiling system with revised galleries and increased circulation pressure. It spins a pair of lightened and balanced rotors wearing 3mm steel apex seals, and Rocky says it's so reliable it "can do 40-60 passes before it needs a freshening up". Its also been on their chassis dyno for a total of around ten hours - pulling a maximum of 650hp (calculated at the engine) at 8300rpm with a major 27 psi of encouragement. At a more sedate pace, the car's also been used for a couple of weddings and high-school formals. Imagine rolling up to a formal in this thing - that's one way to get noticed!

The 27 pounds boost (usually kept down to around 23 for the track) comes from a big T04 'S' turbo with an H-trim compressor wheel and various other increased flow mods. It's mounted on a custom tubular exhaust manifold with 2-inch diameter runners constructed from mild steel.

A Garrett 52mm external wastegate is also plumbed into the manifolding, and gets controlled by a HKS electronic boost control computer that enables easy changes to boost pressure.

Two-and-a-half inch pipes put the turbo'd air into a monstrous Hyperflow air-to-air intercooler measuring approximately 10x18x3 inches. As Rocky says, "Mate, it's large" - producing near-ambient intake temps at all times. After the intercooler, an RBR blow-off valve vents air when the throttle snaps closed. The Mazda single throttle body was enlarged slightly and bolted back onto the standard intake manifold, which has been match ported to maintain good flow.

Fully programmable engine management is fitted in the form of a Microtech MTX8 ECU. Controlling both fuel and ignition, the most has been extracted from this set-up though extensive chassis dyno tuning. The fuel system comprises two Bosch Motorsport pumps in parallel, a Malpassi regulator, twin 5/16-inch lines (plus a return), and a set of Rochester methanol injectors. The Microtech unit activating Bosch direct-fire coils, with Magnecore leads and NGK plugs takes care of the spark issue.

Tilton's twin-plate clutch manages the brunt of the 650hp, clamped by a heavy-duty pressure plate against a heavy-duty steel flywheel. A drag racing oriented Jerico 4-speed with straight-cut gears sits under the Mazda's trans hump, passing the torque on to a 9-inch diff via a custom 3-inch tailshaft. The diff uses 35-spine shortened axles and a 6.11:1 full-spool centre to pick the car up out of the hole. In fact, the car can jump the 60-foot line in 1.3 seconds and pull close to 2Gs on take-off - which slowly falls to around "only" 1G through the traps... 0-100 km/h comes up in approximately 2.1 seconds...

Seeeeeeya!

The 4-link rear end is a full custom fabrication by Mark Williams, which incorporates Spax adjustable coil-overs that Rocky says are set to suit each different track on the day. Pure traction comes from the 31-inch tall 14½ -inch Hoosier slicks that crumple up nicely when things get moving. These are worn on 15-inch diameter Weld Wheels front and rear, but the front runners are clad in skinny MT rubber. Vented and drilled Commodore discs are located at each end, working with VL Turbo front calipers and Series 2 RX7 rears.

A full 8-point steel cage, Velo seats and a 4-pont harness ensure safety within the cabin, while there are also some surprising touches of road-going comfort as well. Custom door trims and Racing Hart yellow wood-grain add a little something, while there is also a splash of Autometer gauges to view just about anything - except the time.

Rocky's brother George has gone the triple rotor route in his street reg (and driven!) RX3 sedan. Pulled from a Mazda Cosmo in Japan, the big 20B motor is the big-banger in the rotary family. With its extra rotor there's heaps more torque everywhere in the rev range, and it has the potential to produce equal power to the 13B but at lower revs and with less boost. At present it is slightly behind the 13B, but they have seen 440hp at-the-wheels already - good enough to push the car to a 9.11 second quarter at 147mph.

Pac have pulled the motor apart and fitted 3mm steel seals (as in the 2-door), a hi-volume oil pump and more of Pac's "mild turbo porting". The intake has been refitted with a RBR intake manifold featuring fatter diameter runners than the standard item to decrease intake congestion. To this, are bolted three magnificent 50mm throttle bodies produced by Injection Perfection.

Once again, a Microtech system (an MT12 this time) controls everything relating to fuel and ignition. No less than six 12A turbo injectors are pulsed, with fuel coming via two Bosch pumps together with a swirl pot arrangement and a Malpassi reg. Bosch direct fire ignition is used, channelling energy through Magnecore leads to a set of cool temperature NGKs.

The turbo is another T04 unit, but with different trim and specs to the coupe, and it regularly pumps 17 psi into the front mounted Performance Metalcraft intercooler. Again, this thing is huge enough to ensure intake temps are minimal. To fit the big T04, a custom tubular exhaust manifold was fabricated, also incorporating a 42mm Garrett 'gate to manage boost. A RBR blow-off valve is fitted to the intake.

The ever-strong Powerglide auto trans is bolted to the back of the heavy-duty steel flywheel in conjunction with a "bitsa brand" hybrid 4300rpm torque convertor. From this runs a 3-inch tailshaft to a 9-inch diff out the back with Strange 35-spline axles and a 4.86:1 full-spool centre. A similarly designed 4-link rear-end to the 2-door makes a home for Pedders adjustable rear coil-overs and Commodore discs and calipers, while at the front are vented Commodore discs bolted to the standard suspension system. These brakes are a huge increase in performance over standard - but then, they'd need to be.

Being a genuinely road driven vehicle, the interior is brought up to scratch with a full re-trim in grey velour, the extreme looking Velo race seat and a comprehensive array of gauges. And, of course, there is a 10-point safety cage to protect George's head. Both cars are covered in "Pacman Yellow" which is a custom mix, and there is prominent signage created by Nippy signs. George's car even extends to writing that says "Having Chev for breakfast, having Ford for lunch"!

BY MUZZA