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Speed thrills: Andy Duffin’s FD RX-7

4 November 2014


Published in NZ Performance Car Issue No. 214

The thrill of speed is something that few other activities on earth can come close to matching. It gets under your skin and in your blood, and once there, it’s notoriously hard to shake. Even someone who has been out of the driving seat for 50 years will still have that twinkle in their eye when recalling those moments behind the wheel with their right foot planted. It’s an addiction plain and simple, and like most other addictions, it’s a hard thing to cure. The faster you go, the faster you’ll strive to go.

Andy Duffin, a circuit racer from Pukekohe, would be a great candidate as a poster boy for a speed-addiction clinic. He has raced rotaries since the 1980s, and last time we featured his FD RX-7 it had just been crowned SS2000 champion for the 2012–2013 season. Andy was running one bad-arse 216kW 12A PP, backed by an Elite Racing six-speed sequential. The car was no chequebook-produced rolling parts catalogue, but rather a cleverly-engineered chassis, with the right pieces in the right places. And although the small-capacity 12A lacked the straight-line speed shown by the bigger-capacity competition, it had great cornering characteristics. Just watch any of Andy’s in-car videos on You Tube to see what the definition of late braking is.

The combination was enough to take the overall SS2000 championship in 2012–2013, and set a few SS2000 lap records along the way. But having reached the top of that ladder, it was now time to move on to new challenges. GTRNZ’s GT2 class was chosen, and the goal was to be at the pointy end of the field, nipping at the ankles of the GT1 cars. It was now a question of what to replace the 12A with, as Andy explains. “I had always wanted a 20B FD after watching Mark Porter race his at Pukekohe in the ’90s.” But the team was very aware that stepping up engine output (and weight) could ruin the car’s handling charastics. “We thought a 20B turbo would be too hard on the rest of the car, the suspension, brakes and driveline. We didn’t want to have to re-engineer everything and mess up the essence of the car, as it worked well, we just wanted a little more power.”

So the engine is based on a factory 20B, and uses Series 5 RX-7 housings, with similar peripheral porting to Andy’s 12A, and high-compression NA Series 5 rotors which have been lightened, while the entire rotating assembly has been blueprinted to handle 10,000pm and beyond. To get to those revs up as fast as possible, the rotational mass has also been kept to the bare minimum, with a lightweight rotating assembly, and a 140mm twin-plate Quarter Master clutch, with an ultra-light chromoly flywheel.

All this, combined with the porting design, has meant the tacho can’t keep up when free-revving the engine. On the dyno it produced 362kW (485hp) at 10,000rpm, although it wants to rev past this point. The 12A was restricted under SS2000 rules, but the GTRNZ regs are much more free, and allow a considerably bigger intake. EFI Hardware supplied a triple 55mm Pro Race throttle-body kit, with six 1000cc injectors to feed in buckets of Gull 98, while perhaps the most dominating feature of the engine bay is the large air dam and intake, built in-house at Green Brothers Racing.

One thing that was a real concern throughout the build was the added weight, and where it would sit in the chassis. A Mazdaspeed dry sump allowed the engine to sit really low, and as far back as the firewall would allow. Weight was also removed from wherever it could be, with a mass of steel taken from the rear quarters. Mike Shaw Fibreglass supplied fibreglass doors, a rear hatch, and front and rear guards pulled from the moulds of the ’90s RX-7 guards that inspired Andy — those from Mark Porter’s FD — and Lexan was used on all the windows, including the front screen. At 1090kg, the new race-ready weight tipped the scales at only 40kg over the 12A.

Like most projects this one snowballed somewhat, and the entire car ended up being rewired by Te Rapa Automotive to accommodate the new Link G4+ Xtreme ECU, and extra sensors to log and monitor the 20B and driveline. Everything from the intake, gearbox, oil and water pressure through to the diff, gearbox, intake, water and oil temps are now logged. The amount of data pulled from the car is crazy, and allows the team to make sure everything is running as it should be.

The project ended up taking 12 months to complete, but hit a slight roadblock earlier this year. Andy’s addiction to speed saw him take the opportunity to compete in GT2 during the ITM 500 V8 Supercar round at Pukekohe, driving a friend’s S15. But things didn’t go so well — a mechanical failure sent the S15 into the Armco at the end of pit straight very, very hard! The seat broke on the second impact and Andy was pretty messed up, spending a stint in hospital with multiple broken bones and ribs, though he was a very lucky man to come away with only the injuries he did.

This wasn’t about to slow him down too much, and as soon as he was well enough to move around, he began piecing the car back together. “Even when I was in hospital I never thought about stopping racing, I knew I would have to get back in the car, and then if I decided it wasn’t for me, at least I had tried, I couldn’t go the rest of my life wondering.”

Only a few months later, and with one hand in a sling, Andy and his team completed the paintwork. He had already resprayed the majority of the shell over the Xmas break, with only the exterior to take care of, and just had to live through a few weeks of frustration to get all the final touches sorted.

We got the call from Andy to come and see the car during its shakedown runs at Hampton Downs on a cold winter morning, and it didn’t take us long to work out which pit garage they were in, as the very loud, angry bark of a 20B could be heard throughout the facility.

The FD has two muffler set-ups, both with custom Adrenalin R mufflers, the one we heard and another, much more restrictive and quiet option for tracks with noise problems, like Pukekohe.

A quick warm-up, a change of plugs and Andy strapped himself in, the first time since the crash at Puke, and still nursing a few healing injuries. On the dyno the 20B was revved happily to 10,000rpm, but today the rev limit was set at 8500rpm. Even then, the sound echoed down the front straight like an old F1 car as he banged up and down gears in the Elite Racing six-speed sequential. The RX-7 makes nearly double the power the 12A did, but the real question was, how did it feel from the driving seat? “It felt great, not too different to drive, apart from the extra power. Sure the balance had changed a little bit, but it didn’t take long to feel at home, it was like getting back into an old suit. I can’t wait to strap on some new, wider rubber with the wider 18s, and get a decent crack at it.”

It may have taken a little longer than first anticipated, as Andy missed out a season, but the car is now ready months ahead of the next GTRNZ series, and he is ready to go. Well, he will be by then. With an extra 149kW, an additional 30mm of rubber on each corner, and with weight and balance very similar to what it was before, this will be one hell of a weapon, able to take it to the big-budget teams, and Andy hasn’t even begun to develop an aero package. “We decided to leave the aero until after the car was going. At the moment it’s basically stock, with only a large front undertray. It’s always good to have something to play around with and develop.”

We will keep an eye on Andy and the 3 Rotor Racing team this season to see how they fare. But in the meantime we strongly suggest you go to our You Tube account and listen to this thing scream around Hampton Downs — you won’t be disappointed.

Tuning menu

Make and model: 1996 Mazda RX-7 (FD3S)


Engine: Mazda 20B, three rotor, 2000cc
Block: Mazda Cosmo plates, Cosmo 20B crank, Series 5 RX-7 housings, Series 5 RX-7 NA rotors, peripheral porting, lightened and balanced rotating assembly, blueprinted internals, Mazdaspeed dry sump front cover
Intake: EFI 55mm Hardware Pro Race throttle body kit, custom alloy airbox
Exhaust: Three-into-one mild-steel headers, Adrenalin R custom muffler
Fuel: 1000cc injectors, Bosch 044 main pump, SX fuel reg, Holley lift pump
Ignition: Mercury Marine coils, Magnecor plug leads, NGK race plugs
ECU: Link G4+ Xtreme
Cooling: Griffin double-pass radiator, custom-made oil coolers, Mocal gearbox cooler
Extra: Full rewire by Chris McDell at Te Rapa Automotive, engine and gearbox breather tanks, side-mount alternator mount, solid-mounted engine and gearbox


Gearbox: Elite six-speed sequential
Clutch: Quarter Master twin-plate
Flywheel: Lightweight race flywheel
Diff: Mazdaspeed LSD diff centre


Struts: Koni single adjustable shocks, King springs
Brakes: (F) Factory four-pot calipers, AP Racing floating rotors, Hawk Blue pads (R) factory calipers, AP Racing rotors, Hawk Blue pads
Extra: Green Brothers strut brace, Hardrace rear traction arms, Hardrace rear toe arms, Green Brothers steering arms


Wheels: 18×10-inch Enkei RPF1
Tyres: (Dry) 270x650x18 Michelin slicks, (wet) 270x650x18 Michelin slicks


Paint: 2K gloss black, sprayed by Andy
Enhancements: Mike Shaw Fibreglass rear quarters, front guards, doors, hatch, Mazdaspeed front bumper, polycarbonate windows, graphics by Head Case Designs


Seats: Racetech 4119HR
Steering wheel: Suede
Instrumentation: Auto Meter tacho, shift light, oil pressure, oil temp, water temp, warning light, Elite Racing Transmission gear indicator, Rollcentre lap timer
Power: 362kW (485hp) at the wheels

Useless fact

GTRNZ is home to some of the country’s fastest tin-top race cars. It’s split into three categories, GT1, GT2 and NZGT, and the cars are placed in their division according to their lap times. If you break out of your chosen class’ minimum lap time for that track more than three times during an event, or six times across a number of races and tracks, you will be shifted up a class.

GT1 Pukekohe 1min 6.999 and under, Hampton Downs 1min 8.299 and under, Taupo 1min 33.199 and under, and Manfeild: 1min 9.999 and under. GT2 Pukekohe 1min 7.0 and over, Hampton Downs 1min 8.3 and over, Taupo 1min 33.2 and over, and Manfeild 1min 10.0 and over. NZGT Pukekohe 1min 11.6 and over, Hampton Downs 1min 12.9 and over, Taupo 1min 39.45 and over, and Manfeild 1min 14.3 and over.