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Roadwood: rough-and-ready 20B HQ

28 February 2018



An HQ in NZPC? No, we haven’t lost our minds

You’re probably sitting there wondering what the hell a not-so-polished Holden HQ is doing in in the pages of NZPC, right? The look on your face right now is probably very similar to that of everyone at this year’s Chrome Expression Session when said HQ blasted past, leaving that distinct 20B note in the air. It was undoubtedly one of the most talked-about cars of the event, with everyone asking the same damn question, what the actual f#ck?! 

To be fair, the idea of a rotary-powered Kingi is nothing new — it’s something the Japanese actually produced in the 1970s, purchasing HJ and HX Premier shells from Holden and then dropping 13Bs in-between the struts, and calling them Roadpacers. 

Although the name suggested some kind of speed machine, the naturally aspirated 13B’s lack of torque made the Roadpacer a sluggish car that failed to hit the mark with Japanese luxury sedan buyers, and only 800 units ever moved off Mazda showroom floors. Such low sale figures made the Roadpacer one of the rarest Mazdas, up there with the 110 Cosmo, and it’s a car that people tend to rubbish on a regular basis. But there are those who looked at the concept and thought yes, that could work. Add a little more capacity and a touch of boost, and the Roadpacer could have been the best damn sedan to hit the market in the ’70s — if only the 20B had been available to Mazda engineers at the time. 

“It’s actually a really great cruiser, boost doesn’t kick in till 4000rpm”



When we say ‘those’, what we actually mean is one man, a Taranaki hoon by the name of Andrew Perrett, who after 19 years of giving his two-owner HQ an absolute hiding — and 16 diffs, two gearboxes, three engines and seven driving convictions — hatched a plan with good mate Hayden in the early 2000s. They reckoned they could right Mazda’s wrong, and show that a Roadpacer could, should, and would work. “We were working on it one night changing the plugs, as the 202 always fouled them, when Hayden looked at it and said “Farrrr, a 20B would fit in here.” Andrew continues, “We weighed the HQ one night with a coma’d chick in the back seat, subtracting her 60kg it came in at 1400kg, that’s lighter than the Cosmo.”

Six months later a Cosmo 20B front cut was in the shed next to the HQ, the motor was swapped over, and the twin turbos were ditched in favour of a custom manifold with a big single Master Power GT45. Now, looking at the car you might wrongly assume Andrew to be some kind of automotive butcher, but the reality is, he’s far from it. He wanted to avoid chopping the tunnel as much as possible to keep the charm that only a Holden benchy would deliver. To do so it took a couple of attempts at fitting the engine, but the second time around they nailed it, and that meant the benchy could remain. Six-up boost runs, anyone? 

Fifty shades of gold, the HQ’s looks have never been a priority, and never will be



Like all good projects, a few curveballs were thrown in along the way, the worst of which was the internal wiring in the MicroTech actually being fu#ked up, causing all manner of head-scratching issues that would stretch out over a year, as they tried to get to the bottom of it. Eventually they diagnosed the issue, and were able to wire the car around the problem. Once that was sorted it was on the dyno, throwing down 309kW (415hp) to the rear Cooper Cobra rubber. It was time to see if a rotary-powered HQ would actually be as slow as the world seemed to think. 

“When me and a mate took it down the road and hit boost for the first time we just cracked up, I got home that night and thought shit, I don’t need a car this fast,” Andrew recalls. But now the novelty of that boost hit has subsided somewhat, you can expect the HQ to continue to improve, again via Andrew’s style of not butchering things along the way. The 20B — which the boys had refreshed with new SCR seals — has matching-numbers block, so instead of taking the die grinder to those sought-after plates, some semi PP housing will eventually make its way into the lineup, but that’s a long time down the track, and for now he’s content with confusing the uneducated into thinking it’s a six pot engine. “Everyone expects a rotary to go brap brap.” But there is also a serious[ish] side as Andrew explains; “The whole car is an experiment, I really want to see how much power we can make on the stock ports before we worry about modifying the motor.” 

As you can imagine, the HQ is a pretty polarizing car. People either ignore it due to its roughness, become disgusted it’s powered by some ‘Jap crap’, or are totally blown away and truly intrigued by the transplant, and that’s old V8 devotees included. Not that stirring any kind of reaction from anyone is, or was ever Andrew’s aim, it’s always just been about having fun, and 19 years on from that first burnout, it’s still delivering that fun more than ever before. 

1972 Holden HQ ‘Roadwood’

ENGINE: Mazda 20B, 2000cc, triple rotor
BLOCK: SCR apex seals, S5 exhaust sleeves
INTAKE: Nissan GT-R intercooler, modified throttle body, Trundle special air filter
EXHAUST: Four-inch downpipe, twin 2.5-inch pipes, twin Manawatu custom mufflers
TURBO: Master Power GT45, AVP custom manifold
WASTEGATE: Turbosmart 60mm
FUEL: Deatschwerks DW350 pump, Holley Blue lift pump, surge tank, -8 sparkle lines, Injector Dynamics ID1000 injectors, Malpassi fuel-pressure regulator
IGNITION: Bosch coils, MSD leads
ECU: MicroTech LTX12
COOLING: Fenix BA Falcon radiator, AU Falcon fan shroud, Cosmo oil cooler with cold air scoops
EXTRA: Turbosmart eBoost, enlarged transmission tunnel, custom engine mounts

GEARBOX: FD RX-7 five-speed gearbox
CLUTCH: Modified heavy duty FD RX-7 clutch
FLYWHEEL: Lightened
DIFF: Ford nine-inch, Eaton Truetrac LSD (4.11), 28-spline axles 

STRUTS: Suspension Tech–built Bilsteins, King Springs
BRAKES: (F) Alloy HZ calipers, redrilled 5×114.3 rotors (R) Factory 229mm drums
EXTRA: McDonald Bros Racing adjustable upper trailing arms, 24mm front sway bar

WHEELS: 14×7-inch CSA Globe-style
TYRES: Cooper Cobra

PAINT: Original sunburnt gold, some rattle can Sunburst Gold, patina gold, and Success Gold, rattle can black
ENHANCEMENTS: ’68 Camaro lip, custom graphics 

SEATS: Recovered front bench seat by Customline Upholstery
INSTRUMENTATION: Reconditioned GTS gauges by Auto Instrument Services 

POWER: 309kW (415hp)
FUEL: 95 octane 

Andrew Perrett 
AGE: 37
LOCATION: Stratford
BUILD TIME: 15 years
THANKS: My viking Mrs Dagny for not understanding, but putting up with my weekends and late nights on the car and not the house, Ari and Louie the sausage for keeping dad company, Jason and Fiona for keeping it moving and feeding me, David at Stratford Auto electrical, Geartech for sorting the diff head, Trundles for letting us work late into the night sorting engine management issues, Marty for certs, the boys Chris, Nick, Glen, Wayne and anyone else I used to run ideas past and get me out of holes, Hayden for planting the seed, providing the brains, and expensive suggestions


This article originally appeared in NZ Performance Car issue No. 253 — you can get your grubby mitts on a copy by clicking the cover below