Words: Todd Wylie Photos: Deven Solanki
The Holden HQ is to Aussie and New Zealand car enthusiasts what Vegemite is to breakfast spreads — an Australasian treasure, a car that many of us remember our father or grandfather owning, usually in 202ci six-cylinder form, driving to work, running errands around town, and towing a boat or caravan at the weekends.
Although considered a classic muscle car straight from the production line when purchased in V8 form (with just 275hp when the 350 Chev was factory-optioned), the HQ produced between 1971–1974 is an ideal candidate for modifications that make even the most stoic mechanic raise an eyebrow. From the outside to the inside, Justin Johnstone’s 1972 Holden HQ four-door is every inch a new millennium street machine. The basics of this build are the same as they’ve been for years — a classic ’70s Aussie muscle car with clean lines, an engine bay full of old-school blown grunt, and a stance that not only looks good but also ensures the car corners like it’s on train tracks.
The story of this build started when Justin spotted two HQs for sale one evening while trawling on Facebook Marketplace, one almost complete and the other a rolling shell. He didn’t really need another car — let alone two — to add to his growing collection of Aussie Ford, Holden, and Mopars and went to view the cars, originally intending to buy just one of them as he had always wanted an HQ in his shed. But as happens to many of us, the second one seemed to find its way onto a trailer heading for home as well. Leaving the next day for an Aussie trip, he hastily stored them at a mate’s place, and when he arrived back from holiday, he had devised a cunning plan.
The rolling shell was dropped off to Darryl Crack at Cracks Repairs workshop for panel and paint, giving Justin time to start looking for an engine and trans. It just so happened that a while earlier he had brought a Jaguar XJ6 complete with an LS1 installed, and had started to part it out. The obvious thing to do was keep the LS1 for himself, making the future for the HQ engine bay look like it was going to be modern and fuel-injected, until Roly from Probuilt Engines in Invercargill sent a message about an older supercharged 350 for sale. It was a bit of a mess but not a lot of money, so the decision was made to go the old-school route, sell the LS, and start rebuilding the 350 and blower.
The old 350 had run into problems with the balancer coming off, wrecking the front of the crank, but it just so happened that Probuilt had a Scat crank lying around waiting for a high HP build, giving Justin the enthusiasm to push ahead and work through the rest of the issues with the previous rebuild. They included pushrods that were wearing on the guide plates, piston bores that weren’t parallel, and several other problems. Rather than admit defeat and find another engine, Justin persevered and ordered up forged pistons, standard rods, ARP bolts, a custom-ground camshaft from Franklin Cam in Pukekohe, Johnson hydraulic lifters, Edelbrock pushrods and guide plates, and plenty of other necessary new parts. Before assembly, he had the internals balanced and some mild porting on the intake and exhaust ports to complete the block and heads on this tough engine.
Once the engine was rebuilt with all the new components needed, it was time to bolt the freshly polished Hampton 6-71 blower on top. Nothing was easy with the fitment, and Justin soon figured out that the drive pulleys had been spaced out too far, and new spacers and a tensioner set up had to be fabricated for it. Feeding the blower, running at 8 psi, are classic twin Holley 600 carburettors which were modified for the blower, and a high-volume mechanical pump and pressure regulator takes care of feeding in plenty of fossil fuel when needed. The final components under the hood of this tough build are a MSD 6-BTM Speedmaster distributor, MSD Blaster coil, and Streetfire leads. Diamond Joe stainless headers feeding into dual 2.5-inch exhaust mandrel bent exhaust systems take care of waste gases, and Flowmaster FX mufflers attempt to minimise scaring animals and small children. A Fenix alloy radiator complete with 14-inch fan and an external oil cooler for the trans makes sure nothing gets into the red temp zone.
We are spoiled for choices of high-performance transmissions in New Zealand at the moment, but it was difficult for Justin to turn down a classic TH400 and converter from a mate for a measly $700. It was a bit soggy in the shifts initially, so Justin brought a B&M shift kit from eBay and upgraded the flexplate to a heavy-duty one, as it was struggling with the torque of the blown engine. With a Quicksilver shifter providing manual shifting options in the cabin, he’s happy to report the trans is still going strong after a few years of hard acceleration and many tyre-blazing amusement sessions—on closed roads, of course.
The final component of the drivetrain that needed toughening up was the Salisbury 3.08:1 factory diff, which only lasted about three weeks with Justin’s heavy foot. An 8-inch Ford diff with a TruTrac centre and 3.0:1 ratio was sourced from Charlton Imports in Gore, a jig made up, and the Salisbury mounts were transferred across, along with some mounts from a donor banjo diff that was lying in the back of Justin’s workshop.
Out the front, the stopping duties are easily handled by factory HQ front rotors and callipers, and the rear sports Falcon XR rear drums. The factory HQ suspension is actually really decent, so all that was required was Monroe GT gas shocks on each corner, a 27mm Whiteline sway bar, and Superlow front and rear springs with the rear reset 40mm closer to the asphalt. US mags Rambler 17×8-inch on each corner are a modern touch to this classic shape, and with front 235/45/R17 and rear 255/40/R17 tyres, they give just the right amount of grip to provide plenty of entertainment.
Inside the car, the theme is subtle and mostly stock but beautifully retrimmed by Suite Southern Upholstery & Auto Trim Ltd with much-needed new foam and seat springs, lots of new parts from Rare Spares and Kingswood Country, like door handles, mirrors, bolts, and clips, and a new (exchange) rear bumper to finish off the trailing end of the car.
A rush to finish it for the 2019 Caroline Bay Rock and Hop in Timaru meant that its shakedown voyage was a long one with about five hours of driving each way, but it handled it all with ease. Justin and wife Megan used and enjoyed the car for another three years, deciding in late 2022 that it needed a second full panel and paint to keep it looking mint and change the colour slightly, as they had never been 100 per cent happy with the first choice. Off to Shag and Andy at OSR Winton to repair a couple of rust issues, then a fresh coat of paint and a marathon effort of 3am finishes from Justin and a few good mates — Shannon, Dallas, and Evan — to finish it ready for the Cromwell Classic & Hot Rod Festival in 2023.
This ain’t your father’s/grandfather’s daily family car anymore with a new fiery heart, low stance, and tough demeanour, but what’s next for this immaculate well-built classic HQ? Justin and Megan are just happy to drive the wheels off it, taking it to events, cruising with mates, and leaving a few smoky skid marks where appropriate.
Justin would like to thank his wife Megan for the endless late nights getting the car on the road and also all the great mates who chipped in their personal time to achieve seemingly impossible timelines for getting the car ready for events.
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This article originally appeared in NZV8 issue 218