Dave Guilfoyle's 1973 Holden HQ GTS Monaro - TUFGM8

Fat rubber, slammed stance and a 500rwhp aspirated small-block Chev make this HQ coupe a killer cruiser

Holden HQ Monaro

SOME people know how to build a certain make and model of car, and Dave Guilfoyle is one of those blokes. His Whipple-blown, LS-swapped VL Calais and his wife Jodie’s LX hatch have both been stunners, along with a laundry list of other cool rides they’ve enjoyed, but Dave has an uncanny knack for building righteously tough and clean HQ Monaro coupes.

First published in the March 2021 issue of Street Machine. Photos: Chris Thorogood

Feast your peepers on this Cyan Blue example and delight in the way he’s incorporated all the cool factory styling Aussies love about Holden’s iconic 70s muscle car. And then check the way he’s dialled up the aggro through fat Weld rollers, and that detailed, corn syrup-chugging, solid-roller 421ci small-block under the bonnet.

Street Machine Features Holden Hq Rear
“Not long after I got it, I pulled the coupe off the road to change a few things,” says Dave. “The first to go was the satin Center Lines, plus we flow-coated the car at Brame’s. I did the blackouts, grille, headlight surrounds and all the GTS badging to match the look of MRGM8”

Dave’s other HQ, his Purr-Pull coupe MRGM8, was featured on the cover of our December 2015 issue with a show-finish blown 502 big-block, and then on the cover of SM LSX Tuner #6 after he flicked the BBC for a Magnuson 2300-inflated 427ci LSX. For the blue car, however, there was to be no forced induction.

“I wanted this one a little different to MRGM8, but with a similar theme,” says Dave. “MRGM8 has the blown E85 427 LSX, and this one has the angry E85 aspirated small-block. It’s good to have the best of both worlds!”

Street Machine Features Holden Hq Side

While it is awesome to say you own two HQ Monaro coupes, it took Dave giving up a treasured member of the Guilfoyle fleet to bring the blue two-door home.

“A mate bought the coupe a few months before I got it,” Dave says. “He sent the car up to me a few weeks later and said: ‘If you want to buy it, then buy it. If not, finish it off to sell for me.’ I could see it was a quality two-door, but it needed to be finished off right.

Street Machine Features Holden Hq Boot

“To buy the coupe I had to sacrifice a car I’d owned for over 20 years: my 1000+hp supercharged V8 VL Calais. I had progressed the car over the years, but to run the times I wanted and keep it fully legal in Victoria, it was not going to happen without spending more money on it. My mate Adam said: ‘Let’s do a deal,’ which made the decision easier, as I could swap my street/race car for another HQ coupe that I could drive anywhere and at any time without worrying about police like I did with my VL.”

While the blue coupe was a neat car, Dave tidied up some cosmetics so it looked like a true sister car to MRGM8, with GTS blackouts and badging. He then got on with cruising the car, but he wasn’t satisfied yet and dove into the suspension.

Street Machine Features Holden Hq Rear Wheels
That awesome slammed stance wouldn’t work without the 17x4.5 and 15x8 Weld V-Series rollers wrapped in 26x6x17 M/T rubber on the front and Nankang 275/60R15 tyres out back. The Monaro rides smoothly on Pedders WB springs and Competition Engineering three-way adjustable shocks at the pointy end and reset King springs and custom Pedders shocks on the rear

“The stock rear end just wasn’t right, especially when part of our business is tubbing cars!” he laughs. “I modified the original tub to fit a 275 ET radial but also have the car sit nice and low in the rear. I also gave the complete undercarriage a makeover, with new suspension all ’round, including ball joints, bushes and the like.

“When the Weld V-Series wheels were fitted, it had the look I’d pictured, so we cruised the car all last summer like this. But while it had the look I wanted, the mild small-block and converter were just not cutting it.”

Street Machine Features Holden Hq Engine Bay 2
The oil system starts with a custom 6.5L Russell oil pan, while a Shark Tooth high-volume oil pump and upgraded ARP shaft ensures solid supply of the black gold. Up front, a three-core brass HQ radiator, modified BA Falcon thermo fans and Davies Craig fan controller keep the temps down

Dave sold the Cyan coupe’s bent-eight to a mate and put the feelers out for a stout combo. His cousin Simon Hollingworth runs SJH Race Engines, but COVID was making it tough to source parts to build his own, so Dave figured he’d find a runner and make that work.

“I wanted a 421ci small-block and one came up for sale in SA that had gone 9.5 in a Torana, so I bought it and got Simon to check it over,” Dave explains.

Street Machine Features Holden Hq Engine Bay
Dave and his better half Jodes put bulk work into the engine bay, with a set of Shaun’s Custom Alloy billet rocker covers, Reidspeed polished billet heater plate and billet bonnet hinges. “We cruised it around as much as we could with COVID restrictions, and it felt good to be driving a tough aspirated engine with a big converter again!” Dave says

The nickel-tough mouse motor uses a Dart block as the base with a Scat 4340 crank, custom CP pistons and Scat H-beam rods, plus a custom 267/275/106 solid-roller bumpstick to push the Crane Ultra Pro Series lifters and pushrods. A pair of AFR 220 heads have been paired with PAC Racing valve springs, with a custom 1000cfm Pro Systems carb and Edelbrock Vic E-series single-plane manifold topping the tower of power.

Drinking a diet of straight E85 thanks to a pair of Holley HP 150 pumps, the grumpy little-block fires its pots thanks to an MSD Pro-Billet dizzy, MSD 2 coil and an MSD 6AL-2 brain box. Spent gases are evacuated through HPC-coated Pacemaker extractors and down a twin three-inch exhaust from Blitz Exhausts. All up, the big-inch little-block made 509rwhp aspirated, though Dave has a 250-shot of gas ready to deliver an XXL Gapplebees meal if required.

Street Machine Features Holden Hq Interior
As HQ GTS interiors are a killer place to spend time from the factory, Dave didn’t reinvent the wheel and instead treated the coupe to some mild updates, including a fresh dash pad, a fish-scale dash fascia, a B&M Pro Ratchet shifter and some Auto Meter gauges. A Kenwood sound system is hidden away, with 4in speakers up front and 6in speakers under the parcel shelf

MDT got the job of building a tough manualised TH400 that sits behind a 5200rpm eight-inch nitrous converter, paired to the nine-inch Dave built when he mini-tubbed the HQ. It’s a Strange Engineering case packed with the full fruit basket including 31-spline billet axles, a Truetrac centre, alloy pinion support and 3.7 gears.

“We have definitely put some kilometres on it lately with car meets coming back after COVID, and we don’t have much more planned for it at this stage apart from cruising it as much as we can,” says Dave. With such a killer pair of HQs in the shed, the only dilemma would be which one to take out!

Street Machine Features Holden Hq Onroad


Paint: Cyan Blue and Glacier White

Brand: 421ci Dart small-block Chev
Induction: Edelbrock Vic E-series single-plane
Carb: Pro Systems 1000cfm E85
Gas: 250-shot
Heads: AFR 220
Camshaft: Custom 267/275/106 solid-roller
Conrods: Scat H-beam
Pistons: Custom CP
Crank: Scat 4340
Oil system: Shark Tooth pump, ARP shaft, custom Russell 6.5L pan
Fuel system: Two Holley HP 150 pumps, 8AN lines
Cooling: HQ brass three-core, BA Falcon fans
Exhaust: Pacemaker extractors, twin 3in, Blitz mufflers
Ignition: MSD 6AL, MSD-2 coil, MSD Pro-Billet distributor

Gearbox: MDT TH400, manualised
Converter: AK 8in 5200rpm
Diff: Strange Engineering 9in, Strange alloy pinion support, billet 1350 yoke, Truetrac, billet 31-spline axles, 3.7:1 gears

Front: Pedders WB springs, Competition Engineering three-way adjustable shocks, Pedders heavy-duty sway-bar
Rear: King reset springs, custom Pedders shocks
Brakes: RDA HZ discs (f), RDA HQ Kingswood (r)
Master cylinder: HZ Statesman

Rims: Weld V-Series; 17x4.5 (f), 15x8 (r)
Rubber: Mickey Thompson 26x6x17 (f), Nankang 275/60R15 (r)

My amazing wife Jodes for enjoying the same passion as I do; our kids Ash, Shay, Kaneo and Claire who are old enough to enjoy the cars with us; Simon at SJH Race Engines; Matt and Bee at Brame’s Paint & Panel; Allan at Blitz Custom Exhausts; Adam at Tyrepower Melton; my brother Shaneo, my dad and sister Kal at Autobarn Ballarat; V-man; Chewy at Repco Ballarat; Jamie DA1 Smith; Matt Despirt at MDT; Daniel at Reidspeed; the boys at Garageworx Tuning; John at Raceparts Melbourne; Chris’s Differential Service; Rod at Rodbilt; Tribey at WBC; Michael at SA Engine


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