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Elite-level 496ci big-block 1970 Holden HG Premier

By Andrew Broadley | Photos: Chris Thorogood, 01 Aug 2018 Features

Elite-level 496ci big-block 1970 Holden HG Premier

Glenn Coburn's street-legal Holden HG is equally at home at the strip, in the elite hall or out cruising

This article on Glenn's HG Premier was originally published in the March 2013 issue of Street Machine magazine

LIKE it or loathe it, very few perennial Elite Hall favourites are genuinely, reliably and regularly street driven. Of those that are, even fewer are capable of consistent bottom 10-second quarter-mile passes.

Holden HG Premier onroadIt’s fair to say Glenn Coburn’s stunning and certified street-legal HG Premier is in a select band and one hardcore street machine.

Watch the video: Glenn's VB Commodore at Bathurst Autofest

“Back in 2007 I did about 18 months of solid racing with it. Eventually it went 10.1@135mph at Willowbank but it ran 10.2s all day,” Glenn, part owner and head painter at renowned Sydney panel shop Exclusive Customs, explains.

Holden HG Premier sideTo fit the new 18x7 and 19x10 Showwheels Indy billets, mini-tubs and pumped guards all ’round were necessary

His long and colourful association with the Prem pre-dates his 14-year ownership. It once belonged to an apprentice beater named Chris Warwick who worked with Glenn’s dad, Rick.

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“That was in the late 80s, and at that stage it had a 308, Muncie four-speed and a 10-bolt. Chris did all the panel work and Dad painted it. He then took it to Summernats three times, where it made Top 60.

“I always loved the car and in 1996 I finally convinced Chris to sell it to me. I drove it for about a year, then pulled it apart to put the big-block in it.”

Holden HG Premier bonnetSaid block is a Hercules-built Chev that beats the 427ci capacity implied on the numberplates by 69 cubes, weighing in at a hefty 496ci. Packing a Scat crank, Carillo rods, Camtech cam and forged Arias slugs with CNC-ported Brodix Big Brodie heads, it stomped out an impressive 680hp and 650ft-lb at the crank before it was lowered into the bay and secured to the chassis via an engine plate.

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Behind that, a beefed-up two-speed ’Glide runs a 4000rpm Dominator converter, while the 4.11-geared 35-spline nine-inch features Mark Williams internals.

While the car hasn’t been raced for some time, the only mechanical change has been ditching the high-rise manifold and 1150 Dominator for an Edelbrock dual-plane and a 950cfm carb. With a 14in drop-base air filter, it now clears a standard bonnet.

Holden HG Premier under“It has the same amount of horsepower it’s always had but a little bit more torque, so if anything it might go a bit better,” Glenn says. “There’s probably a nine in it; it’d just be a matter of setting up the suspension. I really should run it again — it’s all ANDRA teched and ready to go.”

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As impressive as a stack of low 10-second timecards is for a street-legal cruiser, these days the car is much better known for its accomplishments in the show arena, which are due in no small part to the skills and commitment of Glenn and his panel-beater brother Jason, whose LX hatch we featured in the Nov, ’12 issue.

“Slowly our business began to change and we started to take on a lot more show cars, so three years ago I pulled the HG down for a tidy-up, repainted it and started competing with it at shows,” Glenn says.

Holden HG Premier exhaustThe quality of the paint and bodywork aptly reflects Glenn and Jason’s talents in their respective trades, and the razor-sharp Prem has amassed a swag of paint and body awards — and multiple Summernats Top 60 berths — since.

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The front and rear quarters have been pumped by an inch but it’s done so neatly that you’d do well to notice. Glenn loaded his gun with PPG Kings Gold and layered it on, followed by a Gold Flamboyance overlay. The resultant finish is spectacular; sensitive to the original colour but with a beautifully subtle fleck that’s noticeable only in the correct light.

At the same time, the engine bay underwent an overhaul and it too has attracted its fair share of tinware. Jason expertly smoothed the inner guards and firewall before Glenn gave them a lick of paint.

Holden HG Premier engine bayThe 680hp big-block is superbly detailed. Just because it’s fast doesn’t mean it can’t be pretty as well!

They’ve colour-coded just the right amount of hardware in there too, including the block, Billet Specialties rocker covers, air filter housing, master cylinder, fan shroud, radiator hose fittings and CSR water pump snout. The balance is either polished or chromed to perfection.

The cabin is one area of the car that hasn’t been subject to continual improvements, and aside from the addition of a six-point rollcage and a Pioneer stereo, it remains as it was 15 years ago.

The fact that it’s still in such good shape despite regular use is evidence of how well-maintained the car is. The cosy standard-issue Prem seats were retrimmed in black leather, while the steering wheel was pinched from a Monaro of the same vintage. A Hurst shifter and Auto Meter instruments are the only other contemporary concessions.

Holden HG Premier engine bayGlenn has done exceptionally well with the Prem on the track and in the judging arena over the years but he’s adamant that it’s never been at the expense of it being a genuine street car.

“There are plenty of things we could change to take the car further but I built it to race and drive and that’s the way I like it,” he says. “I normally take it out at least once a fortnight but now that I’ve put the lower-profile intake on it, I’m about to slip some 3.25:1 diff gears in, fit air con and really drive the wheels off it.

“I want to do more cruising and I’d love to drive it to events like Cooly Rocks or cruise to Mum and Dad’s caravan down the coast for the weekend. I’d even like to start driving it to work a couple of times a week. That’d be cool!”

Holden HG Premier interiorThe black leather is well over a decade old but still in fantastic condition. It’s survived two rebuilds so far!

HIT THE STREET

NOW it’s proven its mettle by making the Elite Hall several times, Glenn plans to really start racking up the miles in the Prem and has set his sights on the Street class at Summernats 27.

“It’s just awesome to drive and with the new diff gears and a few mod cons it’ll be even better,” he says. “I like the car the way it is and I don’t really want to change it to keep pace with the Elite cars. I’d like to see how it goes in the Street class and maybe have a crack at Top Overall Street. It’d be cool to be able to drive the car to any show in Australia and win trophies, and I think in a way that proves more than doing well in the Elite class.”

GLENN COBURN
1970 HOLDEN HG PREMIER

Colour: PPG Kings Gold with Gold Flamboyance overlay

ENGINE
Brand: Chev big-block, 496ci
Inlet: Edelbrock Air Gap EnduraShine
Carb: Holley Ultra HP-series 950cfm
Heads: Big Brodie 3 CNC-ported
Camshaft: Camtech
Conrods: Carrillo
Pistons: Arias 11.5:1
Crank: Scat
Oil pump: High volume
Sump: High Energy
Fuel: PULP 98 octane
Fuel system: Holley mechanical pump
Cooling: VS V8 radiator, EL thermo fans
Exhaust: Twin 3in stainless system, 2¼in headers
Ignition: MSD 6AL, MSD dizzy, MSD leads

TRANSMISSION
Gearbox: Powerglide, manualised
Converter: Dominator 8in 4000rpm
Diff: Nine-inch, Mark Williams 4.11:1 centre, Mark Williams 25-spline axles

SUSPENSION & BRAKES
Springs: Pedders (f), Pedders with Caltracs (r)
Shocks: Pedders 50/50 gas (f), Pedders air shocks(r)
Brakes: HQ discs, DBA Gold rotors (f), EA discs DBA Gold rotors (r)
Master cylinder: HG V8
Steering: LH rack and pinion

WHEELS & TYRES
Rims: Showwheels Indy 18x7 (f), 19x10 (r)
Rubber: BF Goodrich 245/45/18 (f), 295/35/19 (r)