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780hp 1968 Holden HK Monaro GTS

By Iain Kelly | Photos: Chris Thorogood, 01 Feb 2020 Features

780hp 1968 Holden HK Monaro GTS

Niko Prommnitz's 780hp Holden HK Monaro proves you don't need to go buck-wild with a classic design to build a killer street car

AS THE price of classic tin soars, the chances of finding a good, clean base for a project dives. This means you sometimes have to jump on a car for sale, even if it isn’t exactly what you want, so you can beat the hordes of other punters wanting one.

This article was first published in the January 2020 issue of Street Machine

Holden HK Monaro

It also means taking a gamble that what you’re about to pay a king’s ransom for isn’t a complete basket case, which is the situation Queenslander Niko Prommnitz found himself in while chasing down a boyhood dream after a late-night text message.

Read next: Resto-mod 434-cube Holden HK Monaro GTS

Holden HK Monaro side

By not going over the top on the colour and suspension or chassis mods, Niko can easily change the look and feel of his HK. “It is only a bonnet, mild motor and a new set of wheels away from looking like a clean, stock Monaro,” he says. “I even have a set of Convo Pros here if I want to change the look up”

“One of my mates sent me a message about an HK Monaro with fresh paint for sale in Ipswich,” says Niko. “It was about two-and-a-half years ago when Monaros were going crazy and selling as quick as they became available, so I contacted the bloke to check it out. I made an offer on it and organised to get it back to my workshop.”

Read next: Twin-turbo LS-powered 1968 Holden HK Monaro GTS

Holden HK Monaro front

“Now the car is done I want to enjoy it and drive it, and definitely send it down the strip a few times,” says Niko. “I will have to see if I can keep it above a 10.5, as it isn’t ’caged and I don’t want to put one in and wreck all the hard work in there”

Unfortunately for Niko, the honeymoon period with his new purchase didn’t last long, and he soon realised the fresh paint was hiding some nasty surprises.

Read next: 615-cube Pro Street Holden HK Monaro - PRO HK

Holden HK Monaro

“I’d been looking for a Monaro for a while, but I wanted to buy one ready to go,” says Niko. “I knew I’d end up starting over with or modifying whatever I bought anyway. This car was more of a roller when I bought it, but I’m glad I went with it this way as it’s come out how I wanted”

“It was 40km back to my shop and the bog started cracking out of the left-rear guard on the tow truck,” he sighs. “One of the guys I used to work with told me that if I do a car build I have to take it to this guy Pat in Beaudesert.”

Holden HK Monaro

This Pat of which Niko’s former workmate spoke is, of course, Pat O’Shea, proprietor of top shop Pat’s Pro Restos.

“Two-and-a-half years later, I called Pat and he came out to have a look at the HK, and the rest is history,” says Niko. “Pat took it back to his shop to give the body and paintjob a going-over, then sent me photos of bog and rust, 10mm thick in some places, so there was no option but to get in there and fix it properly.”

Holden HK Monaro bonnet

Along with replacing the floorpans and bottoms of the guards, Niko’s Monaro also needed a new left-rear chassis rail, and it was this repair that really set the ball rolling for the comprehensive birthday it ended up enjoying.

“Pat recommended sandblasting the shell, as he reckons most Monaros are like this after 50 years,” Niko says. “He replaced the rail and mini-tubbed it utilising parts of the factory inner wheelarch so it still has that original look. There was so much panelwork throughout the whole build!”

Holden HK Monaro boot

The engine bay was smoothed out, with the drip rail along the top edge of the firewall shaved off, while the rest of the panels were massaged to the point of perfection. But when it came time for paint, Niko hit a roadblock.

“Initially I wanted to do it Silver Mink, but the original colour of the car was Ermine White,” he says. “I procrastinated when it came to colour and I’m so glad I went with white as it looks so clean and clinical. It shows off the HK’s lines and showcases how good the bodywork is.”

Holden HK Monaro engine bay

Niko’s Monaro has no problems with motivation thanks to 780 horses’ worth of small-block Chev up front. Built by Toca Performance, the 426ci mill packs Scat 4340 rods and crank and custom JE pistons in the bottom end, topped by Brodix 13-degree heads and manifold and a billet JE carburettor

One notable change from stock is the bonnet, which was needed to clear the 426ci small-block that Tony from Toca Performance screwed together for the HK.

Holden HK Monaro engine bay

“The way Pat’s incorporated the four-inch steel reverse-cowl, blending it into the factory lines and shape, makes it perfect,” says Niko. “I sat down with Tony from Toca and discussed what I wanted. Originally I planned to go with a hydraulic-roller cam set-up, but with guidance from Tony, we opted for the solid-roller and he then came up with a combo he knew would be reliable but also make great power.”

Holden HK Monaro underside

Wilwood four-piston calipers clamp disc brakes at all four corners, supplied with fluid from a matching Wilwood master cylinder. The Monaro rides on a McDonald Bros front end, ditching the stock box for a rack-and-pinion set-up, and swapping stamped steel control arms for tubular items. The suspension was set up and wheel-aligned by Suspension Dynamics in Capalaba

The stout solid-roller 426ci small-block Chev packs custom JE pistons and Scat 4340 rods and crank. Crower Severe-Duty lifters push beefy Trend 3/8-inch pushrods in the custom-ported Brodix 13-degree heads, topped by a port-matched Brodix intake manifold that wears a billet JE carb on top.

Holden HK Monaro interior

Southside Motor Trimmers handled the interior, which was done in simple classic style. “I didn’t want to go crazy inside, and I think the only thing that isn’t original-looking is the tacho and B&M shifter,” says Niko

An MSD distributor fires the 98RON fuel supplied by an Aeromotive in-tank pump, while dual 12-inch SPAL thermo fans keep things cool. Spent gasses exit through a custom stainless twin exhaust system with MagnaFlow mufflers keeping a lid on the decibels.

Holden HK Monaro dash

All up, the big-inch mouse motor turns a heavy-duty 780hp on pump fuel, spinning a 5500rpm converter and manualised TH350, while a shortened sheet-metal nine-inch diff filled with 3.9 gears and 35-spline axles is kept in place with a CalTracs mono-leaf rear end and AFCO shocks. Weld AlumaStar 15x9-inch wheels with beefy 295-wide ET Streets paint the black lines.

Holden HK Monaro rear seats

The HK’s clean build style and excellent sense of balance between stock and modified impressed judges at both MotorEx and the Queensland Hot Rod & Street Machine Spectacular. The Monaro took out a silver award for paint and bronze in bodywork in Melbourne, before snaring Top Street Machine, Best Standard Paint, Top Two-Door 1949-70, and a spot in the Top 10 at Brisbane. Niko, understandably, is chuffed.

“I always wanted a tough HK, and when I first saw the car completed I couldn’t believe it was mine,” he says. “I just want to drive it now; that’s what I built it for!”

Holden HK Monaro shifter

NIKO PROMMNITZ
1968 HOLDEN HK MONARO GTS

Paint: Glasurit Ermine White

ENGINE
Brand: Chev 426ci small-block
Induction: Brodix 13-degree
Carb: JE billet
Heads: Brodix 13-degree
Camshaft: Custom Comp solid-roller
Conrods: Scat 4340 H-beam
Pistons: Custom JE
Crank: Scat 4340
Oil pump: Moroso
Fuel system: Aeromotive in-tank pump
Cooling: 12in SPAL fans
Exhaust: Custom headers and system, MagnaFlow mufflers
Ignition: MSD 6AL

TRANSMISSION
Gearbox: TH350 three-speed auto
Converter: 5500rpm
Diff: Sheet-metal 9in, 3.9:1 gears, 35-spline Strange Engineering axles

SUSPENSION & BRAKES
Front: McDonald Bros coil-overs
Rear: AFCO shocks, CalTracs mono-leaf
Brakes: Wilwood discs and four-pistons calipers (f & r)
Master cylinder: Wilwood

WHEELS & TYRES
Rims: Weld AlumaStar; 17x4.5 (f), 15x9 (r)
Rubber: Mickey Thompson; front-runner 26x6.00 (f), ET Street 295/55 (r)

THANKS
Pat’s Pro Restos; Extreme Custom Engineering; Dash Original; Toca Performance; Bellarine Classic Auto Restorations; Suspension Dynamic