Legendary playwright Oscar Wilde famously wrote: “Moderation is a fatal thing; nothing succeeds like excess.” While he penned that line in 1893, he could have been talking about the cars turned out by ProFlo Performance, which has redefined how angry and wild a pro street build can be in the 21st Century.

First published in the May 2025 issue of Street Machine

This 1969 Holden HT ute is the perfect example. It has show-stopping Kashmir White paint, beautifully smoothed panelwork, and custom bodywork touches, like many clean streeters. But it also sits on a heavily revised chassis that allows it to roll on a set of customised 20×5.5 front and 24×15 rear wheels. The engine bay doesn’t feature a small- or big-block Chev, Iron Lion, or LS; instead, there are 768 cubic inches of Sonny Leonard mountain motor in there.

With such a huge amount of metalwork required to fit a 12.5-litre engine and all the hardware that goes along with it into a first-generation Kingswood ute, you’d assume that ProFlo’s customer must’ve brought them an absolute dunger to cut up. But that isn’t how it happened.

“The customer supplied a mint, stock-standard car,” laughs ProFlo’s Paul Sant. “It was that stock beige colour a lot of the HK-HTs are, but he wanted the signature ProFlo look, so we pulled it apart and cut it up!”

ProFlo’s distinctive contemporary pro street look requires plenty of clearance for big wheels and a ground-pounding ride height, but also very clean, shaved and smoothed aesthetic details. To handle this, Paul and the team gutted the cream-puff ute and cut out everything behind the bench seat.

This allowed them to add in a Castlemaine Rod Shop independent front end, which they had narrowed to suit the 20-inch front wheels. They added chassis connectors, a custom transmission and tailshaft tunnel, stretched rear wheel openings, and a whole new rear end. Replacing the weedy leaf springs and spindly Salisbury diff is a ProFlo-designed and fabricated rear end featuring a parallel four-link, wishbone locating bar, and a sheet-metal nine-inch diff.

“The rear of the car has been completely rebuilt,” says Paul. “We cut it all out and built a new structure there, and all up, from when we started until the car was finished and driving, there was around two-and-a-half years of work.”

Over the past few decades, ProFlo has become renowned for building ballistic engines, with their blown, turbo and aspirated combos being featured in some of Australia’s toughest street, event, and race cars. However, the team didn’t have to grind hard on the HT’s combo.

“The customer bought the engine from a drag car and it had just been freshened-up, so we basically put it straight in the car,” says Paul. “We still had to do a bit of work to it, as it was set up for carbies. So we changed it to EFI, partly to get everything low enough to fit under the bonnet, but also because we were no longer running it on race fuel, and the carbs couldn’t provide enough E85 to the engine.”

Swinging a mountainous 768ci, the big-dawg bent-eight runs a Brodix 5.0-inch bore-space block, SAR wedge cylinder heads, Bryant billet crank, GRP billet alloy rods and 14.5:1 Diamond pistons. The window-shaking thump-stick is a custom solid-roller from Sonny’s, working 11/16-inch Jesel lifters, Smith Brothers pushrods, SAR shaft-mount rockers by T&D, PSI valve springs, and Manley titanium valves, while the oil is circulated through a five-stage dry sump set-up.

The combo is controlled by a FuelTech FT600 ECU, running on E85 due to the high static compression ratio. Air is drawn into the Sonny’s single-plane bolt-together intake manifold through an Accufab throttlebody, while spent gases are blasted out through ProFlo-made custom 2.5-inch primaries to a 3.5-inch twin system.

“I believe it makes around 1500hp,” Paul says. “Fitting the engine wasn’t super-difficult. I don’t think we moved the firewall much at all; it wasn’t like the 940-cube Sonny’s Torana we did.”

A converter from Shotgun Performance and a TH400 auto built by Transmission Specialties live behind the big-inch engine, handling all the hurt it can provide. They needed to be nuclear grade, because while the customer isn’t looking to run numbers, he’s also not going to be shy with the ute, either.

“He’s not going to race the car, I don’t think,” says Paul. “This was always intended to be a street and event car, for things like Powercruise. So it will still see plenty of work, but I don’t think he’s going to be putting radials on it and running a number.”

When your ride already features numbers like 1500hp and 768 cubic inches, do any other digits really matter?

BLOCK PARTY

The enormous 12.5-litre engine in this HT is no over-stroked big-block from Chevrolet, Ford or Chrysler; it’s a design from Sonny’s.

Sonny’s Automotive Racing (SAR) is a name steeped in history across drag racing, tractor pulls, boat racing and street racing. Founded in 1968 by the late Sonny Leonard, SAR became renowned for pushing enormous engine combos, from 600 cubic inches all the way up to 1000.

Often referred to as ‘mountain motors’, these enormous donks saw duty in a huge range of racing and street cars, and found particular fame in the IHRA Pro Stock classes in the mid-70s, when the IHRA switched its Pro Stock rules up to remove the limit (or penalties) on engine capacity. The spectator stands were soon heaving, and the new Mountain Motor class saw a rush of development on gigantic engines, pushed hard by Sonny’s, Jon Kaase, and others.

Sonny’s biggest brute came in 2012, with a 1000ci (16.5L) V8. Actually displacing 1005ci, this engine’s specs are almost beyond belief, with a 5.22-inch bore, a 5.875-inch stroke, and 2200hp. With 17:1 compression, it was turned to 8200rpm – mind-boggling given the size of the crank – and made those 2200 horses without any forced induction or nitrous.

We’ve seen huge-inch Sonny’s combos in Aussie cars, with Michael ‘Gup’ Gilbert’s 727ci Hemi-headed VE HSV famously driven by Freiburger and Finnegan on an early episode of Roadkill. ProFlo used a 940ci nitrous combo for its customer Milan’s LJ Torana, which we featured in our February 2020 issue, and Rob Maggio’s LX Torana (SM, Yearbook ’23) boasted a 1000hp, aspirated 615ci Sonny’s fatty.

PROFLO PERFORMANCE
1969 HOLDEN HK KINGSWOOD UTE

THANKS
Paul and the team at ProFlo Performance; Jason at Kustom Paint; X-Trim Motor Trimming; Mark at Ontrak Auto Electrical; OAC Engineering; Alloys Chrome & Polishing; Mikey’s Garage; Protilt Towing.