First published in the December 2007 issue of Street Machine

It’s pretty loud — you know it means business when you hear it running.” That’s what Troy Higgins has to say about his crazily powerful HSV GTO. But what sounds like it means business to Street Machine readers would probably have your average citizen heading for the bomb shelters.

“Yeah, under hard acceleration it is very loud,” Troy is forced to admit.

Why? Well it might have something to do with the 427 cubes under the bonnet being force-fed 20lb of intercooled air thanks to a Vortech YSi blower, and it might have something to do with dumping through a 3.5in twin system. You’d imagine it’s good for a few horses but would you have guessed a whopping 1150hp at the rear treads?

Troy bought the GTO a few years ago as a private sale with the intention of creating a horsepower monster right from the start.

“I just wanted to be different, take things to the next level,” he says.

Working as a heavy duty plant mechanic in Kalgoorlie, WA, Troy is like a lot of blokes in that mining community; on a good wage without much to spend it on. This is why we see a lot of cool machinery from that region of the world.

“I was debating whether to buy a new one or not,” he says, “but I decided I wouldn’t have enough money to start with a new one.”

Since a brand new GTO coupe was around $85,000 we can understand that Troy would want to save a few bucks by picking up a good used example. He found one in Perth with 30,000 clicks on it. “It had a rip in the seat but other than that it was faultless,” he says.

With the car in hand and pennies saved, Troy headed to Mark’s Workshop, a place that should be well known to regular readers. It’s been the birthplace of many big grunters over the years and is the logical place to go for a high horsepower build in WA. “We built it to make 1000hp at the wheels,” says workshop owner Mark Else, who had some ideas of what he wanted to do with the powerplant. “My design philosophy was to build something that flowed very well.”

In other words, he wanted to build an engine that didn’t simply rely on cramming in absurd amounts of boost to make power.

Initially, the basis for the engine was an exotic and very expensive C5R block but, as other builders have found, the high performance alloy block just couldn’t handle the power.

“We were fortunate that when we discovered the problems with the C5R block, the new LSX block was only a few weeks away from release,” Mark says. When it comes to Gen III engines, the new cast-iron LSX block is the big kahuna. It’s capable of supporting 2500hp, has six-bolt mains, six head bolts per cylinder and the tall-deck version can take a 4.5in stroke, which means you can take it out to more than 500 cubes (8.3-litres) if you want. Not bad for a small-block!

Mark didn’t want to take the block out to the limits and deemed 427 cubic inches enough to get the job done. Being the first to use one of the new LSX blocks, it was a learning experience for all involved — no-one had heads available in the six-bolt configuration and while the four-bolt heads fitted, they didn’t have the same clamping force. Mark wanted to use the brilliant ETP heads so he contacted the guys, discussed requirements and obtained a customised set in the new six-bolt style. Nowadays ET Performance has the six-bolt style as a regular option but it was just another area where Mark and the guys had to break ground with this build. Mark’s Workshop oversaw the car’s build-up, with assistance in some areas — John Lloyd from Street Quick Performance handled the engine assembly. Tuning the factory Delphi ECU (using EFI Live) was a team effort which included Mark, his wife Katherine, and Daniel Collins from Chipmaster.

At first Mark wasn’t sure that the Vortech V7 YSi would be able to do the job, seeing as it’s officially rated at ‘only’ 1000hp. By using a custom intake bellmouth and a custom intercooler set-up that directs the air through the radiator support dress-panel, Mark reduced the restrictions before and after the blower, and the proof of how effective that was is in the results. But using the nicely curved intercooler top caused some issues of its own: with 20psi of boost the curved alloy tried to straighten out, which required some extra strengthening: “You could straighten out a banana with enough boost,” Mark reckons.

At full boost the GTO has made 1150rwhp on Mark’s twin-retarder dyno. It backed up that figure with more than 1000rwhp at Perth Auto Salon on a single-retarder dyno which maxed out at just 4000rpm. On both dynos the car struggled with wheelspin and Mark believes they haven’t seen the best from the motor yet.

“I’d have to honestly say it’ll make around 1200hp at the wheels,” Mark says. “Being familiar with 800 and 900hp cars, this thing feels twice as strong.”

Under the rear sits a custom alloy drop-tank that feeds a heavy duty fuel system sporting six pumps. Rounding out the rear end’s looks is a pair of custom alloy exhaust tips.

“The look of the car was always intended to be very clean — nice and sharp. It’s a very neat looking thing,” Mark says.

For dyno work the GTO runs on Martini Racing 104 octane just for peace of mind but the guys detune it for the street where pump 98 octane fuel is used instead. They don’t change pulleys to drop the boost — Mark reckons the air cleaner takes 2psi straight off the top and then he fits a special restrictor plate to the blower intake that drops the boost down to 10psi. Dropping the boost and retarding the timing a few degrees calms the HSV coupe down but it stills make masses of horsepower.

Overall, it took 12 months to complete the horsepower upgrade and Troy’s pretty happy with the result. “I wouldn’t mind doing a few more shows,” he says. “It sticks to the road quite well but I might upgrade the brakes.” Other likely improvements include 10in wheels to fill out the rear guards and a tougher driveline to handle all that grunt.

Troy’s wife Tamara doesn’t seem to mind the GTO either: “She’s backed me all the way,” he says. And when Troy suggested that he might get his wedding ring engraved with Chevy symbols, “she reckoned it was a good idea”.

FEEDING THE FIRE

When it comes to making horsepower you need fuel to burn and enough oxygen to keep the fire alight.
The oxygen part is easy — the Vortech YSi supports 1000hp on pump gas. But that much grunt takes lots of juice.

Bolted to the frame is a custom 12-litre surge tank fed by two high performance Walbro pumps in the alloy drop tank. That keeps fuel over the pick-ups for the four Bosch 044 pumps on the sides of the surge tank. Inside the surge tank, the pick-ups are near the bottom. The two lower pumps run constantly, as do the two in-tank Walbro pumps. The upper two pumps cut in when boost hits 7psi. A pair of Magna Fuel regulators feed twin ½in fuel lines. It’s a dead-head system so there are no return lines; regulators bypass excess fuel back to the top of the surge tank. With pressure at 100psi there’s no need for boost referencing on the regulators; the fuel supply is constant and massive.

1. 12-litre surge tank, internally plumbed pick-ups

2. Bosch 044 600hp pumps — always on

3. Bosch 044 600hp pumps — boost-activated at 7psi

4. Magna Fuel bypass regulators set at 100psi

TROY HIGGINS
HSV GTO COUPE

THANKS
Wife Tamara; Ian Creeley, Snowy, Daniel & Mark McKay; Mark’s Workshop; Street Quick Performance; Chipmaster.