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GTO Gone Racing

A HSV GTO with a stroker engine and all the good bits to go weekend racing!

Words by Michael Knowling. Pix by Julian Edgar

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At a glance...

  • 6.2-litre stroker
  • Mal Wood 6-speed and KAAZ diff
  • Serious brake and suspension upgrade
  • Ferocious weekend track racer
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It’s unusual to find a car enthusiast who is 100 percent content with their machine. There are always some shinier wheels, bigger cams and sexier sub-woofers to catch you eye just when you thought you had everything sorted out... Well, Simon X is an exception. His sensational HSV GTO has everything he desires and he’s not interested in updating to the latest model.

He’s happy right where he is, thanks very much!

Simon’s car was featured in AutoSpeed back in 2002 (see Fly the Coupe) and since then it has comprehensively matured as a performance vehicle. Every area of performance has been addressed.

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The last time we saw this GTO it was running a cam and head package good for 271kW at the wheels. Simon says he spent a fair amount of time with different cam profiles chasing the power he wanted - Simon is a regular circuit racer and doesn’t like the idea of being left behind on the straights...

“With a really big cam in it the car made good power - but there’s a limit to what you can do by just changing the cam in the standard 5.7,” says Simon.

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Those big horsepower camshafts caused a bottom-end torque loss that Simon wasn’t content with so the next logical step was to bump up the cubic capacity (Simon isn’t a fan of forced induction). At this point, Simon sat down with F1 Performance’s trusted engine builder - James Young - and discussed approximate power output and engine application. There wasn’t a particular power figure Simon had in mind – he simply wanted an engine that could be driven without hiccup in traffic yet perform strongly on weekend racetrack assaults.

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The solution came in the form of a 6.2-litre (383ci) Eagle stroker kit teamed with heavy-duty L19 rod bolts and JE forged pistons providing a 10.8:1 compression ratio. The already ported cylinder heads were replaced with even more serious heads with bigger ports and polished combustion chambers. The camshaft is a big ‘un with specifications chosen by James Young. Stainless steel valves, Competition valve springs, heavy-duty retainers, 1.7:1 Yella Terra roller rockers and a Rollmaster double row timing chain complete the valvetrain. Multi-layer head gaskets are also used in the build.

The huge volume of gas exhaled by the stroker motor is channeled through a twin 3 inch Di Filippo exhaust with a custom rear muffler with an emphasis on reducing noise. Simon doesn’t want to attract the wrong kind of attention on the street. A pair of ceramic-coated Pacemaker 4>1 headers scavenge gasses from the cylinders.

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On the intake side, an over-the-radiator ram-air pipe draws air through a removable K&N panel filter.  Downstream of the ram-air pipe is a Starr throttle body connected to the stock intake manifold.

Simon says the newly built stroker motor delivers strong punch from about 4500 to 6800 rpm - 200 rpm shy of the rev limiter. The reset rev limit, altered fuel mapping and ignition timing come courtesy of LS1 Edit reprogramming software. No need to fiddle around wiring in a new computer or interceptor unit.

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Each of those long-sweeping pistons suck fuel from a 42lb fuel injector teamed with Wilson Manifolds rails, braided lines and an SX pressure regulator. A Bosch 044 Motorsport pump and surge tank live in the rear and guarantee uninterrupted fuel delivery even during the fiercest cornering and braking forces.

Fired into life on F1 Performance’s Dyno Dynamics chassis dyno, Simon’s GTO makes some impressive numbers. There’s bulk torque straight off idle and the muscle continues to flex to almost 7000 rpm where the car is pushing 355kW at the treads. That equates to almost 450kW at the crank – enough to see off pretty well anything that lines up alongside.

Heading further along the driveline you’ll find a 12 inch Mal Wood clutch and Yella Terra lightened steel flywheel. The stock T56 gearbox was also replaced by a Mal Wood 6-speed ‘box with carefully selected ratios. A Mal Wood tailshaft reaches back to the rear-end which is enhanced with a KAAZ mechanical LSD. A Harrop diff cover (which provides greater fluid capacity and improved cooling) is also installed.

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With the original 5.7 litre engine, Simon says the GTO handled progressively and was easy to control. But with stroker grunt now on tap, the car arrives at corners carrying a lot more speed and the handling needed more development. Previously, the car used a Quadrant/Bilstein set-up comprising springs, dampers and a front strut brace. It now uses Koni double adjustable dampers, King springs, Nolathane bushes and a Whiteline adjustable front swaybar. The chassis is also toughened with the addition of a rear strut brace and under-body bracing.

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The existing Harrop/DBA front brakes are carried over but Simon says a pair of six-pot CSC anchors will be soon fitted. The rear employs newly installed CSC four-pot calipers and slotted discs. Simon says the CSCs are a great product – they provide good value for money, good disc life and they stop well. A set of Race Brakes RB74s are used for the street while circuit duties call for PFC high-temperature pads. 

Interestingly, Simon also tweaks the chassis before each track day. Up to 4½ degrees of negative camber and 1.5 – 3mm of toe-out improves front end turn-in and mid corner grip. Front brake cooling ducts are also installed and the Monday-to-Friday Nexen tyres are swapped for soft an’ sticky Bridgestone RE55s.

Further preparation for track work includes the fitment of an engine oil cooler and power steering fluid cooler. It’s this kind of attention to detail that makes Simon’s GTO very quick and reliable – it’s no surprise that the car was the quickest road car at Winton Raceway during a recent weekend meet.

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Simon keeps an eye on the engine thanks to AutoMeter gauges for oil pressure and temperature. These are temporarily mounted in a custom alloy faceplate at the base of the centre console. They will soon be integrated into an OE satellite navigation trim panel.

The audio system stems from gold plated battery terminals and fuse holders into the standard HSV head unit. An Eclipse four-channel amplifier boost the output level and sends it to 6½ inch Focal front splits, 5 1/4 inch Focal rear splits and a pair of Rockford Fosgate 6½ inch woofers in the rear shelf. Simon chose these as a lighter weight alternative to large cone subs and says they work well - especially in the mid-bass frequencies. Sound deadening is installed inside the doors and side quarter panels to improve sound quality.

After around three years of development, Simon has his GTO exactly how he wants it – there’s no way you could tempt him with the latest batch of Holden/HSV Coupes. The only plan on the agenda is to put a higher number on the odometer – when you’ve finally pieced together your dream machine, you often find there’s simply not enough time for drivin’ it...


F1 Performance +61 3 9894 4228

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