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HSV XU6 - The P-Plate Loophole!

The HSV XU6 is one of the quickest cars suitable for Victorian P-plate drivers. And see what happens with a few mods...

Words by Michael Knowling, Pix by Julian Edgar

Click on pics to view larger images

At a glance...

  • The underrated HSV XU6
  • Legal for Victorian P-platers
  • Huge power gains with minimal mods
  • Look out Holden/HSV V8s!
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If you’re a P-plater living in Victoria, Australia, you have good reason to be frustrated: local laws make it illegal for you to get behind the wheel of any ‘high power’ vehicle. The official definition of a high power car is one having a power to weight ratio in excess of 125kW per tonne or an engine capacity to weight ratio over 3.5 litres per tonne. Too bad if you want to buy a Clubsport, WRX, Honda VTEC or pretty well any other desirable car you can mention.

But there’s one vehicle that j-u-s-t slips below the official threshold. The HSV XU6!

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With a supercharged 3.8-litre V6 providing V8-rivaling torque, the XU6 is substantially quicker than many high power cars on that black list. And that’s exactly why George S. bought one.

“When I got rid of the Series One RX-7 that I owned I wanted to buy a Clubsport or at least some kind of 5.7-litre Holden. But the P-plate regulation stuffed that up,” he says.

“Then I came across the XU6. It’s the most powerful HSV I can legally drive and I knew you can get intercoolers and lots of other parts for them. With slicks and a high stall converter I reckon it should be pretty easy to get high 11s.”

This might sound pretty optimistic but keep in mind the US-spec Buick Grand National (which runs essentially the same 3.8-litre V6 with a turbocharger) are easily running deep into the 10s.

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In standard form, the XU6 runs about 6 psi boost from its Eaton M90 blower to achieve a factory quoted output of 180kW at the flywheel. Fired up on the DynoLog chassis dyno at Nizpro, George’s car pushed a surprisingly high 161kW at the back wheels.

Unfortunately, it’s difficult to achieve massive power gains with this engine without some form of charge-air cooling. George says intake air temperature was 155 – 160 degrees Celsius on just 6 psi boost... But rather than go for an off-the-shelf intercooler kit, George decided to go for a double-whammy – something that would lower intake temps and elevate power in its own right. Yep, we’re talkin’ nitrous!

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George went for a 90hp shot of gas which is injected in the cast alloy entry to the supercharger. A large nitrous bottle can be found in the boot – George says it’s big enough to give five or six quarter mile runs. The nitrous system and most of the other performance parts come courtesy of Perth company, FIT. The N20 injection slashed intake air temperatures, helped seal the supercharger lobes for a slight boost pressure increase and unleashed a chemical advantage. Power? How ‘bout a 47 percent gain – 236kW at the wheels!

Immediately following this, a bolt-on supercharger pulley upgrade was fitted to increase boost to 10 psi; nothing excessive. This vaulted power to 252kW at the wheels. That outa wipe the pitying smirk off the face of any LS1 driver!

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In this guise, George took the car to the drag strip but encountered problems with a slipping supercharger belt. The best time was a dissapoionting 13.8 second ET but a replacement Gates belt is now fitted to ensure the supercharger has slip-free operation.

Following our photo shoot, George also treated the car to higher ratio aftermarket rockers. This has seem him lay down a seriously fast 12.1 second ET. Apparently, the car is now running out of fuel at max power and George is planning to install a high-flow fuel pump. Power is expected in the vicinity of 290kW at the wheels.

All this while retaining the stock HSV exhaust and standard management - unbelievable!

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George has left the standard HSV rims in place to help maintain a stock appearance although the ride height has been brought down about one inch thanks to Pedders lowered springs. The interior is also much how it left HSV and includes sports seats and instruments, drilled pedals and a HSV convenience pack in the centre console. The only changes are a Pioneer DVD/TV, JL Audio front splits and 6 ½ inch rears.

George doesn’t want to focus too much on attracting the wrong kind of attention so his planned mods are all under-the-skin. A high rpm stall converter and a shorter (3.45:1) diff ratio won’t increase power but should improve response and performance in everyday driving situations. Some form of engine management upgrade is also on the drawing board.

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But for now George is more than happy to keep driving his low 12-second XU6 which, according to official documentation, isn’t a high power vehicle.

Now that’s what we call stickin’ it to the man!


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+61 8 9472 7050

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