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!
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.
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!
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!
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!
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
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