DIESEL power has always been a bit of a black art. We know that highly boosted versions can make truckloads of torque, and that going fast with one seems to involve tons of black smoke and long periods of turbo spool. But we don’t get to see a whole lot of people messing with them in the world of drag racing.
About five years ago, Queensland-based brothers Luke and Scott French of GSL Fab adopted a beat-up, ex-mine Land Cruiser truck, and their experiments with making it go faster have sealed their reputation as boosted diesel gurus.
In 2018, their twin-turbo V8 Land Cruiser took the title of the quickest diesel sedan-style car in Australia, with a 10.95@119mph pass. It’s now making more than 1200rwhp and has taken the outright record to the tune of 8.93 over the quarter-mile.
As a side note, Stephan Vanderhee's diesel-powered dragster ran a 10.64-second pass at 123mph, back in 2012. He's currently reworking the car and aiming for the seven-scond zone.
This 79-series pick-up has been tortured in every possible way and is still kicking. It’s seen more evolutions than the iPhone, going from boosted work hack to all-out race rig.
“The great thing about this set-up now is that you can take all the bolt-ons off the engine, put them on a factory motor and you could race it for about eight months before you needed to touch it,” says Luke.
It was only through painstaking trial and error that GSL got to this point, a process involving a carousel of turbo systems and near-endless fabrication work. Nearly everything was done in-house, with Scott taking care of the tuning side.
From the outset, Luke and Scott went for the biggest Bosch fuel pump they could find, with a 14mm stroke. It delivers 9.5 litres per minute at 16MPa. According to Luke, that’s enough fuel to run two D11 bulldozers. With the capacity to feed in as much fuel as they could ever dream of, the boosted evolution began with the first upgrade from the dual 42mm factory turbos to twin 50mm variable-vane units. This produced 200rwkW (268rwhp) and 650Nm (479lb-ft) of torque, and a 16-second timeslip at the track. Early days.
“We then went to bottom-mount compound turbos, back near the gearbox,” recalls Luke. “We could see that the stock log-style manifold was just not going to do the job we needed, so we fabricated a set of two-inch logs that have worked great through the whole process.
“Next we went with a 2850 Garrett as the primary turbo, which all the drift guys were using at the time, and a 3582, which was a Skyline turbo. While all this seemed great in principle, we fought oil scavenging issues from the outset and never got a handle on it.”
Eventually they reverted back to a top-mount set-up, this time with a Precision 5858 as the primary turbo and a bigger 6870 rear turbo.
“The real step forward was moving from variable to gated turbos, which produced a big jump in horsepower,” says Luke. “It was a real learning curve with this combination, as we essentially needed a small turbo to get the party started and then we gated around the small turbo so it didn’t become a restrictor for the larger one.”
There were also many smaller changes that ultimately helped create a stronger final package, like the fitting of a fire ring in the block to seal compression.
“We never had an issue of lifting heads,” Luke explains. “We still run factory head bolts and heads, but we figured it would be a good long-term safety plan for the engine.”
Other changes included moving away from the stainless inlet manifold that was made early in the piece to a Fastlane Industries billet item. When it was time to start leaning on the combination, they pushed the boost up towards 60lb and the engine responded by making around 750rwhp.
“Later we leant on it even harder with 70-80lb of boost and nitrous as well, eventually making 970rwhp and running 8.93@143mph at Willowbank,” says Luke.
There’s no question that 970hp at the wheels is impressive, but the boys were not done there, and began installing what they call their bigger turbo set, with a 76mm Precision as the primary assisted by a BorgWarner 88mm. This produced 950 at the hubs without the aid of giggle gas. When nitrous was added, it cranked out an incredible 1190rwhp and 1770lb-ft of torque on just 42psi of boost, using only half the nitrous required by the previous set-up.
As the combo evolved, so too did the rest of the big rig. The stock transmission is long gone, and Queensland racer James Horan has built them a killer TH400 and one his own-brand torque converters. The 3500rpm Horan converter is a full lock-up item that the boys often engage at the top of second and into third gear to keep the load up and rpm down in order to make more power.
“Getting this up on boost is quite the challenge,” Luke says. “It’s very different to a petrol engine, as the rpm is a lot lower. You can’t just give it a belt of nitrous, as there is no turbine speed down low, so the nitrous shot has to be really carefully measured.
“Unlike petrol engines, we actually tighten the converter and the trick is to have the boost there when you need it and use the nitrous to cool the motor while you are trying to build power.”
With standard conrods, the engine has been getting buzzed to 5500rpm, but a newer version of the motor has just been released that has been fitted with Diesel Performance H-beam rods and forged pistons that will see 5800rpm. Because of the limited revs available, the rear-end ratio is low at 3.0:1, and they are swinging the tallest 315 radial they can get to stop the motor from over-revving.
This thing is really hauling the mail over the first half of the quarter-mile, with a pretty amazing 1.27-second 60-foot thanks to a full suspension set-up by Gazzard Brothers, with split mono-leaf rear springs, sliders and anti-roll bar. The diff is equally bulletproof, with a Race Products fabricated nine-inch and Strange Pro Mod-style bolt-through case.
It’s refreshing to get an insight into the diesel world beyond the black smoke and long-winded spool-ups. I’m sure we’d all like to hear how this story ends, but for now Luke and Scott will continue writing new chapters.
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