Building reliable, four-digit forced-induction engines for street, skid and event cars is a skill that takes years to master, and Troy Worsley of Warspeed Industries has it down pat. However, he was recently presented with a new challenge: put together a 427ci LS-based donk for an off-road racing Trophy Truck.

First published in the August 2024 issue of Street Machine

While many of his most well-known street combos use iron blocks, Troy opted for an alloy Concept Performance LSR unit this time, which comes with billet main caps. “We use these in combos where we’re trying to keep the weight and heat down,” he explains. “These trucks race in events like the Finke Desert Race, and they’ll sit on 5500-8500rpm for the whole race, which is hours of stress.”

The rotating assembly includes a Callies eight-counterweight crank running a four-inch stoke, with Oliver rods and custom CP pistons squeezing nearly 13:1 compression.

Swinging the valvetrain is a custom Comp solid-roller, which Troy says is “in the 270s for duration”, although he’s keen to keep its other specs quiet, as is normal for competition donks like this one. “For this class, the combo is limited to a 7.0-litre capacity. The cam specs are very important, and it has to work with the rest of the combo to provide not just the horsepower the driver needs, but also great response,” he explains. “These engines have to hang together at high rpm in an insanely tough racing environment.”

The heads are Higgins LS7 castings, with Crower roller rockers, Manton pushrods and Crower high-pressure lifters rounding out the important valvetrain hardware.

With so much strain and revs on board, Troy also had to go all-out on the oil system, so he fitted a Velocity dry sump. “It is a custom system, with the oil pump mounted under the engine rather than fitted to the side due to chassis rail clearance in the engine bay,” he says. “Velocity also built the custom stack injection. They modelled the engine’s specs, and we had to size the drive-by-wire throttlebodies for power and response. The base plate of the custom Unifilter air filter also had to be incorporated into the manifold. Unifilter then made the mesh filter box with a pre-filter and main filter.”

Keeping dust out is obviously hugely important for a Trophy Truck mill like this, so Troy set up filters on the breathers to ensure the hard-spinning donk doesn’t swallow any grit. “We had to Loctite everything and glue everything together,” he laughs. “Making power is the easy bit, but trying to get this engine to live in an incredibly harsh, high-stress environment is the real challenge. That’s why the engine is regulated to run at 10 inches of vacuum.”

So many unique challenges blew out Troy’s normally snappy timeline for knocking an engine assembly together, simply because everything had to be designed, tested and fitted. “Putting this engine together felt like I was taking one step forward and going three back,” he laughs. “That’s the nature of development, though. This is learning, and I was hoping to be a better tradesman at the end of it.”

The racing team shoved the engine straight into the truck as soon as Troy shipped it out, and it made north of 650hp at the wheels on a chassis dyno. That should give it enough oomph to tackle the deep sandy ruts of the Aussie desert!

GEAR SHIFTS

Small details like the billet RCD gear drive on the front of the engine had knock-on effects for other engine hardware. “The timing pointer isn’t the normal one, because fitting the billet gear drive meant the water pump wouldn’t fit like it normally does, and we couldn’t run an electric pump because of the electrical load on the system,” Troy says.

Warspeed Industries
ST Marys, NSW
warspeedindustries.com.au/