424ci small-block Chev mill by Horsepower Engineering

Turbocharged LS donks are not everyone’s cup of tea

Photographers: Mitch Hemming

THESE fandangled new LS engines are all the rage, and now that every man and his dog are hanging turbos off them, it’s a lot easier to make 700hp than it used to be. But turbocharged LS donks are not everyone’s cup of tea, and some blokes – like Queenslander Mark Roberts – prefer to do things the old-fashioned way.

This article was first published in the March 2018 issue of Street Machine

Mark has had this 424ci, naturally aspirated small-block Chev put together by Horsepower Engineering for his VH Commodore street-and-strip car. It runs a Dart SHP block with a forged Scat crankshaft, six-inch Callies rods, and custom CP pistons. The Crane solid-roller camshaft was ground specifically for this combo, and has north of .700in valve lift and somewhere in the neighbourhood of 260 degrees of duration.

The heads are hand-ported 23-degree Racer Pro items, fitted with T&D rockers and topped with a cast-alloy Edelbrock single-plane intake manifold and Quick Fuel Black Diamond 1000cfm carby.

The ancillaries are pretty trick, including the Barnes external oil pump, which draws the good stuff from an ASR pan. There’s also a crank-trigger MSD ignition system, Moroso vacuum pump and Meziere electric water pump, and the hand-built headers feature 17/8-inch primaries stepped up to two inches, feeding a four-inch collector.

“It’s a max-effort, 23-degree-headed ‘street’ motor that will see plenty of cruising as well as racing,” Mark says. “The goal was 700hp on pump fuel, and more again on race fuel. A lot of industry input has been invested into this motor, and we’ve made every effort to minimise friction loses – like the custom ring pack – to make the best power we can with a 23-degree, standard-layout cylinder head.”

On the engine dyno at Advanced Engine Performance, Mark’s dreams were realised, with figures of 707hp on pump fuel and 730hp on unleaded race gas. Those are seriously impressive numbers for an aspirated, 23-degree-headed, small-block street combo with a cast intake and single 4150 carb!


We gave engine builder Pete Murray a call to get his thoughts on the combo.

“I like all my engines, but some of them I really fall in love with, and that one stands out,” Pete said. “There was a lot of R&D involved, especially in the cylinder head department. They’re a significant factor in how this engine performs, and we put a lot of time into porting the heads and intake manifold, and flow-testing the induction package as a whole.

“The main thing about this engine is it’s not an all-out race engine. For example, it’s got 12:1 compression and a custom camshaft, but it’s not a valvetrain-breaker. Mark will do quite a lot of street kays with the car, but we’re still aiming for mid-nines on race fuel with open pipes, and high nines in street trim on pump fuel.”

Horsepower Engineering
Mansfield, Qld