Trying to find any substantial information about Australian Pro Stock racing on the Internet is like trying to get your kid to eat Brussels sprouts – simply speaking, it’s tough! Seeing the video of this Aussie Pro Stock 400ci SBC engine from Patterson Racing singing on their dyno takes your author’s mind back to the small-block Pro Stock Truck class and their high revving 358 inch engines that departed NHRA competition just over a decade ago.
Patterson Racing has been in business for 35 years and is widely known for their cutting edge engines and innovations in the racing arena. Naturally aspirated small blocks like the ones used in the Australian National Drag Racing Association‘s Pro Stock field are close to their heart. The typical engine puts out over 2.75 horsepower per cubic inch without any power adders and they spin at over 10,500 rpms. When compared to the NHRA Pro Stock engine of the 500-inch variety the little ANDRA version is not as tightly regulated in terms of rule restrictions on modification.
As engines for competition are typically closely-guarded secrets, we were only able to obtain a few images – and no close-ups of the internals. However, we did obtain the privilege to speak to Todd Patterson about the technology that goes into one of these technological wonders.
“Internal engine mods are wide open,” said Patterson.
Most start with a Dart Iron Eagle steel block to keep engine sealing to a maximum as opposed to being concerned with weight and opting for an aluminum block. 4.200-inch bores are common but the blocks must maintain the stock small-block 4.400-inch bore spacing, which leaves very minimal room between cylinders.
There is no block filler used to solidify the block, Patterson says that can lead to other issues such as irregular cylinder distortion due to temperature differences between the areas that are filled and those surrounded by coolant.
The decks of the Dart block are prepared to a near-mirror finish, designed to provide the perfect mating surface for the multi-layer steel gaskets to contain the combustion – the same finish is applied to the cylinder head deck surfaces. Patterson uses Total Seal low tension .6mm rings – approximately .023-inch – which are given a diamond finish from the manufacturer to make sure they are as flat as possible and then coated to prevent binding in the tight ring grooves. Speaking of diamonds, Diamond pistons are tasked with filling the huge bores and a short stroke of around 3.500-inch-3.570-inch helps achieve an approximate and optimum 1.68 rod to stroke ratio.
For GM based engines such as seen here, there are two cylinder heads of choice; a cast SBX head from CFE, or billet aluminum heads with no limit as to what goes on inside them. Valve size is critical as well so that the flow into the cylinders isn’t hindered.
“Most guys run Jesel valvetrain with .937-inch keyed lifters and the biggest wheel offered, and at least a 60mm cam journal with well over 1-inch of intake valve lift,” says Patterson.
PAC or PSI springs keep the valves on their seats but are cycled out frequently due to the extreme nature of their operation. Push rods the size of your pinky are stuffed into the lifters to prevent as much deflection as possible and to keep all 400 inches screaming for just under 7 seconds in the ¼ mile.
On the top side of the block, CNC billet intakes are the norm and competitors are permitted to run split Dominators. However, Patterson says most use a pair of standard Dominator carburetors with throttle bore sizing and booster signal optimized for each engine.
He also explains that it’s important for the racer to stay on top of the tune-up from the dyno here to when it is actually raced on track over there. The Aussies are allowed to use oxygenated fuel and there is not a spec fuel as there is here in NHRA competition. “The racers gravitate to the trick fuel of the week,” he says, meaning that a significant increase in power can be obtained based on the fuel blend. This blend can change frequently and isn’t available here in the States when the engine is broken in on the dyno.
Oxygenated fuel is great for power, but can lead to another call to the piston supplier if it’s not properly introduced into the combustion chamber. You have to admit though that it’s worth the risk when the end results sounds like this!