WA’s own crate 420 Chev crate engine hits 700hp on dyno running 98-octane fuel
This engine is the latest instalment in a line of crate engines that have been in development at A1 Hi Performance in Myaree. In most cases a 700hp smallblock is classed as a bracket engine but this particular motor has such a good idle and such excellent throttle response that it would suit a weekend warrior perfectly. This motor would make it possible to drive your Torana, for example, down to the Motorplex, bolt on some slicks, fire off a quick 9-second pass and then amble home again.
Leon from A1 wanted to show that it was possible to build an engine that ticked all the boxes and could go past 700hp at the same time. To do so meant examining every area inside the engine that could be improved – even slightly – to increase the available horsepower at the back of the crank.
First and foremost was to take up good friend Tony Bischoff from BES in the US, a regular Engine Masters contender, on his offer to supply a set of 18° Dart Pro 1 cylinder heads for the engine. These remarkable pieces flow 375cfm of air at 700-thou through the intakes and 270cfm through the exhausts, which puts them in the 800hp realm in a high compression engine, straight off the bat. The Darts run 2.18 and 1.60-inch valves and are of a spread-port design, which separates the to centre exhaust ports in order to keep those ports cooler by preventing them from sharing each other’s heat. Leon takes this a step further by plumbing in a special external transfer line from the water jacket between the ports to the outlets of the water pump. A further internal water pump modification forces water to pass through the heads rather than favouring the path of least resistance through the block. Even cylinder temperatures lead to greater power production and less opportunity for detonation.
A Dart SHP block was torque plate honed, line honed and machined to achieve zero deck height before the rotating assembly was installed. 420 cubic-inches are achieved with a 4.155-inch bore and a 3.875-inch stroke. It pays to keep in mind in this modern age that not so long ago 420-odd cubes was the realm of big blocks only and that big blocks needed big port heads, big manifolds and big carburettors to unleash their stump-pulling potential. Well guess what? Times have changed but the laws of physics haven’t. Just because we can now build a smallblock with big block displacement, it doesn’t mean we can run typical smallblock heads, manifolds and camshafts and expect to come out all grins and giggles when the engine hits the dyno. Big enignes need to be treated as such to achieve the best results and that is part or the reason behind this engine’s success. It may have 12:1 compression and that may sound high for a 98-octane diet but consider the camshaft timing, the efficiency of the combustion chamber, the cooling system modifications and a host of other improvements and you will begin to piece the puzzle together for yourself. When everything works in harmony: everything works.
| A: This coolant bypass hose allows hot water to escape between the two centre exhaust ports, making the cylinder head temperatures more even from cylinder to cylinder.
B and C: A view inside the valley reveals the specially milled baffle that prevents oil from running back onto the camshaft – again reducing frictional losses.
D: The two kick-outs in the sump allow oil to be thrown outwards and away from the rotating assembly to dramatically reduce windage drag.