Out of the Box

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POSTED ON October 30, 2017

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.


On Dyno.
After assembly the engine was fitted to the Superflow 902 engine dyno at C&R Motorsport Developments, where it was subjected to a break-in process to bed the rings and settle the vavletrain. After a quick oil and filter change and a once-over, it was time to open the throttle all the way. The first set of runs were carried out with 98-octane unleaded in the tank to see exactly what this engine was capable of in true street trim. The results were surprising. between 5050rpm and 7550rpm the motor averaged 653.8hp and 548.5lbs/ft of torque. The peak number of 700.5hp at 7100rpm was a very strong result, showing 1.67hp per cubic-inch on pump fuel. The real clincher for any street engine is torque because it often has to shift over 3500lbs of lumbering mass and not a svelte 2300-pound race car. Peak torque was quite staggering at593lbs/ft at 5050rpm, while the average between 5050rpm and 7550rpm was 478.6lbs/ft. Any street car that produces just under 600lbs/ft of torque should not be messed with – just smile politely, keep your eyes straight ahead and pull away slowly. Many racers these days have dedicated fuel cells or even complete fuel systems for the race track – separate from their main fuel tank for daily duties. For that reason, Leon decided to test the mighty 420 with some VP109, high octane racing fuel, just to see if he could alter the tune to suit and coax a few more horsepower out of this recently acclaimed Allstar. The engine responded instantly to the race fuel and the numbers were up everywhere. Peak power rocketed to 714.5hp at 7050rpm – an instant gain of 14hp, which is no easy feat from an efficient engine already making 700hp. As expected, the average was up 12.8hp across the same 2500rpm sample set. With the VP109 aboard, the peak torque number smashed through the 600 barrier with 605.5lbs/ft at 5050rpm. Again, the average was up by 10.7lbs/ft across the test range.

420 Chev Dyno Data 98 Unleaded Fuel
420 Chev Dyno Data VP 109 Fuel


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