The Starfire was Australia's first locally designed and developed 4 cylinder engine.
Australia's First Locally Designed and Developed 4 Cylinder
Holden's Starfire 4 has come in for its fair share of criticism. Some justified – and some a little short sighted. What people these days tend to forget is that the Starfire 4 was not only GMH's first - but Australia's first - locally conceived, designed, developed and produced four cylinder engine. It was in 1972 that initial thoughts were directed at the production of a four cylinder engine by GMH, the actual commitment to go ahead coming in 1975.
Early Research and Development units were six cylinder 3300cc motors fitted with a special crankshaft and other gear, using just four of the cylinders. Performance at that time was not acceptable as rpm's available were too low. Torque is important in small engines, perhaps more so than top end power as far as driveability is concerned, for which reason considerable redesign became necessary.
Besides, it was determined from the earliest stages that total compatibility as far as noise and vibration were concerned, was essential when fitted to a vehicle. The "Astron" style of engine was considered, but was discounted on grounds of complication and expense. Instead it was decided to go for total conventionality, but using all the resources of the latest technology.
Up to the end of 1976 the Bendix single choke carburettor was to be fitted, but a re-establishment of objectives meant that GMH settled on the Strasbourg Varajet, along with the inevitable delays that accompanied the choice. Complex overhead-cam systems, as well as aluminium construction, were dismissed early in the piece. The former offered few real advantages in this, a purely street engine with no pretentions of a problem with OHC arrangements.
On the matter of aluminium, corrosion from the high salt content of water in many parts of Australia helped the designers decide against its use. It had been observed that many aluminium engines suffered from this severe corrosion problem without providing any real benefits to offset the situation. Even in terms of weight, many aluminium units gained little advantages as extra stressing was often necessary for rigidity.
The New Varajet Carburettor
The gestation period extended slightly by the long lines of communication between Fishermans Bend and the Strasbourg based manufacturers of the new Varajet carburettor, brought the new engine's announcement perilously close to the debut of the new Holden VB Commodore, but they made it in time. Based on the 2850cc six cylinder in terms of cylinder dimensions and many working parts, the "L 18" motor was nevertheless a completely new design. Around 56% of the components, a total of 383 parts to be precise, were common with the L 6, but this was a very real advantage in terms of production economies of scale, as well as subsequent maintenance and repair. GMH engineers believed the engine had a normal life of at least 100,000 kilometres between rebuilds – but owners have told us they got many more than that.
As important as the engine's actual design was the fact that, as installed on the Sunbird SL/E, a total integration program was completed to ensure the complete compatibility of the power unit, transmission and drive-train, plus body/chassis unit. With 60 kW (approx 80 bhp DIN) of power and 140 Nm (113 ft lbs) of torque, compared with the Opel OHC engines 72 kW SAE (96.5 bhp SAE) and 115 lbs. the Starfire was a little down on power. The L18 featured an iron head with pushrod overhead valves, and an iron block, these parts being specific to the Starfire and NOT cut down versions of the old six.
Eight ports were used in the head, the valves being chrome stemmed with aluminised tulip heads. The exhaust valves (36mm), had positive rotator caps. Inlet valve diameter was 41mm. Valve guides were recessed and operation was through hydraulic lifters, driven by a computer designed camshaft. The valve springs had flattened inner damper springs to prevent bounce and clatter. Long reach spark plugs took the ignition nearer to the centre of the swirling mixture in the combustion chamber which was of fast burn design. The compression ratio was 8.7:1. The cast iron block featured five main bearings of premium tri metal type.
The pistons were straight from the 2850, but connecting rods were specially designed. There was a horizontal baffle and scraper system in the sump to prevent oil starvation and the PCV system was tuned to the engine's specification. Possibly one of the most interesting features of the Starfire was its carburettor. Based on Rochester design, the Varajet was from Strasbourg, and was initially intended to make its debut on the new engine. But by the time the Starfire was being fitted to the Sunbird it had already been deployed on the Opel engine in Germany.
A two stage progressive instrument, the Varajet had a 35mm primary choke to encourage good fuel preparation and to assist economy as well as emission control, plus a 46mm secondary choke to allow good breathing in the top end of the power range. The breathing capacity of the Varajet was twice that necessary for the engine, equalling the performance of Rochester's Quadra-jet. For ease of starting there was an electric choke with two stage heating element to avoid initial over enrichment of the mixture when cold. There was also pre-heating of air supplied to the carburettor. There were four individual inlet port runners with a tuned control plenum chamber, all cast in aluminium. The cast iron exhaust manifold had dual outlets to accommodate twin downpipes.
Weighing 18 kilograms LESS than the Opel engine, the Starfire 1892cc engine could be "shrunk" to around 1400cc, or expanded to a maximum of 2200cc as used in the MHDT rally Gemini. It also had 7 per cent better economy according to tests conducted by the factory. The Starfire proved to be a very flexible power source that would pull well from 2600 rpm and rev out to 6400 rpm. Provided you drove gently the Starfire would happily pull from around 1500 rpm with gentle throttle usage.