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It's not often that we see a major change in the architecture of an engine. Detail changes over the years, yes: four valves per cylinder, turbocharging and variable valve-timing, once exotic, have all become commonplace over the last quarter-century. But no-one has tried to vary the compression ratio, the amount by which the fuel-air mix is squeezed as the piston reaches the top of its compression stroke. Until now.
Saab, the company that made the turbo engine a mass-production reality, is behind a new idea that can cut fuel consumption by up to 30 per cent compared with existing engines of similar power. By allowing the compression ratio to vary between 8:1 and 14:1 - a normal modern engine is typically about 10:1 - Saab can run the forced induction that it always likes to use at much greater boost pressures, so forcing in more fuel-air mixture, while also letting the engine run much more efficiently when it's not working hard and the turbo isn't boosting.
The result is an engine that can deliver huge amounts of power and torque from a small cylinder capacity. From its 1598 cc, the prototype Saab Variable Compression (SVC) engine delivers 225 bhp and the same amount of torque (pulling power) in lb ft, while returning better fuel consumption than existing similarly-powerful engines. It shows that the more that an engine's parameters can be altered to suit different types of driving, the more efficient it can be for more of the time. The lower friction levels of a small engine help, too.
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