Writing about the demise of Saab reminded me of the sheer cleverness of the company’s engineers. Much of what the engineers did in Trollhattan never saw the light of day and a lot of what did was production work for GM. One of the most original ideas the company had was unveiled to journalists. Back in 2000 I sampled Saab’s Variable Compression ratio engine. It was a 1.6-litre, five-cylinder, supercharged unit which, roughly speaking, hinged in the middle.
This meant the upper part of the engine could be tilted by up to four degrees in relation the lower half, allowing the engine’s compression to be varied between 8:1 and 14:1 depending on the engine load.
A variable compression ratio is, perhaps, the holy grail for creating ever-more frugal engines, because a fixed ratio is compromise between all types of driving conditions. The Saab engine, though relatively crude, delivered 150bhp and 140lb ft per litre of cubic capacity, but the fuel economy of a conventional naturally-aspirated 1.6-litre petrol engine.
Saab’s engine never got any further under General Motor’s ownership and, in truth, it’s unlikely that the tilting mechanism could ever have been put into production. Achieving a variable compression ratio in a long-life production engine is very difficult, but it is the key to one of the Holy Grails of engine design. It will allow an engine to run - in certain conditions - like a frugal diesel, with the fuel/air mix igniting without needing a spark. This, in turn, will allow an engine to be much smaller for a given output and remarkably frugal.