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.
Mercedes have been working on the idea for years. BMW’s most senior engine designer told me in 2010 that the they had the engine ‘running well’ on the test bed, but that the leap to production reality was a large one.
However, an independent French company, MCE-5 Development, partly backed by the French Government and the EU, has come up with a brilliant solution to creating a variable compression ratio engine by, in rough terms, pivoting the middle of the conrod and then moving the pivot point. Thanks to some brilliantly original engineering, it can continuously alter the compression ratio of each cylinder, in fine increments, almost instantaneously.
MCE-5’s 1.5-litre, two-stage turbo, prototype petrol engine is good for 215bhp, 332lb ft of torque and 122g/km, with more to come. I’d love to see it in a car, but will any mass-maker be brave enough to ignore ‘not-invented-here’ syndrome and buy-in this technology? Maybe this is the kind of home-grown technical leap forward that would help Renault leave its current malaise behind.