New crossover alert: it’s Infiniti’s turn to make a posh mid-sized SUV. This is the new QX50. And other than it being reasonably handsome and, from the one picture we’ve had through so far, quite brown, it’s a fairly unremarkable thing. Until, that is, you get to the engine.

The QX50 is the first Infiniti – and the first car in the world – to be sold with a variable compression ratio engine. We’ll not delve into the nitty-gritty of how internal combustion engines function because it’s almost the weekend and you probably have turkey to be Thankful for. Suffice it to say that compression ratio is the technical term for the difference in volume in an engine’s combustion chamber when the piston is at the top of its stroke to the bottom.

The higher your compression ratio, the more efficiently the engine combusts its fuel. Bad news: your engine is susceptible to ‘knock’, or ignite the fuel at the wrong moment. Which gets messy and expensive quite rapidly.

What Infiniti’s new ‘VC-Turbo’ 2.0-litre four-cylinder does is vary the compression ratio between a lowly 8:1 when you want maximum attack horsepower, and a Mazda SkyActiv-high 14:1 for ultimate efficiency. By mechanically altering the pistons’ reach, Infiniti says it’s increased fuel efficiency by up to 35 per cent versus the old QX50’s V6.