Jag reveals new engine

Fans of longitudinal engine configurations, rejoice! Jaguar has announced its most efficient powerplant yet making its debut in a prototype XF.

It is a four-cylinder diesel to the tune of 2.2-litres, and thanks to a new water-cooled turbo, low friction pistons, new injectors and a new crankshaft, is able to return some mighty impressive stats.

See more pics of the Jaguar XF development prototype

In fact, that longitudinal layout - or ‘north-south' (most four-pots are transversely positioned) - has allowed Jag's engineers to fit a new oil pan and electronic system to make the Stop-Start more efficient.

The prototype XF also debuts an ‘advanced' eight-speed auto, where the last two cogs are overdrive (good motorway cruising) coupled to what Jag claims are swift responses.

And so we come to the part where the real battle is played out: Top Trumps. And for this, we need a competitor. Step forward, the BMW 520d. The Jag's 187bhp, 332lb ft of torque, 52.3mpg and 149g/km of CO2 plays the Beemer's 184bhp, 280lb ft, 54.3mpg and 137g/km of CO2.

Jaguar claims 0-62mph in just 8.5 seconds for the 2.2-litre XF, while BMW's 520d does it in 8.1. Hmmm...

Speaking to TopGear.com, Jag told us the new engine will be available to order from April, and will arrive in September this year. Prices TBC.

UPDATE: Top Gear's Paul Horrell gives us his first impressions of the new Jag engine

On the road, the XF has mucho woosh over a nice wide torque spread, and plenty of refinement nearly all the time. Sometimes you notice the box has been programmed for obsessive economy - get stuck behind a truck at a steady 50mph and it goes for seventh, leaving the engine grumbling agriculturally at about 1200rpm. But you always over-ride with the paddles. On a motorway it's just a distant hum. And as the engine is a bag of cement lighter than the V6, it's even better in sharp corners.

As to the numbers, if you compare auto with auto (Jag gives no manual option) the BMW 520d is still a sliver more economical and speedy. But not so's you'd notice. If you like the XF, there's now no rational reason to buy a rival saloon.