New TT RS proves the five-cylinder has a bright future

The new Audi TT RS looks like an increasingly competitive prospect. Just as its rival Porsche 718 Cayman falls to four cylinders, the TT RS doesn't only keep its charismatic straight-five, it gets a redesigned version of it. And more power.

The headline is a real grabber – four hundred horsepower. At least that's if you're prepared to use metric horsepower, the PS sort. In bhp, it’s an untidier 395.

But there's some underlying news that's even more interesting. The new engine really is very new. The result is lighter than the old, for better handling, and keener to rev.

It has switched from a cast-iron crankcase – albeit a rather fancy compacted vermicular cast-iron – to an aluminium one. This change saves 18kg, and actually the whole engine is 26kg lighter than the old one. New intake systems and pistons mean it's worth hanging onto the gears longer, as peak power is sustained all the way to 7000rpm. In the former TT RS and the current RS3 the five-cylinder engine tails off from 6500.

It's significant that Audi's RS division is prepared to spend money on an engine that's not used in any non-RS models. An engine that's unfashionably large, unfashionably multi-cylindered and unfashionably special.

Fashion may be swinging back its way, at least if the official fuel consumption test changes. Porsche dropped the cylinder count of the 718 series to look good in the current fuel test cycle. But it's becoming increasingly apparent that this cycle is unrealistic, and that a more relevant cycle will come into play before too many years. In a real-world test, the five-cylinder might well do okay.

We spoke to Annette Möllhof, the Ingolstadt product planner in charge of all the five-cylinder Audis – RS3, RS Q3 and TT RS. Does this engine mean the five-cylinder won't die, as many had morosely predicted? She says it has a bright future, and the Quattro division are 'actively looking' for other applications. She won't say what, but says the new engine is the same physical size and shape as the old one.

So it would seem incredible if a facelifted RS3 doesn't get this engine in due time. And probably any RS versions of the new Q2 and Q4, as well as the Q3’s replacement.

By the way, you might remember in March 2014 at the Geneva motor show, Audi unveiled a concept called the TT Quattro Sport (pictured below). Many people thought its job was to show us what the TT RS would turn out to be. It had a 420bhp four-cylinder 2.0-litre engine, and a body widened by 3cm.

TT Designer Dany Garand told Top Gear today that he would have liked the TT RS to have got the wider body, but it was too expensive. Well we didn't get that, but we did get a five-cylinder engine instead of a four.

And, sorry Mr Garand, but that seems like a more than fair swap.