But they're foreign owned and designed though, aren't they? It's only the production line that's in the UK.

The people in Ford's Daganham diesel engine centre would say they're very much at the forefront of design and build in the UK.

With respect, unthrottled, for diesel engines for commercial vehicles a properly designed and matched variable geometry turbocharger surely gives better overall efficiency than a Roots blower?

I think the last one was was the Cummins NHRS which was removed from the cummins catalogue in the late sixties. I've done quite a bit of work on HD diesels, so I'm quite well aquainted as to how they are aspirated, thanks. I never claimed that a roots was a suitable device for supercharging a diesel engine.

I think the designer of this device had small displacement petrol engines in mind-where the feedback loop of the turbo is more noticeable due to the wider rev range and low rotatioinal inertia of the engine.

But the device is conceptually weak.

BTw-which turbos are designed and developed in the UK. Holset?! They were bought out by cummins years ago. Garrett and Borg Warner are the big players in automotive turbos-and have been for a long time.

Holset experimented with passenger car turbos way back but figured it was more profitable / in line with the owner's core business not to go the passenger car route.

Bet they rue that decision! Isn't it ironic that today's state of the art passenger engines are fundamentally based on 1960's truck engines? (Diesel, direct injection bowl-in-piston, HP turbocharged etc)? Formula 1 are still irrelevantly buzzing away at 19000 RPM and no one is listening.

I think they've pretty much all gone now. The turbo dominates in every game in which it is allowed to compete.

Turbos are lighter, cheaper and more reliable. Lag? Yes, there's lag but it's a price worth paying.

Audi uses a new stye 4 lobe roots in its 3.2 V6 engine. The marketing men will says its for the throttle response. In reality the engine bay isn't wide enough for the efficient placement of a turbo. Chevrolet use a similar style of blower on the ZR1 corvette for the same reason.

Mazda gave up on the twin screw compressor many years ago. MINI also switched from a blower to turbos years ago...