Electric ‘turbochargers’ are one of those why-didn’t-that-happen-before ideas we all expected to see first in sports cars.
After all, what motor most needs fine throttle response and the elimination of off-boost torque holes?
Well, Audi thinks diesel engines do. What’s more, it think diesels and electric ‘turbos’ fit together so well its demon spawn might replace the 4.2-litre V8 petrol motor in the RS5.
Which is why we drove Audi’s latest concept car, the RS5 TDI, on a Swedish circuit you’ve never heard of. Audi is so sure e-boost has legs it’ll stick a single-turbo version inside its all-new SQ7 late next year.
The RS5 TDI uses the bi-turbo 3.0-litre V6 TDI, plus an electric turbo that’s technically not a turbo. A turbocharger sticks out into the exhaust flow, which hurts it down below 3000rpm when there isn’t enough air going past.
An electric turbo doesn’t have that problem, and sits so far away from the hot bits that it doesn’t need an intercooler. The full picture adds a lithium-ion battery, a separate 48V electrical system and the 7kW electric whizzer. The package weighs 20kg all up and regenerates off the brake system.
Audi reckons 100km/h in four seconds flat, but it feels quicker than that. Why? Because while the RS5 TDI might only have 283kW to the petrol RS5’s 331kW, the V8’s relatively meagre 430Nm doesn’t turn up until 6000rpm. The TDI has 750Nm. At 1250rpm. And it uses no more fuel than a stock biturbo diesel.
That low-down grunt ends up translating to, as we found out after several side-by-side tests, the TDI concept being quicker than the RS6 Avant to about 60km/h. Easily. There’s no dialing up revs, no managing boost, it’s just stomp and go. Audi’s also cranked the artificial sound up to 11, so it’s deep and angry like an outrageously masculine, lower-revving RS6.
The RS5 TDI’s newfound throttle response also transforms the heavy chassis into something delightfully nimble, even with its extra nose weight. The sport differential helps, but so does the ability to pick up and drop revs instantly, even when the thing would normally be labouring off boost.
It settles its weight beautifully in fast corners and lets you adjust it with a precision the current RS5 can only match above 6000rpm. The chassis is unaffected by bumps mid corner, tucks its nose in and responds gleefully to mid-corner throttle adjustments.
Petrol engines will always have a place, but if this is the almost-present then hi-po mainstream petrol power might be numbered.
Engine: 2967cc V6, DOHC, 24v, twin-turbo, electric compressor
Power: 283kW @ 4200rpm
Torque: 750Nm @ 1250rpm
0-100km/h: 4.0sec (claimed)
Top Speed: 280km/h (claimed)