Formula 1's turbo eras compared

Expensive. Unruly. Spectacular. Turbocharged engines in Formula 1 are nothing new, but until this season they were banished from the pinnacle of the sport for a quarter of a century.

We have since seen V12, V10 and V8 configurations of normally aspirated propulsion, but now turbos are back - helping to drive F1's new generation of socially responsible, energy-efficient, hybrid V6-engined cars.

Their return has inevitably drawn comparison with that bygone era of flame-belching, tankslapping, 1000bhp-plus qualifying specials. But the drive for efficiency demanded by the latest regulations in F1 means today's turbo engines are very different to their forebears.

"The fundamental difference is that everything on these power units is geared to fuel efficiency," explains Rob White, deputy managing director (technical) of Renault, which was the first manufacturer to develop turbocharged engines for F1, and supplies the Red Bull, Toro Rosso, Lotus and Caterham outfits with its latest powerplants today.

"The similarities of course are that we have a turbocharged, V6, twin-cam engine as a structural part of the car. The differences are principally the additional electrical stuff.

"The internal combustion (IC) engine is worth around about 600 horsepower, the MGU-K (energy-recovery system) is worth around about 160 horsepower, and of course the performance delivered to the car is all about delivering the maximum amount of IC engine power and complementing it with the maximum amount of electrical power.

"That is where the management of energy becomes so crucial. We're harvesting energy during braking using the MGU-K, and harvesting it all of the time the engine is running using the MGU-H [a component of the turbo]"

The latest Renault F1 turbo has little in common with its predecessor © XPB

The MGU-K is a motor generator that is mechanically coupled to the engine's crankshaft. When used as a motor, the crankshaft is driven and the car is accelerated. When used as a generator (under braking), it brakes the transmission to the back wheels and slows the car down.

While the car is braking, rather than dissipating its kinetic energy as heat evacuated from the discs and pads, part of the energy is recovered as electrical energy, which is either stored in the battery or used to drive the other electrical machine on the turbo.

The MGU-H is another electric motor generator on the engine, directly coupled to the shaft of the turbo. The turbo essentially performs dual functions on modern F1 engines: compressing the intake air to the engine for combustion, and recovering heat energy from the exhaust to convert into electrical energy. That energy can either charge the battery or be used to directly drive the MGU-K. Simple, huh?!

"A simple way to think about it is what we call turbo compounding, where additional power from the exhaust turbine is converted into electricity to feed the MGU-K and used to propel the car," explains White.

"That's a concept that is not unique to F1. With a mechanical transmission it's used in trucks, road trains in Australia, long-distance trucks in America. It was used in bombers in the Second World War. What's different for us is that this is just one of many modes that we can use."

The need to harvest energy under braking with these new engines has led to the introduction of brake-by-wire systems on the cars. These balance how much work the MGU-K does in slowing the car down with that performed by the conventional disc-and-caliper brakes.

"If you want to slow the car down then either you apply the brakes or you lift off the gas," explains White. "When you lift off the gas, why does the car slow down? Because the friction in the engine brakes the input shaft to the gearbox that is connected to the rear wheels.

"With that exact same concept in mind, if we use the MGU-K as a generator, that will brake the input shaft to the gearbox and slow the car down. How is drive-by-wire related? Because that's not sufficient to slow the car down. The brakes need to work at the same time, and brake-by-wire is the arbitration between the two sources of braking torque: the electrical generator, which is fixed to the engine, and the hydraulic actuators to the disc callipers that are attached to the uprights that are connected to the wheels.

Grosjean had chance to try the 1983 Renault

"The tricky thing is that the driver doesn't know, or need to know, which one is doing the work. So that needs to be dealt with automatically. The contribution of the MGU-K is significant and now the rear brakes are dimensioned assuming that the MGU-K is present and working. So the rear brakes are under-sized to a car without K recovery."

This explains why Lewis Hamilton suffered rear-brake failure when his Mercedes lost the use of its ERS in the Canadian Grand Prix. According to White, nothing should change in terms of what the driver feels when he hits the pedal, but the rear brakes have become smaller. He suggests the reason we've seen more drivers locking up under braking this season has more to do with the lack of downforce on the cars than braking-by-wire.

"The control system reduces the hydraulic work done at the rear wheels while the electrical system is operating," adds White. "The driver needs to have confidence in his braking and feel the same thing. If the battery finishes up being charged halfway through braking, you need to be able to stop charging the battery so it doesn't explode.

"But you can't turn off the braking contribution made by that without doing something at the back of the car, so this is [why we have] brake-by-wire."

That explains why slowing the cars down has become more complicated, but what about driving them forwards? Fuel was a key component of the previous turbo era, as engine manufacturers strove to extract more horses from their stables (before the rule-makers began reining them in). The same is true now, though the focus is slightly different.

"Our task is to make the very most out of every single molecule of fuel," says White. "That's why the fuel-flow limit [of 100kg per hour] is such an important thing.

"We seek to use every available drop. There's no boost limit so we use the exactly calibrated correct amount of air to match the fuel, so once we've burnt the fuel then we use the systems on the car to recover as much energy as we can.

Jean-Pierre Jabouille handled the early years of Renault's original F1 turbo work © LAT

"The big difference between the original turbo engines and the modern engines is the optimisation, which is completely about maximising the performance with an extremely difficult fuel-consumption constraint. It's a different optimisation target, but fuel development was absolutely at the heart of progress in the previous turbo era."

One of the biggest talking points surrounding this latest generation of F1 engines is the noise (or rather lack of) they produce compared to the V8s used until the end of last season. White is talking to AUTOSPORT as Lotus-Renault driver Romain Grosjean samples the turbocharged Renault RE40 that nearly carried Alain Prost to the 1983 world championship. We have to pause as Grosjean flies past the pits because of the rasping sound it makes, so the natural question is why are the new turbo engines so much quieter than their predecessors?

"One thing is that the 1980s car has four exhaust outlets, the new cars have one," explains White. "Next thing, the '83 car is probably 20-something per cent efficient overall and one of our cars now is 40-something per cent efficient. The wastegates that feed two of those '80s exhaust outlets are open a lot more of the time than now, because we prefer to have the wastegate closed and harvest the energy.

"That old Renault sounds a bit louder than this year's cars, and honestly a little bit nastier. It doesn't run as cleanly, it doesn't accelerate as crisply, it doesn't shift gears as well, but fundamentally it's a similar type of noise."

The return of turbo engines amid a significant technical overhaul of F1 prompted much speculation that fans would see a return to the days when engines regularly blew up spectacularly during races. It hasn't quite worked out that way, mainly - reckons White - because the whole way F1 works has developed so strongly.

"The regulations [then] permitted freedom we don't have now," adds White. "Everybody hears talk of more than a 1000 horsepower in qualifying, or power output that you couldn't measure, but even then in racing trim there were different constraints.

"Of course the whole framework of F1 was different. With the available resources, the teams at the time did a fantastic job, but F1 has moved on since the previous turbo era with the big guns of major car manufacturers slugging it out, and really reliability has improved mainly because it's become so important to be reliable.

"To be nearly reliable, but not quite, is not the same thing as being reliable. The number of individual parts is immense - there are 5000 individual parts in a power unit now.

"It's nobody's intention to avoid the spectacle of big fiery blow-ups, or cars breaking down on the last lap. I would say it is fundamentally just due to the way in which all of F1 has moved on, and become so much more professional."