Bentley’s Continental GT3 Pikes Peak did pretty well at this year’s Hill Climb, managing to come in second in Time Attack 1 and fourth place overall. The machine was the best performing among the renewably-powered cars. Bentley claims it did so well, its run would have been record-breaking — if not for the closures that stopped the cars from safely finishing the last third of the climb.
The Continental GT3 produced 850 horsepower at altitude, which would be something around 1100 HP at sea level. Getting that much power took a lot of collaboration between Bentley and its motorsport partners. Their work is broken down in a detailed report from Racecar Engineering (RE), who cite Bentley’s Technical manager of Motorsport Engineering, David Argent.
It’s clear in the report that Argent and Rhys Millen, the GT3's driver at Pikes Peak, were competing not just with other race cars, but with the Peak itself:
Specifically, it’s the altitude that the GT3 was fighting as its 4.0-liter, twin-turbo V8 pushed up the mountain. Fans of the Pike Peak Hill Climb already know how the elevation affects the machines, but the report from RE explains how Bentley got its turbos to work efficiently at altitudes ranging from 9,390 to 14,115 feet.
Argent explained that it’s all about the turbo wastegate:
‘One of the first things we found out when we were out at the Pikes Peak is that the wastegate control we selected when we’re at sea level wouldn’t allow us to meet those boost targets even with the wastegates fully shut,’ notes Argent. ‘We did some optimisation to get the right size turbo housing to allow us to have the response and meet our boost targets. We had to go to an external wastegate because the internal wastegate wasn’t big enough to dump what we needed to control the boost.’ The ratio of compression from atmospheric pressure to turbo pressure is peaking at 3.7.
Going from about 525 to 850 HP (at altitude) didn’t just need better airflow.
It also required a beefier fuel system, which the Continental GT3 got by adding port injection to its direct injection, according to Argent:
‘We sourced appropriate injectors and fuel rails. The injector size and flow were based on the power figure we want to achieve at the bottom of the run at 9,390 ft above sea level. We added port injection to work with the direct injection that already existed on the engine to achieve the volume of fuel we needed to generate the power we wanted and had to work out how we could achieve the power figure in controlling both injector types.
As if the altitude and power targets didn’t make things hard enough, the Bentley also ran on a renewable fuel.
The renewable fuel complicated things, a bit as the report detailed:
Bentley has been working with Esso’s renewable racing fuel for this project – a blend developed from bio content with an ethanol base equivalent to an E85. The characteristics of the fuel meant the engine required little work in calibration to operate on it, despite it being a more volatile mixture than the traditional race gasoline used in the GT3. There are no additives to the fuel blend to aid oxygenation of the combustion fluids to compensate for the reducing are density as the car climbs Pikes Peak.
With the increase of power and chaos in the fuel and air mixture, Bentley had to be careful to ensure that they didn’t reach the knock limits of the mix before the desired ignition timing.
Again, the team used bigger turbochargers to address the lack of air density and the fuel mixture, per the report:
‘We had to get more air into the engine to coincide with fuel, so we also went for bigger turbochargers with appropriately sized compressors and turbines,’ says Argent. ‘Consequently, we have turbos with a large compressor and a significantly small turbine to compress that less dense air and get the least turbo lag possible.
But I think the coolest part is Argent explaining how it’s not fully outright power that makes for the best car at Pikes Peak, because somewhere along the way all that power can become useless:
‘At a certain point, you will get traction limited,’ highlights Argent. ‘You can’t just stick a thousand horsepower and 1400 newtons to torque through a rear-wheel-drive because you won’t be able to use it. We looked at suggested figures from Rhys and some simple simulations with inside Bentley to suggest what power figures we should target.’
Getting as close to that intersection of usable power and traction — but not beyond — is what gets the car up the mountain faster. Bentley was happy enough with its performance, it hinted that it might be back for more next year.