John Hennessey vs Wolfgang Dürheimer: TG chats to the 300mph masterminds

Hitting 300mph in a road car. What are the challenges? Is it even achievable? The current fastest speed in a road car is 270.49mph. It’s held by a Hennessey Venom GT, only 2.63mph above the Bugatti Veyron Super Sport, and achieved in only one direction. Clearly, at these speeds, adding another 1mph is difficult, so how likely is it that their next-generation cars – the Chiron and Hennessey’s F5 project – will be able to add another 30mph to that?

Words: Ollie Marriage

Indeed, is 300mph even on their radar, or is it a step too far? At 300mph (482.8kph) 100 metres would take 0.746secs. If it happened in a stadium, you could barely turn your head fast enough to keep up. Over to Wolfgang Dürheimer (outgoing Bugatti CEO) and John Hennessey (founder of Hennessey) to tell us more…

So, Wolfgang, what would you say are the main challenges of going very fast in road cars?

Well, when you are out to break new ground in an area where nobody was so far, you cannot 100 per cent predict the problems you will face. But it starts with the tyres, because at that speed you have a stress load on the tyres, especially on the surface, that is immense. Once again, we are working with Michelin – I think we are their most challenging tyre-development partner – but in the whole of Europe, we did not find a test bench to cope in terms of durability and high-speed capability.

We actually found a bench in the US that is used for aircraft tyres, and it’s been used to extremes to make sure the tyres are stable enough.

Click here to watch Chris Harris drive the Bugatti Chiron

After tyres comes aerodynamics?

At high speeds, aerodynamics and power are very closely related. To go fast, you need the power of the engine to break the barrier and to compensate for the aero drag you build up – it’s like moving a bookshelf through the air. Aerodynamics on the Chiron took all the computational power we had in the Volkswagen Group, because when you approach 400kph, life, in driving dynamic terms, gets very demanding, and it takes a lot of effort to develop the aerodynamic balance so the car is predictable and safe in all circumstances.

Can you model everything on computers?

Not everything. When you are at these limits, pushing the boundaries, you don’t know what you might find, so it’s important not just to look at computers, but to drive and test the car. Let me give you one example. We were in South Africa to do high-speed tests with the car in its final design, and we realised when we went at very high speeds for a longer period of time the single-beam lightbar and carbon-fibre parts at the rear started melting due to the extraordinary exhaust heat – approximately 1,000 degrees Celcius when it comes out of the pipes.

So we had to develop an air duct on the outside of the exhaust that ejects the hot gas out about 80cm further behind the car, and then it was fine.

The pressure within the engine must be huge?

It was quite a challenge to add 50 per cent on top of the Veyron’s 1,000 horsepower from the same displacement. To go 400, don’t start below a thousand horsepower and to go, let’s say, 450, don’t start below 1,500bhp. You will not make it. There are thousands of pieces in this engine, and they all need to sustain the stress load – we have to bring one cubic metre of air per second through the combustion chamber and out again. But we knew we needed this power to approach the 450kph limit.

When we went at very high speeds for a longer period of time the single-beam lightbar and carbon-fibre parts at the rear started melting due to the extraordinary exhaust heat

450kph is 280mph. Are you intending to go for a bigger speed than 261mph in the standard car?

While the car will remain limited at 420kph [261mph] for public roads, we will try to do another world speed record for street-legal cars most likely in 2018. This will happen under controlled conditions on our test track.

And 450 is an achievable target? 

It could be possible, but we don’t know yet, we are still testing.

Are you looking beyond that as well? Or is that the line in the sand?

Nobody draws a line in the sand, I think the race goes on, and when someone crashes the 450 barrier, someone will try 451 a year later. But in this game, you cannot predict what is going to happen. You have to be careful, control the conditions, have the right air, wind, road conditions. But this is what we like to do, and it’s the big factor of differentiation in Bugatti, that we do this and tell our customers what the cars are capable of.

Top speed still sells, then? 

Power, speed and lap times are what sells.

But the Chiron isn’t a lap-time car… 

No, but the car has its own rules, and on a track like Le Mans where we have an ultra-long straight, this is the El Dorado for a Bugatti. Fast and long turns are our domain.

How much does being first matter? How important is it to have a rival?

Of course it’s good to have competition. To only beat yourself is not what we are looking for. But is it important for us to be number one? It’s ultimately important for us, because we are representing our customers, and our customers are number one wherever they show up. I always say if you come in second you are the first loser.

Will you do the high-speed runs at Ehra? 

Ehra is a playground for us – it’s like heaven. We have the ultimate straight and predictable conditions – we know what the wind’s doing, and the track is right in front of our door.

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