07/09/2004
NEWS STORY
Renault's Denis Chevrier and Pat Symonds look at the unique challenges posed by the Autodromo Nazionale Monza... a circuit where the power is turned up to '11'.
Denis Chevrier
Monza is perhaps the definitive test of a Formula 1 engine. Although the single longest period spent at full throttle is not the highest of the year, the circuit offers an engine no respite, as it features no sequences of slow corners taken at low throttle openings. The duty cycle of the engine is the most severe of the year, with the drivers spending 70.7% of the lap at full throttle, and this produces the highest average speed of the year at around 260 kph, compared to an average of 220 kph and the slowest value of 160 kph, which is encountered at Monaco.
Indeed, this is the circuit where pure engine power has the biggest influence. The engine's maximum power is required for the longest period of any track we visit, with the driver demanding this level of performance from the engine for nearly 71% of the lap, as mentioned above. This high percentage of the lap spent at full throttle means that power has a proportionately greater role to play than on a circuit such as Monaco where the drivers use full throttle for just 40% of the lap. Conversely, though, this same nature of the circuit layout also means that the fuel effect here is relatively low, at 0.31s per ten kilos of fuel in the car.
However, Monza is not a completely one-dimensional challenge for the engine builder. The low-speed chicanes demand good driveability from the engine, and the ability to control power delivery as well as possible in order to let the drivers take the optimum line through the tight corners at Retifilo and Roggia.
Equally, the chicanes pose reliability risks in the form of the cars' passage over the severe kerbs. This subjects the entire car to sudden spikes in vertical acceleration and often sees the rear wheels lose contact with the ground. This has potential implications for engine over-revving, or hitting the limiter, and also transmission reliability. Equally, the suspension is highly loaded, and accessory components to the engine may undergo movement that can be harmful to their performance (the oil and water pumps, or the alternator, for example).
Testing last week allowed us to begin determining a number of key elements of how we will approach the race weekend, in terms of determining gearbox ratios and cooling needs. We were able to answer some of the questions usually reserved for our programmes on Friday, and Saturday morning and this may mean we make several runs fewer than is usual during these sessions. However, this does not mean we can in any sense build a 'Monza special' low mileage engine, as we need to have in hand the ability to complete these runs if necessary: a change in ambient or track conditions could lead us to run a completely normal programme, or indeed run more than usual, as we did in Spa. The only changes to the engine will be several different components in the build specification, which have been optimised firstly for reliability, but also performance.
Pat Symonds
Monza has always been known as the power circuit par excellence, and the engine is undoubtedly an extremely important element here, as the drivers spend near 71% of the lap at full throttle. But what is it about an F1 engine that makes it so special, and how does it compare to a "normal" road engine?
It goes without saying that power is all-important, and the astronomical outputs we see in F1 require the engine to turn very fast. This is because higher speeds mean the engine can ingest more air, which is vital to supporting the combustion process that produces the power. Modern F1 engines rev to approximately 19,000 rpm, while an average road engine will attain just over 6,000 rpm. The reason for these much lower speeds is that the loads imposed in the moving parts of the engine are approximately proportional to the square of its speed: for example, a piston moving at full speed would be propelled 100 metres into the air if it was unrestrained. Thus, increasing engine speed from 6,000 rpm to 19,000 rpm means loads actually increase by a factor of ten - while this is tolerable for a 750 km racing engine, it is not acceptable for a road engine which is expected to last 300,000 km.
However, when it comes to power figures, they will often be quoted without a proper understanding of their significance. Firstly, the power an engine produces is not constant, varying with ambient temperature, pressure and humidity. On a hot day, not only does the engine produce less power, but it also does so at higher rpm. This can make the testing of engines on the dyno a complex exercise, as even in an environmentally controlled chamber, the conditions are not always the same. Therefore, it becomes necessary to correct the measured power to a defined set of conditions. In road car engines, these standards are well-defined - although not the same worldwide. However, different F1 engine manufacturers use different standards, and it is therefore irrelevant, even if one knows the numbers, to quote the power of one F1 engine against another.
Indeed, while peak bhp is easy to understand and can be expressed as a single number, the true performance of the car is dependent on many other factors, not least of which is the area under the power curve. If for example an engine produced 900 bhp at 19,000 rpm but only 800 bhp at 18,000 rpm, it would be described as peaky and difficult to drive. The on-track performance would be nowhere near as good as an engine with a lower peak power of 875 bhp at 19,000 rpm, but which still produced 850 bhp 1,000 rpm below the maximum. Indeed, torque is equally important as the power of the engine, as torque is what provides the acceleration. A good racing engine, much like a road car unit, requires a generous, smooth torque curve.
The physical attributes of an F1 engine also have a role to play. Like any component on a racing car, the engine must be as light as possible, and we employ advanced materials that are both light and capable of withstanding extreme stresses. Furthermore, each component is designed for a finite life, much shorter than that of components in road car engines, and this strict lifing, as well as the well-defined usage pattern of the engine, allows the reserve factors to be much smaller as well. When a racing engine designer conceives his engine, not only does he know exactly how it will be driven, he can also guarantee that the level of maintenance will be exceptionally high - something that a road car engine designer cannot assume.
Indeed, continuing the theme of mass, it maybe surprising for some people that good fuel consumption is as important in a racing engine as a road engine. On the road, fuel consumption has a direct impact on running costs, and hence is high on the list of desirables for a prospective owner. With a racing engine, we try and carry as little fuel in the car as possible, as each litre weighs approximately 0.75 kg, and weight is the enemy of performance. Of course, the fuel consumption of an F1 car varies according to the conditions: a wet race will see lower fuel consumption than running in dry conditions. It is also dependent on factors such as the amount of rear wing being used (more wing means more drag, and higher consumption) or the grip of the tyres. While an F1 car consumes significantly more fuel per 100 km than a road engine (65l/100km compared to 8l/100 km in a road car), such a measure fails to take into account the disparity in power outputs. The specific fuel consumption, which measures the engine's efficiency in producing power, is actually very similar: 200 grammes/horsepower/hour, against 175 g/bhp/hour for a road car engine.