When you buy any Mégane R.S., you know Renault Sport’s engineering history and reputation can be trusted to bring your dreams to life. Behind that promise is an intensive process that tunes and tests the engine performance...
Sébastien Norie, Powertrain Driveability & Performance Feeling Lead Engineer for Renault Sport Cars, is one of those responsible for delivering a final product the company can stand behind. He describes the development process.
“First we tune the engine by itself on a test bed,” he says. “By the end of that, we are very confident we have matched its maximum power and torque by taking into account the reliability of all its mechanical parts. Then we put the first prototypes in the cars, to do all the fine tuning.”
Power and torque may sound like dry measurements but they are far from that. Power is a headline figure for any engine, but torque is sometimes even more important. “Low-end torque” is what gives a car its zip out of corners or off the start grid.
You need a good balance between torque and power
“If you have a lot of torque but no power, you will have plenty of acceleration at low rpm, but none at high rpm. The opposite is also not what we are looking for…
“Indeed, the shape of the power/torque curve is very important. The balance of the two gives you the “fun to drive” feeling. We talk about that and the “high rpm” feeling, which are what we expect from a sports car.”
Sébastien warns against the temptation to look for more power. “There are companies out there who promise to retune your car for more power,” he says. ”But we know that if they do that they are compromising things like durability or efficiency under all conditions, including everyday sporty driving and track usage.
“For example, we test the car in France on test tracks and open roads, but also in very extreme conditions: in Sweden, where it is very cold, and the south of Spain, where it is very hot, and also at altitude.”
As well as on the road, any car under development is also extensively tested on a rolling road, or “dyno” (short for dynamometer). This is a set of rollers where power and torque can be measured by sophisticated instruments under consistently replicable conditions. It may seem straightforward but every detail has to be carefully monitored to ensure accurate results.
The first step is to secure the car safely in place, while ensuring the forces applied to it by those restraints do not affect its dynamics, for example by compressing the tyres too much on the rollers. Exhaust extraction also has to be efficient enough not to add any back-pressure that might affect the power readings.
The engine is then run up to speed for approximately 15 mins until both engine and gearbox have reached their proper operating temperature.
A large fan is set to simulate the effect of the slipstream, varying directly in line with the car’s speed to allow both turbocharger and engine control system to work properly. The roller speed can also be controlled to increase the load on the engine and help raise its temperature.
“After running at high speed in fourth gear, you go into neutral and decelerate down to low speed,” says Sébastien. “This coastdown measurement – of the loss of power from the friction of the gearbox, differential driveshafts and wheels – is done three times to check the repeatability.
“You then do a full load acceleration in fourth gear, going from low rpm up to the engine’s maximum. Measuring the power at the wheel, and adjusting from the coastdown measurement, gives us the real power of the engine.”
The full-load test is repeated several times and the testing finishes with another three coastdowns to check that measurement again.
This precise rolling road testing is only part of the intensive work that goes into maximising the efficiency of your Mégane R.S. All these tests are carried out on more than one car, to check there is no difference on the production line.
As well as testing the Mégane R.S. – and all its other cars – at every stage of the development process, Renault also employs an external test company. This uses a series of tests that are standard across the Automotive industry, allowing for a legitimate comparison of the results.
“This leaves us very confident of the figures we give for the Mégane R.S.,” says Sébastien.
The end result is every Mégane R.S. owner can be absolutely sure that their car is correctly operating at peak power, peak torque, peak efficiency – and peak fun.