Piston power

Roland Löwisch

We visit Stuttgart to see how Mahle, supplier of light-alloy pistons to Ferrari, fuses technology with tradition

Almost 100 years ago in a little workshop near Stuttgart two German brothers set about reinventing the piston. That firm grew into what is today a world leader: Mahle Motorsport GmbH, makers of the finest forged pistons in the world. Since the mid-1970s the Mahle guarantee of exceptional durability under extreme loads has made it the chosen supplier to Ferrari for its V8 and Formula 1 engines.

“Ferrari uses a high-rpm concept that really sets it apart from other manufacturers,” says Fred Türk, Mahle’s vice president of engineering services and motorsport. “Given the small production volumes, we can consider and develop new ideas that would normally be unthinkable due to cost.

That’s why it’s so much fun working with Ferrari." Mahle – whose components now supply every second car in the world - produces around one hundred million pistons every year, around 60,000–80,000 for Ferrari. Many Ferrari engines use regular cast technology. But most Ferrari GT models are exclusively equipped with Mahle high-strength forged pistons. Although made from the same alloys, forged pistons have a finer microstructure, with thinner walls that render them lighter. In 2018, the 488 Pista's V8 engine – the most powerful-ever Ferrari V8 - was named International Engine of the Year for the third consecutive time, as well as Best Engine of the last 20 years, a source of understandable pride for both Mahle and Ferrari.

Unlike cast pistons, where molten aluminium is poured into a mould, then solidifies, a forged piston is made by instead pre-heating a rough-cut aluminium slug and punch-pressing it into a die. The pressing is hardened by heating it to 500°C, placing it in a holding chamber, then shock-cooling it to 20°C in water to strengthen the alloy. Then is reheated to counter cracking. Secret Mahle coatings are applied to specific surface areas. Türk explains: “The most important aspects of piston production are precision, cleanliness and traceability.”

Thus, each piston receives a unique ID code in order to identify any fault-sources when it is hand-inspected, coupled with permitted tolerances equivalent to one 5,000th of a millimetre. The equivalent of one tenth the diameter of a human hair. Each cylinder bank on a Ferrari V8 uses different pistons, so each piston has a DataMatrix code to assign it to the corresponding cylinder. “We apply a chemical nickel dispersion coating to the liners to protect against friction and wear,” adds Türk. Pistons made for F1 prioritise 'knock resistance' rather than durability.

After heat-hardening, each pressing is machined on a high-speed mill (45,000rpm), then fitted with copper alloy pin bore bushings, forged in sintered stainless steel ring carriers, and receives a chemical nickel coating on the piston crown. The finished race piston is then inspected for cracks using a fluorescent dye and UV light. “As you can see, these are high-precision components,” says Türk. “They are little works of art, and we only make a few hundred of them each year.”

Road-going pistons for the V8 GT models are expected to deliver high-rpm performance for at least 200,000 kilometres. F1 pistons have instead a maximum required life of just 7,000 kilometres. Post-use analysis is essential. “They are cleaned, measured and checked for cracks and residual hardness. This enables us to identify the best cylinder in a given engine. Our task then is to bring all the other cylinders up to that level.”Effectively, Mahle and Ferrari are R&D partners. Their 2015 collaboration created a new pre-chamber ignition system to reduce F1 fuel consumption. “Today,” smiles Türk, “multiple manufacturers are using an evolution of this technology in their road-going sports cars.”