How Porsche 3D Printed Pistons for the 911 GT2 RS

Porsche’s 3D printed pistons are the clearest case yet of additive manufacturing improving an engine that had already been optimised for decades. In 2020 Porsche, working with Mahle and Trumpf, printed pistons for the 700 PS engine of the 911 GT2 RS that were about 10 % lighter than the forged production pistons and carried a cooling duct inside the crown that no forging or machining process could make. The result on the test bench was up to 30 PS more from the same engine, and pistons that ran cooler under the highest loads. This is what they did, why it worked, and what it means for everyone who does not make supercars.

The problem: a piston that was already as good as forging allows

A piston lives in the worst place in a car. It is accelerated and stopped thousands of times a minute, its crown faces combustion at well over 2,000 °C, and every gram of it has to be carried by the connecting rod, the crankshaft and the bearings. Engine designers spend careers shaving mass from pistons and getting heat out of them, and the forged aluminium piston in a modern high-performance engine is close to the limit of what forging and machining can do.

Two constraints hold it there. A forged piston is solid where it does not need to be, because a forging die cannot leave a void inside a part. And its cooling is limited to an oil-spray gallery on the underside, because a machined channel cannot follow a curve inside the crown.

What was printed, and how

The GT2 RS pistons were built by laser metal fusion, the powder-bed process in which a laser melts metal powder layer by layer. The powder was a high-strength aluminium alloy developed by Mahle for the job; the machine and process came from Trumpf; and Zeiss measured the finished pistons to confirm that the printed geometry matched the design.

Two things changed in the design because it was printed rather than forged.

• Material only where the load goes. The piston’s structure was derived from its load paths, with material removed from lightly loaded regions. The printed piston weighs about 10 % less than the forged part it replaces.
• A cooling duct inside the crown. An integrated channel in the piston crown, close to the ring zone, carries oil where the piston runs hottest. The ring zone in the printed piston runs measurably cooler, which is what lets the engine make more power without the piston failing first.

Porsche fitted six of the printed pistons in a GT2 RS engine and ran 200 hours of endurance testing, including around 135 hours at full load, and reported up to 30 PS more from the 700 PS engine with improved efficiency. Porsche’s own account is on its newsroom.

Why this matters beyond Porsche

It is easy to file this under “things a supercar company can afford”, and the metal printing of a piston is indeed expensive. The lesson is in the design, not the budget, and it transfers.

• The gain came from geometry the process allowed. Nothing about the alloy or the engine changed. The piston got lighter and cooler because printing let the designers put material and a channel exactly where physics wanted them. Every part designed for a mould or a forging carries the compromises of that process, and a surprising number of them can be removed once the process constraint goes.
• Lighter parts improve the parts around them. A lighter piston is a lighter connecting rod, a smaller counterweight, a lower bearing load. In a drone airframe or a robot gripper the same chain runs: a gram at the tip is worth more than a gram anywhere else.
• Internal channels are the printable feature. Cooling channels in a mould insert, a manifold consolidated into one part, a duct that follows the space available: these are polymer jobs as often as metal ones, and they are the geometry we see most on our own floor. Our design for 3D printing page is largely about how to exploit them.

What it does not mean

It does not mean printed pistons are coming to production cars soon. Metal powder-bed printing is slow and expensive per part, and a printed piston is qualified through the same years of durability testing as any other engine component. Porsche made these for the GT2 RS, a limited-run car, and as a research programme. For most automotive work, printing pays in the polymer parts, the tooling and the small runs we describe in our automotive article, and the process guide is candid about where metal earns its cost.

Designing a part around what printing allows

The useful question the Porsche piston asks is simpler than it looks: which of your parts is the shape it is because of how it is made, rather than what it does? A bracket that is a solid block because a machine shop quoted it that way; a duct in three pieces because a mould could not release it in one; a housing with the cooling on the outside because the inside was unreachable. Those are the candidates. Send one through the quote page with a note on what it does, and our engineer will tell you what changes when it is printed.