Interesting new choice. The text below, taken from an Engine Builders article, with most of the info from a Mahle engineer, discusses the pros and cons of 4032 vs 2618. It does sound like 4032 is a better choice for most Commando builds, as long as you're not running forced induction, nitro, or nitrous.
Ken
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Hypereutectic
Cast hypereutectic pistons have several benefits in OEM applications as well as some performance applications. Most OEM modular engines with the exception of the extremely high performance
models have been using cast hypereutectic pistons since day one, including the current Coyote 5.0. According to McFarland hypereutectic alloys are highly resistant to expansion, and wear extremely well. This allows OEM manufacturers, or builders in the aftermarket to construct an engine with extremely tight piston to cylinder wall clearances since the piston will not expand enough to cause a problem. These alloys also have a high resistance to scuffing which improves their wear resistance. The biggest downfall to a hypereutectic alloy is its high silicon content. The high silicon content makes the piston more brittle, and under violent detonation, such as that which can occur when things go wrong in a nitrous or forced induction engine, these pistons can be catastrophically damaged.
Eutectic 4032
With new piston designs creating a physical model for test fitting and final design verification is a key part of the final design process.
Eutectic alloys should not be confused with hypereutectic alloys. 4032 is the most common eutectic alloy used in pistons. It does contain some silicon content, however it is much lower and more tightly controlled than in a hypereutectic piston. 4032 pistons are also forged, rather than cast, further eliminating the larger pockets of silicon found in many hypereutectic pistons.
According to McFarland these alloys don’t typically need hard anodizing for the ring areas or the rest of the piston, as they’re strong enough to resist micro-welding in many cases. They posses good wear characteristics, and McFarland says their combination of strength and wear resistance make them well suited for a variety of applications where a forged piston is necessary.
Many high performance engines run pistons with this alloy including endurance racers, forced induction applications, and even some OEM applications. “This is an ideal choice for modern engines with tight controls on the fuel system and ignition timing, where detonation is not an issue,” says McFarland.
2618 X-Material
2618 is the racer’s alloy, also known as X-material. This alloy contains no more than .25 percent silicon. It is strong, yet under heat and pressure it becomes malleable. According to McFarland that malleable characteristic actually allows the piston to distort under extreme conditions without fracturing, or failing. This can save other engine components during extreme detonation.
There are drawbacks to using 2618 pistons though. According to McFarland that distortion which saves the engine, may require the pistons to be replaced as part of periodic maintenance. We’re not talking about after every race, but where racers running a milder setup with 4032 alloy pistons might perform a ring and seal replacement between seasons, a racer with a 2618 alloy piston may need to replace their entire set of rings and pistons.
