Forged Steel, monotherm pistons for the 7.3L Power Stroke
Since we are near the end of the HPCR injection system for the 7.3L Power Stroke…we are taking a proactive approach by developing stronger pistons for the engines that will be subjected to very large amounts of fuel.
Mahle Motorsports divisions has released steel monotherm pistons for both the Duramax & Cummins engine, but have no plans to R&D this type of piston for the 7.3L engine.
The raw steel forging starts out weighing 12.5lbs…per piston…(not including the piston pin or rings). Finished weight (post machining) should come in @ 3.3lbs.
For comparison, an aluminum piston for these engines typically weighs around 2.07lbs…
Adding weight to a piston is not something that is recommended for a street vehicle, and high rpm (competition use) engines will need to have other modifications to reliably run a heavier piston; including balanced rotating assembly, high strength aftermarket connecting rods, & blueprinted (bearing) oil clearances.
While there are downsides to the heavier piston, the material benefits of steel make this a necessary progression for heavily fueled, competition use engines. Very high powered engines produce very high exhaust gas temperatures, which can cause the aluminum style pistons to fail. Aluminum pistons typically fail due to either fracturing (due to stresses caused by multiple heat cycles or by very high cylinder pressure), or they can ‘melt’ from excessive injection pressure and heat caused by the very high injection pressure & rate of a competition injection system.
Steel also has a linear expansion coefficient about half that of aluminum; which makes the steel piston much less likely to ‘grow’ under very high temperatures, and cause significant engine/cylinder wall damage. An aluminum piston would have to have significantly looser piston to bore clearance than a steel piston.
By being able to run a significantly tighter piston to bore clearance, with the steel piston, much more energy will be transferred from the combustion event to the connecting rod, resulting in more power delivered to the crankshaft.
Here is a picture of the OEM style aluminum piston compared to the raw steel forging.
Here is one of the final design schematics for the Swamp’s Diesel steel pistons.
