Abradable powder coating is a new, low cost, high volume process for piston skirts. It brings substantial benefits to the power cylinder by 1) reducing cleaances and 2) improving the oil film for lower friction. 1% to 2.4% horsepower increases are documented in 'apples to apples' testing using abradable powder coatings on piston skirts in 2strokes and 4strokes respectively. We believe this translates into fuel economy, but have not directly measured it to date. Measurable durability gains are well documented, and peak power lasts longer. google 'Jason Farrell Case Study' for dyno data and parts photos.
The gains come because the APC coated pistons are installed snug (too tight). Upon start-up, APC texture quickly wears in to match the bores. Each piston is uniquely honed in to fit its bore while the engine is assembled, is hot, and is under load. The fine tuned fit is a permanent geometric change to each skirt, because once there is room for the perfect oil film, the wear STOPS. Abradable Powder Coating coating actually locks in the ideal barrel shape for EACH bore. Engine builders normally observe 40-50% reduction in cold clearance at gage point AFTER extended use at peak power...with NO SCUFFING.
The improved geometry of each piston reduces clearances and friction -simulaneously. The pistons rock less, less oil squishes(free energy), dynamic ring sealing improves, ring motion and wear is reduced, slap and associated collateral damage is reduced, along with noise. There are design opportunities such as lower tenion rings, smaller crevice volume, stiffer skirts, etc.
The friction of the piston skirt is reduced because of the larger load bearing footprint of an APC coated skirt. The coating assures the minimum oil film thickness across the entire skirt, which corresponds with the lowest friction area on the Stribeck oil film model. The 'leakdown length' of the oil film is lengthened, so the oil film cannot collapse. No boundary lubrication means no wear. RpK is zero, RvK is big- ideal tribological surface after break-in. Thats why it lasts after break-in. Its All About the Oil Film!
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