Coatings
Pistons coatings are applied when the surface of the aluminum can't cope with the environment. JE's thermal barrier crown coating helps to maintain surface hardness and resist surface erosion and pitting due to detonation. This coating may allow a piston to last longer under high temperatures. Although the crown coating is beneficial to the piston, the engine builder should consider the effects the coating may have on the total system. Since less heat is being dissipated through the piston and rings, it is being reflected elsewhere in the combustion chamber. This extra heat may have an effect on other components in the engine. Many builders choose to coat their cylinder head chambers, valve faces, and exhaust ports for this reason. Skirt coatings help reduce cold start scuffing, surface friction, and wear. In some cases a skirt coating can also be used to decrease piston to cylinder wall clearance safely. JE's most popular skirt coating is our proprietary Tuff Skirt. This coating is up to 0.0005 inch thick per surface and is designed to have improved wear resistance when compared to other coatings on the market.--Stephen Goyla
Dishes
When it comes to dished pistons, the terminology can be confusing. While both dish and dome pistons reduce the static compression ratio, there are important difference between the two. "The main difference between the two is their shape, with a dished piston having a simple circular dish and inverted domes having a special shape that matches the cylinder head chamber. Many people refer to inverted domes as D-shaped dishes," explains Golya. "Contrary to some of the information out there, the shape of the dish has very little impact on valve deshrouding and airflow. Heat distribution has more to do with the thickness of the crown underneath the dish than the shape of the dish itself. The design and contour of the underside of the piston play a big role in how the crown distributes heat. Inverted domes are commonly known to provide greater combustion efficiency than full round dishes because they direct the air/fuel mixture into the chamber better, although this effect is greatly minimized with forced induction. Conical and spherical dishes have shown some power gains, but not across the board with every combustion chamber design. Unfortunately, their thin center sections and thick outer sections trap additional weight in the piston crown."