Piston rings developments.
Piston rings half more than halved in thickness since the 1980’s.
The initial piston ring configuration as used in formula one was identical to that used in mass production vehicles up to 1989 NA 3.5-litre engine formula, an engine formula where V12, FALT-12, V10, V8 engines reaching an RPM of 13000-14000 was raced. With the difference of using only two rings instead of three. The rings were formed from top ring with a rectangular cross section and an oil ring with a spacer expander inserted between rails.
By 1995 NA 3.0-litre V10 engine formula, such engines that by the year 2000 were reaching the 18000RPM mark, of which was made possible by the development and use of an expanded piston rings of 0.9mm width and 1.4mm tick with a rear expander (behind the ring). In this twin-ring configuration the ring were both the same and identical. The use of these rings increased engine speed by more than 1000RPM before ring flutter sets in. and achieved an oil consumption efficiency of 100KM/L range.
By 2006, the steel expanded rings were replaced by titanium in order to increase fluttering toughness by achieving further weight saving. Because titanium aggressivity would damage the piston grove sides and the expander, a tungsten carbide coating (WCC) was applied to the rings and a DLC coating was applied to the expander. The effect of the reduction in weight achieved through the use of titanium was tremendous. Preventing the increase in pressure in the sump due to fluttering at all engine speeds. And helping to enable oil consumption to reach 150 KM/L.
One important function of the piston rings is to enable heat to escape from the piston to the cylinder. In formula one engines, by contrast, the pistons are cooled by powerful oil jests. In addition, the heat transferring surface area of the expanded rings was also extremely small. The contribution of the piston rings to cooling was therefore minimal, and no issue resulted as by the use of titanium, a material with a low rate of thermal conductivity.
Maintaining the benefits provided by the expanded rings necessitated strict control of the 'taper angle' to very fine limits. (the taper angle of the face of the ring in contact with cylinder wall). This taper compensates and presents a flat contact face to the cylinder when the ring tilts-up when the piston is on its way down.
These rings developments, down to a reputed 0.7mm thick enabled the NA 2.4-litre V8'S to reach 19600-20000 RPM with acceptable ring flutter, blow-dawn gasses and oil consumption.