high-pressure gas shock. German manufacturer august Bilstein licensed the design and perfected it. During the process they learned that a key element is the piston seal; pressurized gas or not, if the seal failed to reliably separate oil from gas, aeration would still occur. Bilstein devoted considerable resources to developing a rugged, self-lubricating and long-wearing seal that optimized their monotube high-pressure gas design.
   When it appeared in 1983, the new C4 became the first U.S. vehicle to offer Bilsteins as original equipment. In 1989 Bilstein also supplied the optional FX3 electrically adjustable shocks. Since then some 30 other GM vehicles have also worn Bilsteins ranging from the Z71 pickup to the police-pursuit 2WD Tahoe. In recent years the German manufacturer's OEM U.S. business has blossomed to the point where an Ohio manufacturing plant was constructed to handle the demand. Bilstein continues to concentrate on high-pressure gas mono-tube models for both street use and racing with several available for Corvettes from model years 1963 and up.
   The mono-tube design has other advantages. For example, given tubing of equal bore diameter,