The 2003 2.2-liter common-rail turbo diesel for European PT Cruisers.

Engineers at HP Pelzer Automotive Systems, Troy, Mich. (www.hppelzer.com), chose a polypropylene long-fiber-reinforced thermoplastic (LFRT) over fiber-reinforced sheet-molding compound (SMC) for the belly pans of diesel-engine-equipped PT Cruisers. The material, Compel LFRT, is produced by Ticona, a business of Celanese AG, Summit, N.J. and Frankfurt, Germany (www.ticona.com).

The belly pan sits underneath the engine and helps silence road noise to meet European regulations. Its 3-mm-thick base is about 3-ft square and extends from the radiator to the firewall. "The part needs to be flexible and must withstand impact from stones and other objects," says Pat Wundrach, program manager at HP Pelzer. "We first compression-molded the belly pan out of SMC, but road tests showed it was too brittle. We turned to an impact-modified grade of Compel LFRT reinforced with 1-in.-long-glass fibers in a polypropylene matrix."

Compel parts have a notched Izod impact strength of 21 to 29 kJ/M2 at temperatures from -30 to 100°C, and good resistance to gasoline, motor oil, antifreeze, and other automotive fluids. The thermoplastic flows well to provide consistent glass-fiber concentrations and smooth surfaces. In processing, the Compel LFRT parts are usually plasticized and extruded into a compression mold. This contrasts with SMC, where the typical process is to heat a mold and compress a cold blanket.