Buick's flagship series consists of two sedans that vary primarily in power points and on-board amenities. Park Avenue Ultra ripples with energy due to a mechanical supercharger used to extract more-than-normal power from a six-pack engine. Without the supercharger, Buick's 3.8-liter V6 for base Park Avenue musters 205 hp. Apply the supercharger and output climbs to 240 hp. New fender portholes on flanks mark the 2003 Park Avenue Ultra, which also carries chrome-plated exhaust tips. Wood-grain trim like burled walnut in the cabin streaks across door panels, steering wheel and instrument panel, with new aluminum sill plates fixed to front door ports. Turn signal chevrons show up in external rearview mirrors.