I wasn't sure if everyone knows this yet or not however,there's now headers,and quite a few exhaust systems availible for the PT Cruiser. Thermal Research&development makes a dual exhaust for the PT. Borla makes 3 different exhausts, single pipe,single outlet,single pipe dual outlet,and dual pipe dual outlet. Plus there so far is 2 companies that make headers: Borla,and JBA headers.
Go to
www.borla.com Also
www.jbaheaders.com
There's also af ew other places you can get go fast goodies for PT's. Howell Automotive,they have large bore 55mm throttle body's,underdrive crank pulley's,limited slip differential,suspension upgrades,etc.
www.howellautomotive.com Antother good one is
www.ptcruiserparts.com One thing they make is a cold air intake,there are many others though.
Crane cams makes performance camshafts for the PT Cruiser
www.cranecams.com
2 companies make turbocharger kits for the PT: Hahn Racecraft makes a turbo kit that will give a 60hp boost.
www.turbosystem.com I think Stebani is the other company,one company even makes a supercharger...not sure which one though,might be Whipple.