Honda S2000 Mugen

The standard Honda S2000s have been powered by the 2.2-liter F22C engine. Mugen engineers didn't tamper too much with the 242bhp engine itself. They just tuned it slightly and bolted on a new exhaust manifold that's about nine pounds lighter, with much less flow restriction. The new design is claimed to result in a boost of around 5-horsepower. 

Coupled to this is a new sports exhaust that gives a mean-yet-melodic growl, especially under load.
What you get is a well-balanced, subtly aggressive sports car that's rewarding to drive and will keep pace with rides costing thousands more.