Coilovers really do compliment an already well balanced car with excellent cornering ability.
And dont worry about harnesses and race seats... you wont need those until you go with wide, sticky tires.
I need them now, I am falling out of my seat coming out of 13 at Carolina Motorsports Park and would definitely benefit from sticking in place better everywhere else.
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2002 Boxster 2.7
2008 Navigator L