It's the exhaust system air intake and a bit of programming that makes
the difference in available horsepower.

I have one of the 2003 3.5L Nissan Altimas which was an awesome car to
begin with, but now I've done some performance tweaking with the
engine, exhaust etc .. and now the car screams.  I've taken it to the
dragstrip a few times and I'm running better times than most of the
naturally aspirated cars out there... including all of the old muscle
cars.   If your interested in some performance parts for your altima
check out www.seffects.com/altima.asp.