The hfc's add a deeper sound and some torque. With a full exhaust i noticed it on my car with the butt dyno, but that could be in my head. I would search the site though someone is selling some nismo's i believe for less then 300 shipped. Just jack the car up on stands or ramps. Its less than three bolts in four places. Takes about 20 minutes. You will have that self satisfaction everytime you turn the key knowing you did it. With the money saved you can buy a ztube or intake spacer to help on the intake end.