Honestly, not many, if anywhere. That car is basically a dinosaur considering the SR20 wasn't introduced in the Sentra until late 1990.
The best thing you could do is be creative and fabricate your own parts. Custom exhaust can be done easily, you could also fabricate your own intake.
Check
www.sentra.net for more information.
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-Nuke the bastards-
Stormy
'98 SE(R) w/ HS CAI, HS G3 Header, Custom 2.25" Exhaust, JWT S4 Cams, UR Pulleys, KYB AGX's, Eibach Spings, Courtesy F&R STB's, ES Mounts, ES control arm bushings & shifter bushing (NI), Brembo X-Drilled Rotors w/ Axxis MM Pads, 205/50 Pirelli P700z's
www.WhiteLineRacing.com