Here's a time-proven 2.25" exhaust made with mandrel bent aluminized tubing along with stainless steel Borla muffler and 12" Techtonics resonator. Typical gains are 7-8hp. Fits '85-'92 Mk2 Golf with 45mm catalytic converter. Clamps and rubber hangers are included. Two year warranty on tubing and resonator and lifetime warranty on muffler.
For those that require the exhaust a bit quieter consider adding the optional second resonator and/or a venturi.