I think you will find all the VCT engined cars have a duel system from about the middle of the car back. If you have a look above the tip there might be a second pipe that has its end capped. The tip is an aftermarket item (or bought OEM then put on after purchase) cause the AU's all have the little oval tip no matter what engine is in it (ie V8 or VCT).
Hope this helps.
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AUII XR8 (200kw), Silhouette, Body Kit, Hawk Wing, 5 Speed man, Premium Brakes, Premium Sound, Genie Extractors, 3" exhaust with twin 3" tips, K & N filter with air scoop, Polished Inlet manifold, MAF & 70mm T/B, T series interior handles & Gear stick ring, Chequer plate, Momo Pedals.