My car got a little quieter after the headers were installed. (Well the y-pipe, I put the headers on myself). It louder at WOT but at light cruise and just around town driving is mellower, quieter. I had my pipe made by Meineke and I think they used slightly smaller pipe then the stock pipe that was on there. It should still be louder though shoudlnt it ? This is on a 92 L98 with two cars and a exhaust cut-out installed right before the rear-axle.

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92 Z28 L98 350
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Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)