very unlikely that you will notice a difference in MPG, and I doubt the HP gain from it will be seat of the pants significant. MPG may probably be worse in the beginning since its hard to keep your foot out of it when you get a new exhaust. Probably plateau and be the same or slightly a tenth better.
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2001 Trans Am WS6 •SLP Loudmouth II •UMI Suspension •12.857 @ 109.57
1996 Trans Am WS6 •Pacesetter Longtubes •Strange 12 Bolt •Spohn Suspension •11.152 @ 123.85
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