ACR Joe
Enthusiast
Definitely headers. Lots of choices out there. I chose a complete Belanger system from BTR (Tom Welch). Power gain, quality, fit and finish, installation ease and sound are all outstanding. Do whatever is necessary to ensure that you don't get a check engine light. With just exhaust mods, my otherwise stock ACR ran 12.1's @119 mph w/o slicks at E-town a few weeks ago. That's a 0.5 sec. improvement prior to headers. I doubt any other single, moderate (i.e. not turbo or super charging) parts upgrade could produce such dramatic results.