Steeda's Patented Timing Adjuster lets you advance or retard your ignition timing up to 10°, so you can tune your car for optimum performance. Advancing your ignition timing can net up to ten horsepower and better gas mileage. Supercharged Mustangs can also benefit by setting the timing back a few degrees, which allows you to run more boost and avoid detonation. We went the extra mile designing this part, to make sure it will fit with Steeda underdrive pulleys or Vortech and Paxton superchargers. Will not work with "piggyback" style underdrive pulleys. NOTE: May cause the check engine light to illuminate if the timing is advanced to more than 14° on 1999 and newer Mustangs Application: 1996-2004 Mustang GT 1996-2001 Cobra