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Much of your time is going to depend on your suspension and what traction you can achieve in addition to your gearing and horsepower. 16s would be my guess. Slower if you blow the tires up when you launch. I see some nice late model mustangs running low 14s upper 13s. 350-400hp in a classic Mustang with some suspension mods and good tires should get you in the 13s possibly in the 12s.