All the features of the famous Dyna "S", plus the special feature of firing the front and rear cylinders independent of each other, allowing a much more accurate timing of each cylinder. Dyno and top-speed testing have shown a dramatic improvement in power in all areas; bikes with hotter cams show the greatest improvement. Made in the U.S.A. NOTES: Not recommended for use with OEM coils. An advance weight mechanism is required. This unit must be used with special Dyna coils. Tach adapter is required when using an electric tach.