MacDonald Motorsports uses SCT 4 bank chips ( #6600) exclusively for its Custom Chip Tuning. The chip holds 3 custom tunes, plus the original tune. It also has a “no start” position which disables the car for added security when left unattended. All tunes can be accessed in real time through the use of the micro switch and cable included in with the chip. While being the older method of installing the tune, it has one big advantage. You can switch tunes on the “fly” This is particularly important to people running Nitrous Oxide, and different types of tunes. (Power, Economy, Towing, Valet, Speed Limiters etc.)