The AG-330 Start Cart orginally were Buick wildcat 401 cubic inch V-8 engines developing 400 horsepower. There were two Buick engines mounted tandem side by side with automatic transmissions. They were coupled together with a steel woven drive belt to drive a vertical shaft that was inserted into the starter mechanism on the bottom of the SR-71's engine.

By the end of 1962, only two A-12s were engaged in flight tests. Full test speeds could not be reached since the J-58 engines were not fully available and were experiencing problems.