As Hack said, the Mach 1 s have not been there long. Any track motor is going to need maintenance much quicker then a a street engine. Yes the failure rate for the 15-18 Voodoos' is a bit higher but not aw high as many think. The 19 20s are about the same as the Coyotes at this point. The Voodoo has been around for almost 9 years and the Coyote still hasn't achieved the power level of the VooDooI have found that voodoo owners have very thin skin.
All the track attack GT350's had at least one engine change, many also had trans failures. Ford didn't want to put in the development time to damp the vibrations. Too bad it is a cool engine.
I don't remember hearing any of the Mach 1 track attack cars getting new engines. I know for sure that not all of them have or will.