so does that mean it essentially works exactly like MASC? need a 3, then 5, then 7, etc... to keep using?
On 'Mechs, pretty much. The two key differences are that when when you fail (a) unlike MASC, the supercharger is automatically destroyed and (b) instead of risking leg damage when that happens you roll to determine crits once and apply any that result directly to the engine.
Also, unlike MASC, you can install superchargers on vehicles, but the rule regarding what happens on a failure
there is poorly written to the point of making basically no sense whatsoever. On the one hand, you're supposed to roll on the "appropriate Determining Critical Hits Table" -- which vehicles don't actually
use since if you get a potential critical hit on a vee you simply skip ahead to rolling straight on the relevant critical hit table once --, and then you're supposed to apply any results to the motive system, which has nothing to do with regular critical hits
at all.
(I suppose the idea
may have been that you're supposed to roll for up to three possible critical hits as you would for a 'Mech and then apply any results on the Motive System damage table going down, with anything beyond "immobilized" killing the engine as well...but that's only my best hazy guess.)
Edit: Actually, according to
this thread it seems I may not have been too far off the mark. The book itself still obfuscates things far too much for comfort, though.