Engineering 'Scaling', in its proper context is only just above business studies, and similar to maths, so its not great. When we are talking about how well raw marks translate into aligned exam marks, i've heard engineering is comparable to 3u maths (E4 cutoff is ~68%), although since engg is not very popular, there's no stats or data I would personally rely on. It is important not to get these mixed up, especially since engineering has poor scaling, but it also has low raw mark cutoffs.
for raw marks i'd say 75% will get you a 90, but there's no guarantee that 90 in engineering is counted in ur top 10 units i.e. according to atar calculators, an 88 in physics gets you a scaled mark of 41/50, whereas a 90 in engineering gets you a scaled mark of 38/50, so even tho u got B6 in engineering (and B5 in physics), its scaled mark is not as good as physics, or lots of other subjects for that matter.
I hope this answers ur question.