First difference: a passing motion received, or a vital act of the will
Thesis LXXIV. On the nature of efficacious grace, however, they differ in many respects, as Jansenius notes and reports at length in De gratia Christi Salvatoris, book 8, chapter 1. For the recent Thomists, the grace that physically predetermines the will is, as explained above, a 'virtual motion' with a kind of incomplete being, present in the will in the way colours are present in the air and impetus in a thing that has been pushed.
For Jansenius, that grace is a real and true affection of the will, consisting in a love and desire for heavenly and spiritual good, by which the human mind is carried upward sweetly and with immense joy. So for the Thomists this efficacious aid is only received passively in the will, while for Jansenius it is something that proceeds actively from the will and is a vital movement of it.
Latin
LXXIV. Caeterum circa naturam gratiae efficacis in multis dissentiunt: ut prolixe notat & refert Jansenius de gratia Christi salvatoris libro octavo capite primo. Nam Thomistis recentioribus gratia voluntatem physice praedeterminans, ut supra fuit expositum, est motio quaedam virtuosa, quae habet esse quoddam incompletum; & in voluntate est per modum quo colores sunt in aere, & impetus in re quae impellitur. Jansenio vero gratia illa est affectio realis & vera voluntatis, consistens in amore & desiderio quodam boni coelestis & spiritualis, quo suaviter & cum ingenti jucunditate sursum rapitur animus humanus. Ac proinde Thomistis efficax istud auxilium in voluntate tantum passive recipitur, Jansenio vero est quid active ab ea procedens, & motus illius vitalis.