First, try [normal] xx roll, jump kick telekick air sai, run cancel B2 high pounce. This is the hardest but most damaging combo of ravenous
Using roll, B34 air sai, B22 high pounce results in the same damage as piercing....I think
In the corner try this combo: F343 telekick, delayed air sai, S2, S4 roll, run out, D2, 123 low pounce. 46% meterless
The 1 bar corner version is very different from piercing: F343 telekick, delayed air sai, S2, U3 MB, S4 roll, run out, D2, B22 low pounce. 52% if i remember corrently
Combo with ex roll will look like this: [normal] xx ex roll, run cancel B34 air sai, run cancel B2 high pounce. It's not that hard to pull this off consistently, but if you want to increase the damage by 1% and reduce your succes chance by 90% do B22 high pounce as ender. Note: B22 in that combo only works on medium size characters (subzero, Johnny...), doesn't work on Goro and F/T (the ones I gave up trying B22)