Small update on this. First I've tried like @
eddieflyinv suggested, mostly to find the sweet spot:
+10 @ 2500
+5 @ 3500
+2.5 @ 4500
0 @ 5500
This produces some nice burbles, but also still some harder pops if you really want to. Sweet spot seemed to be around 3-3.5k rpm, so around +6 I assumed, so:
Then I tried +6 constant, which was to loud in the low revs
Also tried +10 constant, which was very nice in the low revs, but didnt produce any sounds above 5k rpm, so it seems the sound differs with RPM also, even if keeping the timing constant. For now I'll settle with the +10 +5 +2.5 0 settings posted above, might try something like +10 +5 +5 +5 or so in the future, but don't think it will make that much of a difference.