Hard to say, spyghost. You're not giving much here in what you're looking for.
If it's ring de-coking, you should be in pretty good shape in the 1st cleaning phase. Some severe conditions will see continued benefit during the rinse phase and may indeed take a 2nd treatment to be fully restored (or as good as they're gonna get). That's a diminishing ROI ..but it was what was required.
It would be hard to measure that over something with tar like hard deposits ..there you're really in for a long haul.
Now if you're trying to achieve your "new engine look", then ...hmmm..I dunno. Some of the stained surfaces may not see a constant oil bath ..and may take time to be cleaned ..and even then, it may depend on the porosity of the metal on whether you can get it prestine.
