You might be right about belt durability. I have a R-40 that I put my Modified RB .21 in and the belt has held up I ran it several times before I put it up and started playing with my 1/5 scale MCD. The motor was modded by RB but it is not one of his Extreme mods like you get
With my V1rrr I am going to have to do some cutting to put a .21 in that is why I was looking at the OS .19 should drop in without any cutting. It is suppose to be putting out double the power of a stock .18 TZ OS claims 2.3 hp compared to 1.6-1.8 hp for the .18 TZ.