The HPI method to break in is utter garbage. That is 1/2 the reason your engines toasted when they did. The fuel may be partly to blame.

Traxxas Top fuel is a castor/synthetic blend, supposedly an 80/20 blend with the 80 being synthetic. In fact most commercially made fuels are an 80/20 blend more often than not.

I break in car engines on 18% oil airplane fuel most of the time. They handle the extra oil just fine, they just make more of a mess and tend to rev a little slower albeit near the same top revs as normal fuel. I only use castor oil in ALL of my fuel blends. I like to know what's in my fuel and more importantly I want to run the fuels the engines were designed for. Run a lapped iron piston/steel sleeve engine on synthetic oil based fuel and miss your piston seal goodbye. It would still run but some engines NEED the castor varnish buildup to keep the piston seal at or above par.