Dropping your freshly rebuilt Pull-A-Part sourced race motor into your Lemons car and having it run smooth at the first turn of the key.  That is what's awesome.  Pulled the head and oil pan and looked it all over while replacing all the seals and gaskets as well as water pump and thermostat. First time I've ever taken an engine that far apart and put it back together.  Time for a celebratory adult beverage.