hi there, i have 2 engines i really like at the moment, The Rex P5 and the CMB EVO2 R Raptor.. The Rex has insane bottom end and reliability and the CMB has more top end than i know what to do with.. The P5 has lasted me 12 litres so far and i still cant turn it over by hand. The longevity of most engines come down to 2 or 3 things IMO. Quality, Cooling and Fuel. Quality to begin with, Good Cooling will ensure engine life and good fuel will keep an engine happy.. Engine life will be enhanced by tuning to your conditions... if you tune for short tracks you can afford to tune a little leaner on the top as opposed to long tracks where you would rev high and run sa little richer ...