The 67 [ 11cc ] is the prefered engine size for 1/8 th scale hydros. you need to find out what engine supplier has what available such as CMB i know are a good strong and reliable r/c engine as opposed to the old K& B 67,s that loved to break conrods unless you fitted a better rpm brand rod. so who stocks OPS / O.S. / CMB / PICCO etc, thats what you need to find out especially for spare parts when needed.