Apaches have bigger valves, 2.14I vs 2.055I, bigger chamber and the valves are Hollow stem (lighter). That is good stuff, but in the grand scheme of things until guys start to run cams in the .700+ realm the Eagles,6.1's and Apaches will all perform pretty equal with work done to them IMO. If building a big inch, 400+" engine, I would vote Apaches with a .600+ lift cam and some porting work. If building a big boost or nitrous engine with same size cam I would go with 6.1's or Thiteks because of valve selection and chambers would allow more piston thickness vs. compression.