The only reason I can think of why there's different filters for evo style motors and the twin cams is, different micron ratings they're supposed to have. Evo's were said to need a 35 micron rating per Harley. And twin cams were 5 or 10 micron. I'm guessing that's because twin cams have plastic cam shoe tensioners that shed small plastic chips during operation. And some need to be replaced by 20k miles on earlier models. Those chips can plug oil passageways, and piston oilers. When the twin cams came out, they also rerouted the way the oil flows thru the motor. On Evos oil came from the oil tank and went thru the motor, THEN was filtered before returning to the tank. On twin cams, the oil is filtered before it enters the motor. This way no plastic chips can be pumped into the motor. You can look at different sources and find that the filter numbers don't always jive for the motor in question. I'm sure every combo has been used at some point or another with little to no catastrophic results. Myself, I just buy a filter from Harley because I don't like to wonder if I have the wrong filter on my bike.,,,
