[Spikesoftail]

I'm not an Evo expert by any means, but 15w-40 sound like way to thick to be runnin through a newer motor. Most new engines have much tighter tolerance's and much smaller oil passages than older engines did, thicker oil actualy will damage you engine more than help. Like I said I dont know enough about X's, to be much help here, but from what I have seen this is a huge mistake area for a lot of performance guys. Thinking thicker = better lubrication, doesnt always work out right