I changed mine at 1600 and again at 7500, and then at 7500 intervals from then on. The oil I use is Mobil 1 5W30 EP. I trust my brother on this subject, so I'm using this oil based on his advice. We did an oil analysis a few changes ago and it seemed to confirm this is the oil to use for this engine, and it is good for right around 7500 miles. He posted the oil analysis on another forum:
http://www.bobistheoilguy.com/forums...Number=1851142