Hello everyone, I am very excited to have found this forum. i have been reading a lot the last couple of days and now am more confused then when i started. I am right now in the process of building a high performance 12 valve 5.9 cummins. it is my daily hotrod and will be driven everyday. Right now it is at the machine shop being balanced bored, shot peened rods, getting a girdle, main studs, head studs, new pistons flycut with ceramic coating at 16.1 compresion, new cam and lifters. will be at around 700 hp for everyday driving with a future goal of 1000+. Doing all of this is not terribly inexpensive. So in an attempt to protect this investment i have been reading here. I am going to get an amsoil bypass filter system hoping that the filter will help the inevitable high soot levels with my large amount of fueling. My machinest says i need to run a high zink content oil for the first 1000 miles to break in the valve train. after that normal oil. so my question is when if ever to switch to a synthetic oil. I was convinced that synthetic was the way to go but after being around here it seems that conclusion is debateable. but i havent seen it discussed for a high horspwer diesel. I like the idea of a 5-40 oil for the many cold starts it will endure. with temps down to -10 during winter months. so if this were your engine what kind of breakin oil would you use after the first 1000 miles, dino or synthetic. and what type/brand of oil would you use hoping for longer OCI, hoping to change oil 1-2 times a year, around 20k miles driven a year. thanks.