Hey welcome to the forums and the hobby, once you start, your new life begins haha. Im not exactly sure on the 18, but for the sh 28 at least, i stay at about 240-250 to be safe. And dont ever go over 270. Dont tune for temp, make sure it sounds good, and runs good, and if its running great, but its temps are 270, richen it a little bit to be safe. Just make it run its best, while staying at a good temp.