Every Cobra in stock form is way off the charts on A/F. That was part of the stock program. Anytime you run a smaller pulley, I would always recommend using a chip. Some people say you don't need one on a pulley the size of a 3.1 or larger, however you will always benefit with a chip tune to find added HP and straighten out the A/F. If you are going with a 2.80 pulley, I would recommend getting one from Amazon. He has burned enough with a 2.80 pulley, that he was right on with mine on the first burn. Not to mention he has great customer service, and that is always tough to come by these days.JClifton said:I'm off the chart rich from ~4800 on up would I be ok with going to a 2.80 upper, then in a month or so getting a diablo?