It has a arrow 4 into one race header and a SP engineering muffler. Now the guy I bought it from didn't do the work, the previous owner did. He did not know if it was tuned or flashed or not. I think it runs a tad lean but it does not throw any codes or lights with the exahst valve and O2 sensor removed. So that tells me they had to have done something I just don't know what. What are you thoughts on that?