on your b13, it is the outter belt. it does boost performance and gas milage. i did it. its easiest if you take your passenger wheel off, and then take off the plastic sheilding. loosen the a/c belt tensioner...the bottom most pulley attatched to a bracket and nothing else...and then the belt will come right off. if you don't think you'll loose the belt tensioner....i lost mine, thats why i saying this....take it off or tighten it very tight. if you don't, it will rattle and bug the hell outta you, at least it did me. if you have any questions, you can pm or email me, no prob. good luck.