The black violin case that conects the MAF to the T/B. I found the mod on RichardM web page. It dosen't help as much as a larger MAF or the 3 inch tube. I noticed a change in power. About the same as when I got a K&N. But the big thing was gas milage. It was up 3 MPG. I recomend any one doing this if you don't have the funds for a RM tube.