The GT-40 intake was a great intake back in the day. It was cool looking and flowed well compared to many of the aftermarket heads available at the time. Unfortunately, that was more than 15 years ago. A stock GT-40 intake flows about 230cfm stock. The upper intake uses thin walled aluminum tubes, so they can be ported. The lower intake is cast and can be ported. Some companies are getting as much as 70-80cfm extra by porting the lower intake, straightening the runners and re-machining the flanges. There is a lot of cutting and welding to make this work and will cost about $700 for just the labor. You will still be limited by the upper intake, however. I would not recommend the GT-40 for more than 450 hp on a naturally aspirated motor and not more than maybe around 500-550 on a blower or turbo motor. There are a bunch of intakes that are way better and cost less money, such as ones from TFS.