On the turbo exhaust manifold, there is a very large area to the left of the collector towards the number #1, #2, #3, #4 cylinders that hangs really low into the path of flowing air. It takes some work, but if you have so long burrs or long stones, you can get in there and really open things up. There is a lot of room for gain here, but takes patience when grinding as it will take awhile to remove the material. Cylinders 1-4 currently only have a small opening to travel through to make it to the collector. Open this up, and you can help flow in the manifold dramaticallyas this is a pretty good sized bottle-neck