I'm really amazed by the worksmanship by some of the people on this site, so I want to be clear I'm doing amateur work with poor tools. That said, I modified my stock exhaust manifold, as others have done, and perhaps went slightly farther than most. I had worries about structural integrity, and still do, but haven't seen any posting about bad outcomes with this mod, just dire predictions. Here's my experience, FWIW:
I took my stock manifold and ground the stud supports down all the way flat, so the stud holes were open all the way through. I also opened the channels a bit more and shaped the center divider. I was experimenting with tools for the job, but just working in a home workshop, and it was a PITA. I ended up using many different tools for different parts of the job, but the key was a custom flexible extension for an electric drill that held a grinding ball that I pushed through the passages. Basically a roto-rooter concept. I thought porting the head was a bit easier than the exhaust mani. It is running well for two months, no cracks so far. I expected it to crack, but figured I was only out my time if it did, and it was a learning experience. So far it hasn't cracked. I like the way it drives, but won't have dyno numbers until spring. It seems pretty good for a stock turbo w/12 psi, compared to my last car that was all stock at 14 psi. I wonder whether the longer tubular manifolds have any disadvantages to the stock manifold. The stock one seems very overbilt compared to aftermarket ones, so maybe I'll get away with the rather large amount of material removal.
I took my stock manifold and ground the stud supports down all the way flat, so the stud holes were open all the way through. I also opened the channels a bit more and shaped the center divider. I was experimenting with tools for the job, but just working in a home workshop, and it was a PITA. I ended up using many different tools for different parts of the job, but the key was a custom flexible extension for an electric drill that held a grinding ball that I pushed through the passages. Basically a roto-rooter concept. I thought porting the head was a bit easier than the exhaust mani. It is running well for two months, no cracks so far. I expected it to crack, but figured I was only out my time if it did, and it was a learning experience. So far it hasn't cracked. I like the way it drives, but won't have dyno numbers until spring. It seems pretty good for a stock turbo w/12 psi, compared to my last car that was all stock at 14 psi. I wonder whether the longer tubular manifolds have any disadvantages to the stock manifold. The stock one seems very overbilt compared to aftermarket ones, so maybe I'll get away with the rather large amount of material removal.