Looking to start my turbo build

it is quite expensive but the drive ability and tuning become much greater. i know its going to create some extra weight and take up space. but..... i hope that it'll grab some attention and be fun to drive. i was just checking on crower cams. They offer custom cams for the /6 also. i haven't had a chance to contact them yet though. but i did have a question. i was looking at some of the turbo slant builds. the higher boost cars are using o-ring gaskets on the cylinder. what is the threshold that people start doing this?