If you had a d15 with some bad rings how much would it normally run to bore out the cylinders to fit some new low compression pistons. What else would you have to do to the block to make it turbo friendly? I heard someone say that 10lbs of boost on a d series is safe but how much extra horses can you get from 15lbs on a d series motor? Isnt turbos kits for SOHC cheap? Thinking about building a cheap SOHC turbo motor as a back-up.