I just dropped my 1980 SD33t at the muffler shop to finish this modification. I bought the 2.25 downpipe and installed it and also changed the air cleaner. I am trying to get the engine to breathe easier. Right away I heard something new. The turbo actually makes a noise! I hear the whistling that you hear on all newer diesel trucks. I think it is running better. I will tell you more when it returns from the muffler shop. Pretty exciting for me. I hope we have the RMIHR this year so I can show off my work this summer in Kremling or Salida CO. Keep Binding !