Hello, thank you all for the helpful advise in the thousands of posts.
I have an '85 300D in immaculate condition with 132k on it. I was fortunate enough to purchase it for only 3,200 bucks in NC about three weeks ago, and i just finished installing an entirely new a/c system on it. I am pleased with it after having done all the requisite MX any newly bought car should get, but have a question regarding converting the existing restrictive exhaust with the trap oxidizer and turbo to be swapped out from a 1979 617 motor 300SD version of the exhaust manifold and turbo. I have heard this motor run in the rear-ended car and it has 212k on it. My primary concern was improving the fuel mileage to better than the 22 on the highway that it is getting now. 22 is the best the 85 300d california car will do according to many sources since it has the excessive emmission controls on it. I have heard that the 300 sd 1979 model gets about 28 or so, whish would make it worth the 500 bucks for the complete motor with all the trimmings. What else should be converted in addition to the exhaust manifold and trap? Thank you all for the excellent, professional advise. Adam Bush