Bob posted: "...Maybe I'm missing something here, but it seems to me that if a boat with turbo gets 8 knots at 1800 RPM, removing the turbo will result in the same speed at 1800 RPM. .. You are right on....Thats true. But the listee listee wants to do something different. Basically he wants a smaller HP engine. At any given speed, say eight knots, it will still take the same HP to achieve that speed after the change as it did before....unless propeller efficiency or engine efficiency is a bit different....(Otherwise we'd all go faster with smaller engines.) The listee wants to cruise at trawler speeds. He is properly concerned about running higher HP turbos at low RPM because of engine turbo fouling. So his thought is to remove turbos, put in smaller injectors and make other changes necessary to de rate his engine to a lower HP. He may also need to reduce his prop size.... Then he can run his engines at a moderate RPM, develop less HP, cruise slower, and ... ta, dah!!!!.. achieve fuel savings....on the order of 20% according to my prior estimate....Or to say in another way, he'll be cruising slower and burning less fuel because he'll be generating less HP....but keeping his engine clean running. As an aside, this has been a popular modification on 58 ft Hatteras Yachtfish many of which were powered with DD 8V71T's...I believe the 58 will cruise about 8 or 9 kts at 1200 RPM with naturals....but this would be a rather slow RPM to run turbo equipped engines....they may be likely to get fouled turbos at this speed. But it's possible that a RACOR CCV (which filters oil mist from combustion air going to the turbo and returns the oil to the crankcase) (similar to Walker Airsep) MIGHT significantly reduce this concern...I don't know for sure....(I had not thought of this in my earlier posts.) I'm neither endorsing nor criticizing this proposal just addressing the question asked... Cheers, Rob Brueckner 1972 Hatteras Yachtfish