Originally Posted by VikHatBer
What has to be done to cruise a pair of 1271's at 1000 RPM's without harming the engines over the long run? I heard that the turbos have to be modified to prevent carbonm buildup that results from low RPM cruising. Any help would be appreciated.
I run a set of 12v71TI's like that, BUT I run them at 2000-2050rpm's for 30 minutes every six hours to clean everything out (per a Detroit Diesel factory recomendation) turbo's and airboxes. These particular 12v71's are low hours smoh, but tend to run a little on the rich side at 1,000 rpm's or less and sometimes I would get some turbo caking and hear a whine coming from the turbo's. Running them at cruise would clean them out. Also I use a product called "Diesel Kleen" it does a terrific job at eating algae in diesel fuel, and has a little more cetane and stuff and they tend to run better and cleaner with it. These were covingtons, it depends who marinized them as Johnson and Towers tended to be the most "hot rodded" of the detroits and had larger injectors, turbo's etc then the Stewart and Stevens, Covingtons, and I forgot the name of the other company that marinized a lot of them. I see a burn rate of 10-12gph (both engines) at 1,000 rpm's and 90-100gph at 1950rpms. This particular yacht run's 16.5-17knots at 1950rpms and 9.5 knots at 1,000 rpms so it really doesn't pay to run it at cruise.
However if you want to run at 1,000 almost all of the time. Another yacht I ran was setup to run like that with 8v71TI's, at rebuild Detroit Diesel went to one size smaller injector....... instead of the 110's(lph) they installed 90's(lph) and adjusted the rack accordingly. You'll have to cut a few inches of pitch out of the propellors if you do this and it will effect cruising speed by 5-20%. However, that yacht ran crystal clean at cruise and slow speeds and all of the way around even if you ran at 700rpm's all day. Also fuel consumption at cruise went from 45-50gph (both engines) to 30gph (both engines) at 1950rpm's and cruise speed went from 15.5 knots to 13.5knots at 1950rpm's. This was actually the best running set of detroits (aside from DDEC's) I've ever ran they'd start up and idle perfectly with no visible smoke whatsoever, they ran smooth and felt torquey down low. This was a 58' Hatteras YF