FDL-16D... There is evidence to suggest that the C and D engines are for all practical purposes identical, with the exception of governed engine speeds (the A and C engine both had idle speed set at 400 RPM and full speed at 1000 RPM) with an increase in full speed to 1025 RPM. Idle speed remained the same.
While I'm at it, I should mention that all FDL engines from A through F series had a compression ratio of 12.7:1. We cannot be sure as to when or how camshaft profiles may have changed; this is not referred to generally and you'd need a parts manual to get that detailed information.
Returning to the near identical features, mechanically, of the C and D engines: An interesting blurb in The Railway Gazette, October 1, 1965 (provided us by Steve Palmano) announces the introduction, expected in May 1966, of the GE models U28B, U28C and U56. The short article states that while these models will be introduced at a 2800 HP rating, due to the limits of DC transmission (in particular generator size) GE was developing an AC/DC transmission to be employed at first in test units and then later in production locomotives (which we now know to all have been pre-production U30 units.) At that point, ALCO had developed, and EMD announced, 3000 HP units. What's important here is to note the concurrence in development of the 2800 HP powerplant and the 3000 HP powerplant, and considering the lack of any hard data in our mountain of manuals to indicate that other than governed speeds and fuel rack settings there's a difference of any significance between the "C" and "D" engines, we'll have to assume they were just different designations for essentially the same engine.
The sales brochure we have for the U30 actually for once mentions engine model by name, calling the engine "FDL-16D." Interestingly, the brochure also says that the engine's fuel-air ratio was properly maintained by monitoring the engine air supply - but we cannot find any such indication in either the Diesel Engine manual for the U30 (we have several, the earliest being GEJ-3847 printed 3-67) or the Educational Manual for the U30 (our earliest being GEJ-3849, printed 4-67.) This sounds like either a reference to an early two-slope pressure-bias engine control governor or to the overspeed / derater link which both actually appeared on production "E" engines, which we'll describe shortly. The sales brochure is, by the way, GED-5646 dated 2-67.
A large number of changes were introduced with the "E" engine. Following the introduction of the "E" engine, the same engine was used for both the new U33 locomotives and for the already in-production U30 locomotives. Up until this point, GE had dropped lower horsepower models when higher power units were developed, but popularity of the U30 caused it to remain in production alongside newer models. Thus, while the U30 began production with the FDL-16D, it progressed to the FDL-16E and later even the FDL-16F all the while being rated 3000 HP for traction. This may be the root of the old railfan saw that says that all GE models were alike except for fuel rack settings, but as we see now the situation was far more complicated.
FDL-16E This engine was that developed for production use at about the time the U33 was introduced, and apparently it included a very large number of test-proven developments GE had been working on in a wide variety of areas. We will not attempt to list these in any specific order but will use first the U33 sales brochure we have, printed 11-67 to hit key points that GE thought worth advertising heavily.
The "E" engine finally did away with the original overspeed protection system, in which an overspeed governor caused, on trip, a butterfly valve to shut in each intake manifold to cut off intake air. On the "E" and later engines, an overspeed - derater link is installed in the linkage between the governor control arm (or mechanical output) and the fuel rack linkage. On this device, trip of the overspeed governor will dump oil from this large, more complicated than it looks inside than out, coffee-can shaped link device causing it to expand under its own spring pressure (which the governor oil was overcoming) and pull the fuel rack linkage in the "less fuel" direction. This motion is enough to kill the engine. With oil pressure applied the device was a simple mechanical link. The other function of the device was to derate the engine if intake manifold temperature was too high (signaling a turbo problem, or plugged intercoolers, etc.) Wax filled actuators, inside the unit and supplied with a bleed of intake air, served to expand the actuator and reduce fuel rack setting if intake manifold temperature was too high.
The "E" engine also included a two-slope pressure-bias load control scheme governor, which simply means in GE parlance that the governor was able to control load on the engine, and fuel rate if needed, based on the actual intake manifold pressure. This both reduced engine wear and reduced smoke. The governor was set up so that if limit were needed, the load regulator would be operated to reduce load before the governor acted to reduce actual fuel rate. This type governor was capable of reducing both to the point that engine operation with a totally failed turbocharger was possible without engine overheating.
It appears that on the "E" engine, the Elliott H581 turbocharger was replaced with the Elliott BCO65, and that intercooling capacity was increased. A new cam profile was introduced on the "E" engine, according to the sales brochure: "New valve timing and new high-lift cam contour to improve engine breathing and reduce temperatures." On the fuel side, a new high-capacity fuel pump was included and this forced a change in the engine frame deck design to accomodate it. This is always called the "large fuel pump" or "large style pump" in GE literature. Engines were now also set to use a lower fuel header pressure (33-37 psi tolerance for old 'small fuel pumps' with the new "E" "large" pump system using a fuel header pressure of 22-24 psi.)
THAT'S IT for this installment. In the next, and final, installment we'll detail the upgrade to the "F" engine, and some later changes as well as trying to detail the confusing and non-matching progression of FDL-12 model numbers.