General Electric U-Series Manufacturer Data

[Typewriters]

For those interested in manufacturer information on the historic Universal series locomotives, I've started this new string. Allen Hazen should be particularly interested.

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7FDL-16 Engines / Domestic U-Series

The 7FDL-16 engine had subletters to designate models, and numbers following that to designate variants. From the 1977 UX (Unit Exchange) manual we find the following listed model information for Domestic (United States) Universal series road locomotives only.

U25: 7FDL-16A2, A3 and A5

(Note: Other materials in my collection tell us that there were more variants; these are probably just those that GE was offering replacements for, The hint here is that A1 and other variants may have been deleted from locomotive fleets and replaced with variants as seen here. Also, the very first advertising brochure for the U28 described the diesel engine for that series as the 'latest improvement on the 7FDL-16A3 engine, but it's clear that GE decided to redesignate the new single exhaust pipe, steel cylinder head insert engine as the C series.)

U28: 7FDL-16C1 through C8

U30: 7FDL-16D1 through D7

(Note: After the U30 had been in production for some time, the U33 appeared. From that point on, U30 and U33 locomotives received variants of the same engine in the E series.)

E Series Engines

U33: 7FDL-16E1, E2, E3, E4, E5, E9, E10, E12, E14, E15, E16, E17, E20

U30: 7FDL-16E6, E7, E8, E11, E13, E18, E19, E21

F Series Engines (U34 and U36)

U36: 7FDL-16F1, F3, F5

U34: 7FDL-16F2, F6

G Series Engines (U30, U33, P30) These are the CHEC excitation engines, with unique components.

U30: 7FDL-16G1, G3, G6, G7, G8, G9

U33: 7FDL-16G2, G4, G5

P30: 7FDL-16G6

H Series Engines (3600 HP CHEC excitation)

U36: 7FDL-16H1, H2


The 12 cylinder engines do not appear to follow the 16 cylinder engines, as I've noted before, in chronological sequencing and letter application. The domestic U23 series and the U50C have engines in various 7FDL-16C, D, and F series. The specific engines for the U50C were the 7FDL12D1 and 7FDL-12D4.

REBUILT ENGINES offered by GE were sourced from the pool of traded in engines and/or engines submitted for the Unit Exchange program. The program was complex, but basically operated this way: Owners of fleets who wished unit exchange for six units or more could obtain engines rebuilt at GE in the UX series, and send in their own engines as trades. In this "normal" form of the program the owner DOES NOT receive back his own engines rebuilt, but rather engines from the program. There was provision to have an owner's engines sent in and rebuilt as well.

Rebuilt engines were built to a given "replacement standard" designated by GE, which in most cases included upgraded components - either because the original components were out of production, or because the newer components were more compatible with more recent production (which eases spare parts supply.) So, for example, several of the rebuilt variants offered as straight replacements for engines for the U25 series incorporated steel crown pistons which in actual chronological production had not appeared until the introduction of the F engine for the U36. (Steel crown A series replacement engines were the 7FDL-16A3R2, 7FDL-16A3R3 and 7FDL-16A3R5.) Speaking still of replacement engines in the A series, GE listed the A3R5 variant as the Primary stock model, with the A3R1 occasionally in stock. The other variants (2 through 4) would be built upon request. These had varied other features.

It is worth noting that GE was not offering in the rebuilt A series engines, apparently, the original true "one piece" cylinder assembly. All that were being turned out were the steel cylinder head insert type that had originally appeared with the preproduction U28 locomotives and became the 7FDL-16C series in domestic U-boats. I will have to look, but recall seeing in an engine overhaul manual the mention of the eventual non-availability of the original A series style assemblies and provision for substitution of the C or later type when railroads were ordering replacement parts.

Anyway, that's enough for now. I have lots more to add in further posts that'll go into the various rebuilt engine packages. Also there'll be posts on other equipment through the U series line as I dig it out of the pile of manuals I've got around here.

For those unfamiliar with the FDL model designations I suggest the four part series I did years back on our locomotive blog. Search for the FDL engine articles: http://railroadlocomotives.blogspot.com/" onclick="window.open(this.href);return false;

-Will Davis

[Typewriters]

FUEL PUMPS 7FDL-16

Previously in material I'd written ( http://railroadlocomotives.blogspot.com ... ent-3.html" onclick="window.open(this.href);return false;) I referred to the replacement of the original "small" fuel pumps (as GE later called them) which were applied to the 7FDL-16A, C, and most D series engines (U25, U28, U30) with the large style that was used then for a number of years. The UX rebuilt manual now gives us specific information.

The change to the "large" fuel pumps occurred with the 7FDL-16D7 engine variant, and this occurred (vaguely as expected) in 1968. Interestingly there is also reference to a change in master connecting rod design concurrent with this change to the "large fuel system," as GE states that it does not warranty the older "studded cap" master rod type if used with any engine having the large fuel system.

Once the large system was put in production both the injection pumps and the nozzles were sourced from both Bendix and Bosch; Bosch equipped engines would have an "AB" suffixed to the engine model number on the ID plate.

All of the rebuilt UX program engines offered in the A, C, DC, and D series are listed with the small fuel system. DE, E, F and G engines have the large fuel system.

There are NO dual letter engines as original equipment. The DC and DE series appear to be modifications that were built to allow adaptation of a given set of engine parameters to be fitted into other locomotives. For example, when we look at the table listing locomotives that originally had E series engines (U30 and U33) we find that the recommended rebuilt engines for the U33 units are in the E4R series, while those for the U30 are in the DE4R series.

-Will Davis

[NorthWest]

Thank you and welcome back! This is a lot of interesting information.

It is interesting that the U34CH has the F6 engine when its production preceded the U36C which had the F1-F5 FDLs.

[Allen Hazen]

Re: "Allen Hazen should be particularly interested."
He's very interested (and grateful!)… and will take a while trying to absorb all this.
I take it that actual dates of introduction of the various subtypes are not readily ascertainable?
How about the introduction of the CHEC excitation? One source I have says that U34CH production ended in 1/73. (I don't think this includes the unit rebuilt from a C&NW U30C…) Since your list does not show U34CH as having CHEC engines, I'm guessing that CHEC dates from 1974-74 or so: in which case only the last SP U33C would have had G-series engines, and only the last U36C would have had H series, along with, maybe, the very last U36B. (***If*** the final U36B had CHEC… Conrail must have been overjoyed having a new engine subtype and control system on four units!)

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I would assume that continued engine improvements in the Dash-7 to Dash-9 period led to further subtype designations. So, the real reason (Grin!) for the switch to the GEVO engine was that GE had run out of letters to suffix to FDL subtype designations! (Compare: U25B prototypes to end of domestic U-series production was 19 years, with five ratings for the FDL-16. Beginning of Dash-7 production to beginning of production of production GEVO units was 18 years, with at least five new ratings for FDL-16 equipped units: 3750, 3900, 4000, 4135, 4390.)

[Typewriters]

Thank you and welcome back! This is a lot of interesting information.

It is interesting that the U34CH has the F6 engine when its production preceded the U36C which had the F1-F5 FDLs.

Note that the first U36 variant is 7FDL-16F1 and the first U34 variant is 7FDL-16F2.

There's no question that the F series engine was originally developed as a 3600 HP for traction engine. The first U36B units were built May 1970, while the U34CH appeared in October 1970. For whatever it's worth, I'd bet GE 301-304 were operating at 3600 HP prior to these dates.

The old saw that the U34 preceded the U36 is just another error from the old Kalmbach universe, who forgot that the four axle U36 made it into production months before the six axle U34CH. Also, let's remember that the same general source was putting out that the U34 "predicted the later steel cappped pistons of the U36," but I have evidence here now that the steel capped piston appeared in 1970 (according to GE materials) so that it may simply be that the U34 was the first order out of the factory to incorporate steel capped pistons in F series engines, and that the next U36 units built also had them. There's nothing to indicate they were developed for or because of the U34's somewhat unusual engine speed schedule as compared with normal units.

-Will Davis

[Typewriters]

Re: "Allen Hazen should be particularly interested."
He's very interested (and grateful!)… and will take a while trying to absorb all this.
I take it that actual dates of introduction of the various subtypes are not readily ascertainable?
How about the introduction of the CHEC excitation? One source I have says that U34CH production ended in 1/73. (I don't think this includes the unit rebuilt from a C&NW U30C…) Since your list does not show U34CH as having CHEC engines, I'm guessing that CHEC dates from 1974-74 or so: in which case only the last SP U33C would have had G-series engines, and only the last U36C would have had H series, along with, maybe, the very last U36B. (***If*** the final U36B had CHEC… Conrail must have been overjoyed having a new engine subtype and control system on four units!)

--

I would assume that continued engine improvements in the Dash-7 to Dash-9 period led to further subtype designations. So, the real reason (Grin!) for the switch to the GEVO engine was that GE had run out of letters to suffix to FDL subtype designations! (Compare: U25B prototypes to end of domestic U-series production was 19 years, with five ratings for the FDL-16. Beginning of Dash-7 production to beginning of production of production GEVO units was 18 years, with at least five new ratings for FDL-16 equipped units: 3750, 3900, 4000, 4135, 4390.)

Allen... Thanks for the reply!

There are not dates of introduction, etc. in this book as it's essentially a parts, ordering and procedure manual. So we need to use this information melded with other clues from other places to get the whole picture.

I am thinking that CHEC excitation is part of the range of "1975 improvements" which GE integrated into the line prior to the introduction of the "New Series" or Dash 7 locomotives. It also MAY be true that CHEC was backfitted to earlier models. Later CHEC equipped turbochargers can be used on non-CHEC locomotives however with no problem - the CHEC probe just is not connected to anything.

There was a CHEC-1 system used on Dash 7 units that incorporated CMR wheelslip and employed traction motor transition. The CHEC-2 system was applied to later units that had the double winding alternator, thus made alternator transition.

GE by all appearances abandoned the subletter designations eventually, and just refers to the engines by the 7FDL- with the number of cylinders. I will try to figure out exactly when that break occurs. I believe I have that here somewhere.

-Will Davis

[Typewriters]

FDL LETTER DESIGNATIONS DISAPPEAR

Looking more into Allen's question about FDL engine designator letters, we find a sheet in a GE Locomotive Engine School binder here with a date of June 1983 that spells out engine models and some of their parameters such as horsepower, notch 8 speed, size of injection pumps and injection timing.

Here, we only see letter designations applied up through F. None of the -7 or -8 locomotive listings has any subletters by their designators. Of course we know from the UX manual that there were G series engines (CHEC excitation) but this letter isn't seen in this table. We might then easily suspect that GE dropped the letter designators for new locomotive engines soon after the "New Series" or -7 locomotives were introduced.

FDL ENGINE SPEEDS

An interesting fact pops up in this table. As we know, the U30 introduced the D series engine. When introduced, the D ran at 1025 RPM in notch 8. The U30 continued on into the E engine series and initially the U30 units with E engines ran at 1025 RPM as well. However, the E series appeared concurrent with introduction of the U33 series, and the E series in the U33 ran at 1050 RPM from the start.

At some point the U30 locomotives using E series engines changed their speed schedule so that they matched the U33, with N8 speed being 1050 RPM. The F engine for the U36 also ran at 1050 RPM full speed.

Considerably later, GE performed studies (which I have record of elsewhere) that showed how much horsepower they were losing to friction by running at these engine speeds and the company began studies to toughen the engine to take much higher firing pressures at lower RPM's. This is reflected in the table. While the B36-7, C36-7 and B30-7A are listed as having N8 speed as 1050 RPM there is another line for other C36-7 having a 1000 RPM engine speed (back down to the speed of the U25 and U28.) The B32-8 and C32-8 are shown up at 1050 RPM, but the B39-8 and C39-8 are shown at 1000 RPM too, consistent with the change to reduce friction losses in the engine.

A 1991 insert elsewhere in the manual lists full engine speed being back up at 1050 RPM for 8, 12 and 16 cylinder engines. This triggers a look at the Diesel Engine Adjustments section dated 1993....

We find the engines in all the very modern 12 cylinder units (B32-8, C32-8, 8-32B and 8-32C) running 1050 RPM in N8.

The B32-8 and C32-8 are listed at 3150 HP for traction.

The 8-32B is listed at 3210 HP for traction; the 8-32C at 3180 HP for traction.

The B39-8, C39-8, 8-40B and 8-40C run at 1000 RPM. Horsepower for traction on these units is as follows:

B39-8: 3900
C39-8: 3900
8-40B: 4020
8-40C: 3990

The 8-41B and 8-41C are listed at 1000 RPM and 4135 HP for traction.

Finally engine speed comes back up on the 9-44B and 9-44C units, 1050 RPM and 4380 HP for traction.

The difference of about 30 horsepower for traction between a couple of the four and six axle types is interesting.

-Will Davis

[Typewriters]

TWO PIECE CYLINDER ASSEMBLIES BECOME UNAVAILABLE

The original U25 locomotives were built with what GE would later call the "original, two piece" cylinder assemblies. These had a large casting into which a removable cylinder liner was inserted.

Introduction of the C series engine (2800 HP for traction, 3050 HP gross at 1000 RPM in 16 cylinders) also brought with it the "three piece" cylinder assemblies. These incorporated a removable steel cylinder head unit inside the cylinder, in which the valves were mounted. GE continued parts support however for the original style after introduction of the C engine into general production in 1966.

Looking at the UX manual (the Unit Exchange manual) we see in Section 110 / Diesel Engines, Table 5 the footnote that "Two-piece cylinder assemblies, Part Numbers 121X1046 and 121X1057" are listed under the heading that says "The following equipment is no longer available on Unit Exchange engines. These components may be removed from engines before return." Also included are the U25 style multiple pipe exhaust manifolds and the corresponding turbocharger inlet casing for the 16 cylinder engines. No specific date for dropping them is given, but we know for sure it's before the 1977 date of the manual.

Now, this isn't to say that parts support for the U25 was dropped at this point in this respect. GE was listing at this same time five Unit Exchange diesel engines for the U25 series locomotives. Some had original style cast iron pistons, some had steel crown. All would have had a newer style cylinder assembly with steel cylinder head. All would have had the single pipe (constant pressure) exhaust manifold that the C series introduced. Some had the old 45 degree inlet valve seat angle while two had the new 15 degree angle. Some had chromed cylinder liners, some the Tufftrided liners.

The important thing with the UX program is this: A railroad, upon signing a contract for UX engines, would send back to GE the engines that it was trading in within 30 days of receiving the reconditioned UX engine from GE. The railroad was then invoiced for the amount required to get the traded-in engine back up to the standards of the engine that had been delivered by GE. So, trading in a fully worn out FDL-16A engine with many parts that might not be suitable for repair and reconditioning might quickly prove expensive. The manual seems to imply that the Limited Repair and Return option might be more economical in some cases. Whatever the case, it seems obvious that the more old parts that went out of production the higher the UX cost for swapping out early U-series engines. That may well have made a better case for trading in the whole locomotive on a new unit.

-Will Davis

[Allen Hazen]

Still trying to absorb. (Grin!)
This is great stuff: thankyouthankyouthankyou!
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Re: "The difference of about 30 horsepower for traction between a couple of the four and six axle types is interesting."
Indeed. I noticed this difference back when the first Dash-8 prototypes were announced in 1984 or 1985. (I think one article or news item actually referred to the three 12-cylinder, 4-axle units in BN colours as "B32-8" and the ten 12-cylinder, 6-axle units as "C31-8", but I could be misremembering.) I would assume the same basic engine is involved, so the "raw" horsepower should be the same, so a difference in "horsepower for traction" would have to reflect a difference in parasitic load -- my impression is that this was being calculated very carefully: many of the Dash-8 innovations were aimed at improving fuel economy. Could it be that traction-motor ventilation takes 15 horsepower per motor? So that the 30hp difference in traction horsepower between, e.g., the B32-8 and the C32-8 is accounted for by having to "blow" cooling air at two more motors?

[Allen Hazen]

Re my last speculation, about why C-something-8 locomotives might have had less power for traction than their B-same-something-8 analogues: I think I'm at least in the right ballpark for traction motor blower power requirements. (At least in the U-series, GE diesels did not have separate traction mower blowers:ventilation air was provided for both traction motors and above-deck equipment by the central equipment air blower. But.)
This
https://en.wikipedia.org/wiki/Indian_lo ... lass_WAG-7" onclick="window.open(this.href);return false;
article is about a class of Indian electric locomotives: six-axle, six motor. Traction motors seem to be a Hitachi design, but comparable in per motor output to the late 752 motors on Dash-8 locomotives, and of the same general sort (nose suspended). So ventilation requirements might have been roughly similar. These locomotives have two traction motor blowers, each with a 35hp Siemens motor: so, traction motor ventilating air seems to have been blown by 11 2/3 hp per motor.

(Dash-8 locomotives, as part of their general fuel efficiency strategy, could deliver more traction power at times when the parasitic drag was less. I'd guess that GE's figures, here, are conservative: the guarantee able traction horsepower, which the locomotive might occasionally be able to exceed. But anyway, I would think it likely that maximum traction motor cooling air would be required at many of the same times as maximum traction power. So 15hp/motor for traction motor air seems PLAUSIBLE as a conservative estimate.)

(Typewriters already knows about me, but newcomers to the conversation are pointed to the word "speculation" in the above, and the "I'd guess" and "seems PLAUSIBLE".)

[Typewriters]

Allen,

I think what you're proposing is wholly plausible. Good show.

-Will Davis

[MEC407]

Mr. Davis, thanks so much for sharing this information with us! Bravo!

[Typewriters]

GE "TWO LEVER" CONTROL STAND / KC-102 CONTROLLER

Folks, this post will in all probability be supplemented at another point by a blog post, since a couple of the resources I thought I could link to at George Elwood's Fallen Flags site have been taken down or just aren't there. We'll get something out of this though.

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General Electric's domestic U-series locomotives, from the very first U25 units, used the KC-99 master controller. This is the one with the usually monstrous throttle lever, whose tough operation has been complained about before (remember the engineer on here who told us he'd remove the pawl spring, then put it back at the end of the trip?) This controller and its familiar style of control stand, easily found in internet photos, continued for all U25 and U28 locomotives (and included the U50 for UP and SP) and was put in the U30 as well.

As we know (from information found in one of our Railway Fuel & Operating Officers' Society convention books) GE did get the message that this throttle was somewhat disliked, and it developed what it called "a short, easy to operate throttle."

Recent information I've found, put together with a lot I already had, confirms for us beyond doubt that this is in fact the KC-102 model master controller. This is found in the GE "two lever" control stand.

This controller appeared, at my best guess, right at the start of 1968. This makes the inclusion of this controller concurrent with the introduction of the U33 series, more or less (although I do suspect perhaps the very first few production U33B units had KC-99's.) This also marks the moment in time that the U30 changed from being what it had been at introduction to essentially a derated version of the U33, with smaller radiator cores and a different governor and engine speed schedule being the key differences -- of course, the excitation system cards were different as well.

The KC-102 controller had several submodels.

One of them had a 16 notch throttle and a five position reverser/selector for use with dynamic brake equipped units. The throttle had physical notches in both motoring and dynamic braking.

Another had the 16 notch throttle and only a three position reverser, as it was for units that did not have dynamic brakes.

Another had the 16 notch throttle and the five position reverser/selector as with the first variant, but added a further mechanical interlock on the reverser/selector in form of a spool on the shaft, or collar, that had to be moved back to allow the lever to enter either dynamic brake position. Of course as with all the others it was still interlocked with the throttle and couldn't be moved unless the throttle was in 'idle.'

A fourth version had an eight notch throttle, not different from the other in physical form but connected to a drum that only had contacts set up for an eight notch unit. The selector lever on this type was the five position kind, and in dynamic brake it knocked out the latch pawl on the throttle. Thus, in dynamic brake, after a 'setup' notch (actually corresponding to the old 1/2 position on the 16 notch throttle) movement of the throttle was smooth all the way up to full braking.

Now, these above are the facts. We can assure you that the last mentioned throttle type is that which was actually used on the Union Pacific's U50C units, but I cannot hazard a guess as to any others. We do know that 1969 publications by GE begin to say "late model locomotives have only eight notches," so that the time window for the 16 notch KC-102 variants is only a couple of years.

The key discovery was the purchase of a big GE manual covering the tiny fleet of U30C units built for Colorado & Southern, in 1968. I knew it was the right time frame, and went for it. It has added very much to our knowledge already.

MANUALS

Those looking for a GE operating manual showing this stand will have a rough time. The only one is the original GEJ-3856 (note no subletter) which is the first ever domestic U series manual to cover a range of models and horsepowers. My example was published 2/68 and since it's the only one I've seen, I will have to go with that date now. It's a good date to cover the earliest production U23 and U33 units. The A variant of the manual is unknown, but the GEJ-3856B variant published beginning in 1972 is quite common. This is the one that shows either the AAR compliant KC-108 controller or else the EMD two-lever ratchet selector controller sometimes ordered as an option. This all gives us a boundary of dates again, roughly the start of 1968 through to 1972 when the AAR compliant controller became standard in GE U-series domestic units, for the KC-102 to have been fitted.

There's a lot more to share, including illustrations of the controller and even its internals, but I need to make photos and get a blog post together. That will be a brief version of what I've gone into here, but it will have photos. Until then, see how many photos of the KC-102 two-lever stand you can find on the net. It isn't many, I assure you!

-Will Davis

[Pneudyne]

The KC-102 controller had several submodels.

One of them had a 16 notch throttle and a five position reverser/selector for use with dynamic brake equipped units. The throttle had physical notches in both motoring and dynamic braking.

The use of notched dynamic brake control in this case was probably because of the form of exciter battery field control that GE had adopted originally for its U25B model, as described in the GE U25B Educational Manual, GEJ-3815.

The exciter battery field was controlled, in both motoring and braking, by a resistor ladder switched in 16 steps from the throttle handle. The output from this resistor ladder was supplied to both the local exciter battery field (via the load regulator rheostat in motoring) and to the dynamic brake control trainwire (XB). Any trailing GE U25B units had their exciter battery fields supplied from the XB trainwire in both motoring and braking, being conditioned so to do by energizing of the MR trainwire, which was basically how a leading U25B let any trailing units know that it was leading.

When a U25B was trailing in a consist led by other than a U25B, the MR trainwire was not energized. In that case, motoring excitation control was done locally using the AV, BV, CV and DV throttle-notch trainwires to switch the excitation steps. Dynamic brake excitation control was done by the load regulator rheostat under the control of a positioner relay fed from the XB trainwire in conjunction with the governor overriding solenoid. Perhaps ironically, the last-mentioned approach to potential-wire dynamic brake control, that is using a positioner relay, appears to have been an EMD invention, developed for its export locomotives and covered by a patent as noted in the EMD dynamic brake thread, viewtopic.php?f=6&t=152156" onclick="window.open(this.href);return false;.

What comes out of this is that in the U25B, the XB trainwire not only supplied the reference voltage for potential-wire dynamic braking control, as would be expected, but it also supplied excitation power for motoring as well as for braking, to any trailing U25B units in a consist.

The KC-102 controller had several submodels.

A fourth version had an eight notch throttle, not different from the other in physical form but connected to a drum that only had contacts set up for an eight notch unit. The selector lever on this type was the five position kind, and in dynamic brake it knocked out the latch pawl on the throttle. Thus, in dynamic brake, after a 'setup' notch (actually corresponding to the old 1/2 position on the 16 notch throttle) movement of the throttle was smooth all the way up to full braking.

This was a reversion to the traditional, continuously variable form of dynamic brake control for diesel-electric locomotives. Possibly GE’s thinking was whereas 16 steps provided sufficiently fine dynamic braking control, 8 steps did not, so that the overlap of the motoring and braking control functions that the U25B had enjoyed was no longer appropriate with an 8-notch throttle.

That kind of difference between motoring and braking control had applied to GE’s export Universal models of the later 1950s, as described in an article in “Diesel Railway Traction” magazine for 1959 December. In these, motoring excitation was controlled in 8 steps by a resistor ladder switched from the AV, BV, CV and DV trainwires. Braking excitation was controlled in a continuously variable manner by a rheostat in this case operated by the selector handle rather than the throttle handle. These had KC92H (right-hand drive) or KC92J (left-hand drive) control stands. Although some later exports were fitted with newer controller types, the KC92 seems to have been used through the 1970s at least.

Re the development of the GE 7FDL engine, I have a copy of 1982 GE paper, “Reliability and high specific output – an American manufacturer’s view”. This described the mechanical development of the 7FDL to that time. And although the development steps were not correlated with engine variant suffix numbers, the progression was described in terms of upwards steps in the key parameter mean effective pressure (MEP). The starting point was an MEP of 200 lbf/in² at 1000 rev/min, increasing to 282 lbf/in² at 1050 rev/min in 1970. In 1981 the 12-cylinder engine went to 307 lbf/in² at 1050 rev/min, followed by the 16-cylinder version to 296 lbf/in² at [the fuel economy speed of] 1000 rev/min. At the time that the paper was written, laboratory engines were running at 340 lbf/in².

And re traction motor blower power requirements, one datapoint I do have is for the British Rail 50 class, 2700 hp gross, probably around 2500 hp tractive. It had a pair of motor-driven blowers, each serving three EE538 traction motors (of about the same capacity as the GE752), and each driven by a 14.4 hp DC motor. Something to note is that motor-driven blowers, which operate at constant speed, could be quite a bit smaller than engine-driven blowers intended to do the same job. The latter need to have adequate capacity at lower engine speeds, and that probably translates into significant excess capacity at full engine speed. Power draw by blower fans follows the propeller curve, approximately cubic with respect to rotational speed. So for example, a blower sized to draw say 14 hp at 800 rev/min would draw close to twice that, say around 28 hp, at 1000 rev/min.



Cheers,

[Pneudyne]

Here is another datapoint in respect of traction motor blower power requirements, perhaps more relevant. It refers to the Alco DL-600B and DL-640, both 2400 hp, with respectively six and four motors. Both had a pair of engine-driven traction motor blowers. The combined power draws at full engine speeds were respectively 64 and 44 hp, a difference of 20 hp between the six and four motor variants. So this reinforces the idea that a 30 hp difference in motor blower power requirements for a later and significantly more powerful locomotive pair is quite plausible.

Cheers,