Steam vs Diesel HP

I know steam engines are not measured in HP but if the comparison was made between some of the old steam to diesel engines, what would be equal? Such as these for example:
4-8-8-4 Big Boy
2-6-6-6 Allegheney
2-8-4 Berkshire
4-4-0 like the Jupiter time
3 truck shay

or vice-vera
AC6000CW
AC4400CW
D9-40CW
SD45
SD40-2
GP40-2
GP7
F7

If these were compared to their opposites, what type would be what?

IIRC, the Big Boy was rated at approximately 6600 hp, That should be roughly equal to the AC6000CW. The Berkshire was well over 4000 hp, and the SD-45 is 3600 hp.

Occasionally, when preserved steam locomotives are run around people who know diesels, someone compares them. I remember two comparisons that got into print.
(i) EMD put some money into the American Freedom Train project in 1976, and so had people involved. A report in (I think) "Trains" quoted an EMD person as saying that the (ex-SP 4-8-4) used was, when it came to running the train at a good speed over various grades, equivalent to two and a half E-8 (so: to diesel locomotives rated 5625hp). Caveat: this was at speed. When it comes to starting the train from a dead stop, big 4-8-4 typically had a tractive effort of around 60,000 pounds. Two and a half E-8 would pull about twice that.
(ii) An ex-NKP Berkshire was run on a CSX line; CSX assigned a B36-7 to help. I don't remember the details, but apparently there were times on a run when each locomotive did the work. A story in "Railroad Model Craftsman" said that ONE B36-7 wasn't equal to the Berkshire.
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When the SD70-MAC was introduced, one historically-minded EMD person said that they "finally" had a single unit that could out-pull a (Norfolk & Western) Y6b (the final best 2-8-8-2 mallet): I think this was a tractive effort comparison, not horsepower.
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Early in dieselization, the New York Central did a carefully planned comparison of its "Niagara" 4-8-4 with EMD E-7 on Croton (New York) to Chicago passenger trains, famously finding the costs very similar (but maybe stacking the deck a bit by choosing test runs EXACTLY taylored to the steamer's characteristics). The Niagara significantly outperformed two-unit E-7, and was similar in performance to a three-unit E-7. The Niagara's horsepower (New York Central tested its locomotives very carefully) was over 6,000 "indicated" (basically power produced at the cylinders) at its best speed: power at the back of the tender was (i.i.r.c.) either 5300 or 5100 at best speed. (Steam locomotives only produce peak horsepower in a comparatively narrow range of speeds: one of the selling points of the diesel was that it could use full power over a broader range.) A three-unit E-7 is rated at 6,000 hp, under the (American) convention that the power of a diesel locomotive is the power the engine delivers to the main generator: with first and second genereation diesels, the train-pulling power was about 83% of the rated power: 4980.
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I vaguely recall seeing an estimate of about 500hp for a mid-19th century 4-4-0. Trains were much lighter then!

Cant compare withotu knowing hte speed. Speed matters steam puts out less hP al low speed deisel falls off as speed increaces. Learne this years ago.

Very interesting Allen.

Bystander is right.
Power (drawbar power: higher ratings just include power that is lost in the engine and transmission of the locomotive itself) is proportional to drawbar tactive force times speed. A (conventional) steam locomotive has the engine (the cylinders) directly connected to the driving wheels (or geared to them in a Shay: but even a Shay has a constant gear ratio, with no "clutch" for gear shift), so in a steam locomotive operating at low speeds the engine is operating at too low an rpm to generate full power. Result is that a typical steam locomotives power increases with speed up to an optimum which, in a well-designed locomotive, is in the speed range you hope the locomotive will operate in most of the time.

Because of the direct connection, a steam locomotive's engine starts "under load": starting from a dead stop, the piston has to exert full force immediately. An internal combustion engine would stall if you did this, so a diesel locomotive needs a transmission: the generator and traction motors in a diesel locomotive. Well designed, then, a diesel locomotive will have about the same power at any speed (except for very low speeds where full power would produce a force that would slip the wheels).

I have read that EMD's designers (Dilworth the head of the team) had in mind, in designing their original 1800 hp passenger units, the goal that a pair of them should be the operational equivalent of a good modern late 1930s passenger steam locomotive: I think New York Central's J-3 Hudson was one of the examples they had in mind. My guess is that at 85mph, pulling the 20th Century Limited across the flatlands of northern Indiana, a J-3 might have been putting out a bit more power than a pair of early E-units, but that (even with a booster engine on the trailing truck) it wouldn't be able to develope anywhere near their power at lower speeds. Since even the Century made some station stops, and so had to accelerate up to full speed several times, I'm not sure whether the slightly higher power of the J-3 at top speed would make up for its lower power at low speed.

I think some very important factors that demonstrate how steam and diesel locos DIFFER have been brought up. The biggest being the differance where a steam loco produces highest horsepower at higher speed, versus a diesel that produces highest power at low speed. I recall reading about when the US Army's MRS operated in Iran during WWII. The MRS found that pairing a 2-8-2 with an Alco RSD1 often acheived better performance than either an MU set of RSD1's or a double headed set of 2-8-2's.

FCP503--
I also remember reading that (about RSD-1 + 2-8-2 being better than either two diesels or two steamers in Iran) somewhere, but don't remember where: was there once an article in "Trains" about the WW II operation of the Transiranian?
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I've often fantasized about combining steam and diesel effectively. It is possible to rig up machinery that will translate a steam locomotive's throttle movements into m.u. signals to control a trailing diesel. (According to a "Trains" article in, I think, the 1970s, the Clinchfield did this on their ancient preserved 4-6-0 so it could lead the diesels that did most of the work on their Christmas-time specials.) I don't think it takes really HIGH tech to do this: in the late 1940s there were probabgly lots of veterans who had learned enough electronics in a wartime Navy training school that they could have designed the "interface.") It seems to me that a large railroad (large enough to sponsor somebody to design the equipment and then test and de-bug it) could have saved a fair bit over the years of steam-to-diesel transition by installing such equipment on its newer steam freight power.

In operation: couple a freight B-unit (if you're an Alco fan, specify that it should be an FB-1) behind the tender of a 4-8-4 or 4-8-2. (Depending on your favorite railroad, imagine any freight-service 4-8-4, or somethingly like a PRR M-1 or New York Central l-2/L-3/L-4 Mohawk.) At speed, the steamer would be doing three quarters of the work, but at low speed (starting up, recovering speed after getting a yellow signal, going up a hill) the diesel would about double the tractive effort. Advantages: MUCH cheaper than buying a 4-unit freight diesel (and the locomotive builders were working at capacity in the late 1940s/early 1950s: it wasn't possible to dieselize totally overnight), lighter weight than a new and bigger steam locomotive would have been (track maintenance and bridge departments would have fits if they thought you wanted to run Big Boy or a Pennsy Q-2 on most lines!): since the booster can be uncoupled, you don't even have to install longer turntables at your roundhouses!

Allen Hazen wrote:FCP503--
I also remember reading that (about RSD-1 + 2-8-2 being better than either two diesels or two steamers in Iran) somewhere, but don't remember where: was there once an article in "Trains" about the WW II operation of the Transiranian?
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I've often fantasized about combining steam and diesel effectively. It is possible to rig up machinery that will translate a steam locomotive's throttle movements into m.u. signals to control a trailing diesel. (According to a "Trains" article in, I think, the 1970s, the Clinchfield did this on their ancient preserved 4-6-0 so it could lead the diesels that did most of the work on their Christmas-time specials.) I don't think it takes really HIGH tech to do this: in the late 1940s there were probabgly lots of veterans who had learned enough electronics in a wartime Navy training school that they could have designed the "interface.") It seems to me that a large railroad (large enough to sponsor somebody to design the equipment and then test and de-bug it) could have saved a fair bit over the years of steam-to-diesel transition by installing such equipment on its newer steam freight power.

In operation: couple a freight B-unit (if you're an Alco fan, specify that it should be an FB-1) behind the tender of a 4-8-4 or 4-8-2. (Depending on your favorite railroad, imagine any freight-service 4-8-4, or somethingly like a PRR M-1 or New York Central l-2/L-3/L-4 Mohawk.) At speed, the steamer would be doing three quarters of the work, but at low speed (starting up, recovering speed after getting a yellow signal, going up a hill) the diesel would about double the tractive effort. Advantages: MUCH cheaper than buying a 4-unit freight diesel (and the locomotive builders were working at capacity in the late 1940s/early 1950s: it wasn't possible to dieselize totally overnight), lighter weight than a new and bigger steam locomotive would have been (track maintenance and bridge departments would have fits if they thought you wanted to run Big Boy or a Pennsy Q-2 on most lines!): since the booster can be uncoupled, you don't even have to install longer turntables at your roundhouses!

i love this idea steam with diesel booster B unit

I love this idea steam with diesel booster B unit

Me too. Doesn't the Grand Canyon Railroad sometimes do this?
One of David Wardale's idea was to cut two or three diesel units into the middle of a freight train to help with starting and hill-climbing. They would make excellent retarders too with their regenerative brakes. On level stretches a modern steam loco would have to take over the lot as it pollutes much less.