diminished horespower in rebuilds

[gabe]

I have a question for those in the know:

Maybe it is just me, but every time I hear about the major rebuilding of diesle locomotives (California & Arizona's SD-45's KBS's GP-38s being goood examples) the rebuild ends up with the engine being rated at less horsepower. Usually as a result of the removal of the turbo charger (but I am a novice in this area and, in all honesty, have only the vaguest idea of what that means and why it is important).

My question is: Isn't horsepower good? Why are engines considered improved after having less horsepower? Does reducing the horsepower lead to better fuel economy, maintenance or something? Very curious.

I understand that my comprehension of this subject is fascile at best, but please enlighten me.

Gabe

P.S. An even more mundane question: should the plural of "cabose" be "Cabese?"

[Overmod]

Reducing rated horsepower often has SUBSTANTIAL consequences for engine longevity, even for what appear to be very small changes. For example, engine life for some classes of diesel engine is dramatically longer at 900 max RPM than at 930. This doesn't seem like a lot, but with the large dimensions and mass of these engine parts, it's substantial.

In some cases, 'reduced horsepower' is done by taking cylinders out of 'service', as in some cases where SD45s were modified by leaving four of the 'holes' unfired. (Note how carefully I worded this -- do not assume that pistons and rods were removed, a different crank substituted, etc., as there were several different ways tried.). Naturally this gives a lower fuel burn from idle all the way to Run 8.

Removing the turbocharger cuts down on the ability to use a higher fuel-rack setting... you're limited to the amount of oxygen in a 'normal' charge, and consequently have a lower limit on how much fuel can be combusted with that oxygen without producing smoke instead of torque/HP. If your locomotive doesn't require the higher horsepower, there can be considerable maintenance savings by eliminating the turbo, its cooling and oil connections, etc. etc. etc.

Ask Randy Stahl and the other locomotive folks (I'm tempted to copyright this as a service under the name "Stahl et al." ;-}) for more specifics and detailed information.

[oltmannd]

Yes and Yes.

Yes, HP is good, generally, for mainline freight. The more HP/ton, the sooner you get to destination. However, the more HP/ton, the greater your fuel consumption.. So, assuming the goal is to move stuff from A to B as quickly as possible rather than at least cost, more HP is desirable.

Now, in the real world of railroading, there is a trade-off between performance and cost. Therefore, they are always looking for the right balance between performance and cost and maintenance and fuel are two of them.

When deciding what model locomotive to buy, RRs have two peformance issues, Tractive effort and HP. If they purchase the right ratio of these, they will have locomotives that will take their max tonnage up the railroad's ruling grade with out overpowering the train in terms of HP/ton.

The SD45 lost out to the SD40 in this regard because it didn't have any more max TE, and that extra 600 HP just wasn't needed to maintain required freight schedules. All it did was burn more fuel (higher HP/ton).

Now, if you are a shortline and you need to make one round trip a day with a max track speed of 25 mph, say, you really don't need much HP - just enough to get you out and back in a day. You do need enough TE to get you up the hills w/o stalling, though, so the extra 1000 HP of a GP40 over a GP38 is just wasted.

On the maintenance side of things - fewer parts is better. This applies to the number of parts in each locomotive AND the number of locomotives. e.g. 3 C40s can replace 4 SD40 w.r.t HP and TE. For a shortline, getting rid of the turbo is a big deal. It is very prone to failure from a multitude of causes and costs a bundle to rebuilt and install - particularly on EMDs. So, generally, de-turboing is a good idea.

[Randy Stahl]

I think the SD45 got way more bang for the buck than the SD40.. Think about it 600 more horse power from 4 more holes the sd45 is a great drag engine meant to stay in throttle 8. Problem is,, not alot of RR applications require this and when the locomotive is used for less strenuous work , the efficiency goes in the toilet. The SD45 s biggest problem was the long crankshaft that had a bad habit of snapping . I guess that became a regular occurance, I've seen many myself. I think the SD, in SD45 really did stand for special duty.
Cylinder blanking is a BAD idea, I don't know if it's ever been done but it would be impossible to get the engine in balence, it would shake itself to pieces, kinda like the 567C engines that have 645 assemblys installed because 567 parts are getting hard to find, those engines vibrate terribly. One shortline I consulted with had changed to 645 powerpacks and were very upset that the locomotive was coming unglued. A partial solution is to change the two camshaft counterweights, this helps considerably.
I can see wanting to get rid of the turbocharger, with a life expectancy of about 5 years, and a replacement cost not including labor $25,000.00. big expense!!!! If I were running a small RR on a tight budget I would fear all my turbos going at the same time!!!!
Randy

[Anonymous]

interesting...i never knew the turbo wasn't free-wheeling all the time. so it's basically a supercharger/blower/whatever, assuming belt driven, till notch 6 then?

[Randy Stahl]

I've never seen a locomotive working with any of the cylinders blanked, If someone is thinking about doing it please see me!
As for EMD turbo's they are gear driven off the gear train or generator end of the prime mover or two stage, GE & ALCO locomotives are only exhaust driven or single stage.
Randy

[oltmannd]

QUOTE: Originally posted by Randy Stahl

I think the SD45 got way more bang for the buck than the SD40.. Think about it 600 more horse power from 4 more holes the sd45 is a great drag engine meant to stay in throttle 8. Problem is,, not alot of RR applications require this and when the locomotive is used for less strenuous work , the efficiency goes in the toilet. The SD45 s biggest problem was the long crankshaft that had a bad habit of snapping . I guess that became a regular occurance, I've seen many myself. I think the SD, in SD45 really did stand for special duty.

EMD had pretty much solved the SD45's big problems with the SD45-2, but it still didn't sell. The reason was it had the same TE at MCS as an SD40-2 (about 83,000#), so it's drag tonnage rating (most tonnage it could take w/o stalling on ruling grade) wasn't any higher. It would just move the same tonnage a bit faster-and at a higher fuel cost.

Once the builders figured out a way to match the increased HP with increased TE, you had a marketable locomotive again. An SD50 has 15-20% more TE at MCS and HP (35/3600 HP and 96,000# TE) than an SD40-2. The SD60 and 70 DC and SD80&90MACs also have more HP and TE in about the same proportion.

When it comes to justifying the purchase of new locomotives, one of the two big drivers is replacement ratio. Most RRs found the same replacement ratio with SD40-2s the same as with the SD45-2s, so the extra cost for the 45 couldn't be justified. The other big driver is fuel cost - and the SD45-2 was at a disadvantage, here, too.

[oltmannd]

QUOTE: Originally posted by Randy Stahl


I can see wanting to get rid of the turbocharger, with a life expectancy of about 5 years, and a replacement cost not including labor $25,000.00. big expense!!!! If I were running a small RR on a tight budget I would fear all my turbos going at the same time!!!!
Randy

If I remember right, it takes about 70 man-hours to do turbo changeout in an EMD. Not cheap!

[CSSHEGEWISCH]

Some of UP's C30-7's indeed did use two of the cylinders in the FDL-16 engine as air compressors. I don't know how long that they remained equipped that way.

NS tried a more radical experiment with at least 2 GP9's in which only half of the cylinders were still firing. I believe that all sorts of problems ensued.

[Randy Stahl]

Yea thats about right..... We had some really good guys at the WC and had that time cut to around 35 man hours. The WC had a fleet of 20 cylinders and we found that they really weren't that bad on fuel, I think we had at one time about 106 of them and they would have bought more. with the bolt on adhesion systems like retro Em 2000s or Q-Tron these engines really shined. Our crews would reject the SD40s for the higher horsepower of the 45s. Remember that EMD returned to the 20 cyl in the SD80MAC... Can't be that bad. The 20 cyl will always have the stigma of the breaking crankshafts, the problem was never solved however they did improve with the X block or heavy block, With more interior bracing and thicker steel at least if you line bore the mains it'll stay .
Randy

[Randy Stahl]

QUOTE: Originally posted by M.W. Hemphill

Randy, can you recall a SINGLE instance of a 20-645 that had blanked cylinders -- that actually ran? I've heard talk of it, but cannot recall a single example that made it into service. I've never seen one.

There was, as I recall, an experiment of using two cylinders (I believe of a C30-7) engine as the air compressor. I never heard anything more about it, which leads me to believe it wasn't successful.

Good god.... I thought the GEs vibrated enough without doing something like this !!!!!!!!

[Anonymous]

I have spent a couple of hours searching but I can't find it again.

A year or so ago I came across a web page for a company that converts 20 cyl 645s to 16 cyl. They had a very nice page with pictures of the various steps and descriptions of everything.

"Blocking off" four cylinders, if ever done, wouldn't be as easy as it sounds, and may not be an improvement. You would still have friction of the mechanical parts and the pistons would be pumping air even if the valves were blocked open or removed and the manifolds were removed.

Using a cylinder as an air compressor is common in marine applications where it is also used as the starter. The engines run either direction so to reverse it is stopped at started running the other way. If you are around an old ferry or tug when it is changing directions and you hear a whoosing of air just as the engine starts that is what is going on.

Wouldn't work in a railroad application as the water around the prop acts a fluid coupling/clutch which would have to be another component in a loco. Diesel-hydraulic anyone?

[Randy Stahl]

MK was cutting 20 cyl engines down to 16... I seem to recall the SP running a bunch of them.
Randy

[oltmannd]

QUOTE: Originally posted by Randy Stahl

MK was cutting 20 cyl engines down to 16... I seem to recall the SP running a bunch of them.
Randy

I was always under the impression that the conversion included replacing the 20-645E3 with a 16-645E3. You might be able to salvage the 20 cyl crankcase by burning the end sheets off, cutting the last cylinder off each end, then putting new ends sheets on and machining, but that would be a ton of work. If you did this, you'd need a new 16 cyliinder crank, too, so might as well just get a whole new crankcase while you're at it.

I don't think you could use the old 20 cylinder crank and crankcase and just blank off two sets of cylinders because the throws are set at even increments for 10 sets of cylinders not 8. You'd have big holes in the timing between cylinders firing - I'd be scared of harmonic vibration in the crankshaft - it's bad enough on the 12s and 20s since they're odd fire engines to begin with.

[Anonymous]

I've said it before in another thread, but, EMD cranks, and cams are modular in six and eight cylinder lengths. A twenty cyl. crank is two six's and an eight, a sixteen is two eights. The two eights must be assembled to a different phase angle than the eight to either of the six's to achieve the proper firing order.

[oltmannd]

Thanks, guys. ...learn something new every day, and I've been at this a while.....

[Overmod]

Ditto with oltmannd. This started getting really interesting a bit earlier, when jruppert originally discussed the dynamic-balancing characteristics of 20cyl vs 16-cyl 2-strokes.

I never had firsthand knowledge of 20-to-16 conversion methods; have only seen anecdotal and Web discussions (including that material for ship-engine conversions; there are oil-field engines that are 'converted V-8s' (Ford 460 being a common block) in which four cylinders are powered and four are converted to air compressors or pumps. Discussion of design and balance of these things would be fascinating... but it would be a stretch to consider that to be 'on-topic' for a railroad thread ;-D

I did understand 'blocking off' cylinders to consist of removing power packs for the 'holes' involved, and plating off the crankcase to maintain scavenge pressure, capping or bridging lube lines, etc. etc. etc. It would be my suspicion that 'derating' a 20-cylinder engine would be least cost-intensive if the original crankcase, crank, etc. could be preserved intact, and this would to me imply that the four cylinders taken out of 'service' would NOT be four in a group at one end of the engine if the thing were to be (1) kept in dynamic balance (static balance being done with ringweights on the disconnected crank throws), (2) done to minimize torsion peaks in the crank due to firing order vs. peak compression effort, and (3) built so that its 'new' critical-speed or resonant-vibration characteristics were either known or equivalent/better to existing 645 practice.

Be interesting to see jruppert's detailed analysis of the forces involved in a 20 vs. derated-16 engine with different cylinders out but using the same crank. (Might also be interesting to see whether one or more of the 'removed' cylinders could be changed over to air compression and perhaps improve the dynamic characteristics, without decreasing fuel efficiency (etc.).

My own suspicion btw. is that converting 'extraneous' engine cylinders to air compression, on a locomotive which by law has to have a certain enablement for brake air, is in the same category as 'thermodynamic' enhancements to traditional steam locomotives -- they might work in theory, perhaps even promise Big Money Savings, but by the time you plumb them up, provide redundant safety valves, relief lines, dryers, traps, etc. the overall cost might not be worth it. I can just see some fresh-out-of-college engineers saying 'we can draw the compressor intake air from the filtered intake manifold!' without wondering what this might imply on an EMD 2-stroke...

[broncoman]

in notch 8, how much manifold pressure is being produced a turbo on a 16-645. Does a supercharger, produce as much as a turbo or is it just there for the scavange effect. On the smaller detroit motors that have both turbo and superchargers there is an option to go with a bigger supercharger in-lieu-of having a turbo, so horsepower loss isn't as much as it could be by removing the turbo. The five year turbo life seems to be a constant even on the smaller ones also.

[Anonymous]

Supercharger is not the right term for the blower on a Detroit Diesel, blower is the correct word, because the blower is geared to turn about one and a half times crnkshaft speed to provide a small amount of pressure for exhaust scavenging.

Supercharging weather by turbo or blower is when at the end of intake stroke, the cylinder air pressure is higher than atmospheric. A blower used in the capacity of supercharging can then be called a supercharger. I did not know that Detroits could use a larger blower as an option for supercharging.

In my own experience, I have seen 12v71's are in fact two 6v71's bolted together. 71 blocks and all Detroit blocks are machined with flush ends to which an adapter plate is bolted for accessories, etc.. This allowes an engine to be built in many diferent configurations, the "front" could be on either end of the block, regardless of direction of rotation, fuel pump, heat exchanger, and any other accessories can be mounted in a variety of places. Detroit is not the only manufacturer to do this. EMD blocks have a similar appearence, but the end plates are welded, and the block is a complete block for however many cylinders the engine has.

That said, there is no reason that I can see why a 20 cylinder block cannot be cut to any number of cylinders, because of its construction is of separate peices welded together, instead of a solid casting. Oil and coolant passages are also less of a problem, the block is "dry" with coolant jackets integral to the cylinder liners, and flowing directly to each cylinder head bolted directly to each liner. Coolant flowes from cylinder to cylinder via jumpers. If a block were to be cut, I imagine great care must be taken to maintain proper alignments.

The reason I know that EMD crankshafts and camshafts are modular, is because I used to have an EMD manual for 645 marine engines, it was quite a while ago though, about ten years ago, before my kidneys failed. I was borrowing it from a freind, but it got stolen from my truck because I was living in a bad neighborhood. If I remember, there was a chart showing the bolt pattern of the crank's and cam's ends and the correct holes to align when assembling a crankshaft or camshaft. If for some reason a journal was damaged beyond repair, the whole crank or cam does not need to be replaced, also, if an engine was to be decommissioned and the parts were still usable, they could be assembled in a different engine, but I don't remember any direct reference to modifying the number of cylinders in an engine.

That said, to me, it makes no sense to blank cylinders without changing the firing order, and assembling a shorter crank and cam means the block has to be cut.

I have read that EMD thought long and hard before deciding to build a 20 cylinder engine, because they knew it would break crankshafts. What promted them to explore was IIRC, a Japanese company had succesfully built a 20 cyl. marine engine, that proved to be reliable. About ten years ago Detroit built two 20 cyl. 71 engines as an experiment for an offshore cigarette boat, which was successfull. A twenty cylinder engine has an awfully long crankshaft, and the windup must be terrible, allowing tortional vibration to amplify. If it was hard enough to build one in the first place, why mess with it?

I know enough to know what I don't know, and developing a mathematical model of all the forces and vibrations in a crankshaft is WAY beyond my knowledge or experience. I once copied the equations describing a piston's motion relative to a crank's radius, and a given rod length - "rod ratio", it's three pages of trigonometry and calculus! And that's just figuring the motion let alone the forces or the vibrations. I know enough that I can look at it and point out the major parts and the general meanings, I suppose if I had to, I could take the time to learn more, but if you have ever took the first step of trying to design something, even if you know the equations, that doesn't tell you where to start !!! When all you have is variables and no constants, maybe you understand the relationship between the variables, but that doesn't help you !!!

Anyway, if you can see from the getgo that blanking cylinders is asking for trouble, a complicated mathamatical study is probably not a good idea either !!

[Anonymous]

I would think that a real world example (that we non-locomotive-owning folks could do) of cylinder blocking would be to take a V8, choose two cylinders opposite in firing order and remove the spark plugs. Now start it.
While the V8 is a four-cycle and the engines discussed in the thread are two-cycle, I would imagine the effect would be similar. Also, if one were to install a crank from a V6 (never mind the mechanics- it's been machined to fit) one could run the engine with two cylinders unused with degraded performance but not shaking itself to pieces.

I would think you would almost be required to change the crank.

[Anonymous]

Assuming the v6 and the v8 have the same v angle, stroke and journal dimensions, the block would have to be shortened anyway because the crank needs to drive accessories, oil pump, cams, etc.. Which was my point: if you are going to correct the firing order (build a shorter crank), then you also have to cut the block.

[Anonymous]

Actually blanking a cylinder in a four stroke engine should have a very different effect than in a two stroke engine.

For one, power strokes in a four stroke engine are divided into 720 degrees, while a two stroke's are divided only into 360 degrees.

comparing pistons, con rods, cranks between two and four strokes of comparable output, the four stroke's are always far heavier. In a two stroke engine, mean effective pressures are lower, and the piston is always subject to positive cylinder pressure; this allows two stroke engine components to be much lighter. This is probably why I see so many comments on how EMD's load so much quicker.

The part about mean effective pressure is also one reason two strokes don't make twice the power of a four stroke, another could be pumping losses, because two strokes move about twice as much air.

Anyway, all of these things probably point to blanking cylinders of a two stroke having LESS effect than in a four stroke engine. If a two stroke engine lost a cylinder for any reason, it would probably run smoother than a comparable four stroke losing a cylinder.

The thing is that would be an emergency situation and not the expected running condition of the engine. What would be the long term effect of running an engine with an imbalanced firing order?

[Overmod]

I suspect that the 'long term' effects while substantial may be easy to document. My understanding is that EMD engines with bad power packs are fairly common in service, and often the engine isn't pulled for service until a certain number of them are dead. (Whether or not the engine is pulled immediately for something that isn't an individual-cylinder failure is another matter).

Randy, is there any 'preferential' location for powerpacks to go bad? If not, there can't be any good prediction of what the torsional stress in the crank would be, or what the long-term implications of peak stress might entail. It's been my suspicion for some time that dead cylinders were a major contributing factor to some of the crank breakage on the 20-cylinder engines.

Other reasons why two-strokes don't make 'twice the power' of a four-stroke: a scavenged engine doesn't have the charge density of a four-stroke with intake valves in the conventional position, given equivalent levels of boost. I can't find the reference to 'bmep', but the effective cylinder pressure on a two-stroke might as well be no higher than boost pressure by the time in the stroke that the scavenge ports begin to be exposed, or you'll start to get gas cutting on the rings, one of the places you'd least want it.

Oh, by the way, there are a couple of 24V71s on sale if you want 'em. TA's, too!

http://mdeltd.com/product.php?product=Marine%20Engines

(Scroll down the page a ways to find them)

Nifty looking things; they don't look to me as if they use a pair of 12V71 cranks bolted together, either... There are apparently quite a few yachts that have these things. One wonders, though, how many hours you'd get if you got 1800hp @ 2300 rpm out of them for any length of time <8-O

[oltmannd]

The 3-5 psi for a roots blower engine sounds right, but for a turbo it sounds low. Looking at some test data from 1986 turbocharger/fuel efficiency tests on an SD40-2 at Conrail's test lab in Juniata, we measured about 18 psi.

[Randy Stahl]

18 psi is about right... you can see and hear when the covers are on loose , especiallt in throttle 8
Randy

[Anonymous]

Overmod, very cool. It looks like three eights put together. the exhaust manifold looks homade! 1800 hp from three eights would be 600 hp from each eight, which sounds about right for a marine application 8V71. The only problem I see is the crank is very long. They run to 2300 rpm, but I remember some owners saying they're much happier at 2100 (detroits).

Oh, as far as cylinder pressure being above boost pressure when the scavenging ports are uncovered, doesn't sound right, because the exhaust ports should already be open when the ports are uncovered. Two stroke engines open their exhaust valves slightly early while there is still pressure in the cylinder, the resaulting "pop" gives momentum to exhausting gasses as the ports are uncovered.

[Overmod]

About the scavenge ports/exhaust ports: granted, but my point concerned the effective limit of the piston excursion under power. There can't be any 'blowback' from the piston through the transfer ports to the crankcase under any circumstances. If the exhaust valves open 'early' (as you rightly note they do) it still further reduces the effective duration of the power pulse.

How much earlier do the valves have to be set to give the 'momentum' you mention on an EMD turbo engine over a range of engine speeds? Seems to me you'd have to do this as a compromise, because the back pressure would range substantially depending on the degree of actual boost once the turbocharger turbine took up its proportion of the load (from the mechanical drive) -- which leads to another tech question: what IS the measured back pressure at different loads/speeds on a turbo 645 or 710?

[Anonymous]

The Detroit 71 series manual has a section with an illustration showing a vacuum test of the piston pin bore to ensure air tightness. In my experience as a technician, this is archaic, because nobody assembles power packs anymore, only preassembled power packs are installed, but it does show that it is important to stop communication between the skavenging ports and the crankcase.

As a technician, I have never heard of backpressure having to be measured, but it is probably of concern to an engineer. I imagine backpressure after the turbo is more important for everyday consideration. For an engineer, it would be usefull to compare exhaust backpressure before the turbo to boost pressure on the cold side to determine a turbo's efficiency. Backpressure may be higher because of a turbo, but so is intake pressure and combustion pressure, so really the question is, "Does the relative differences in pressures change?", and this is probably a reflection of a turbo's efficiency.

[Anonymous]

How does exhaust timing differ between turbo and non-turbo engines? you could probably compare exhaust timing at the camshaft between two engines of the same model, but this wouldn't tell you how that difference was determined. That's a question for engineers in a laboratory.

Cutting short the power stroke is a compromise, but poor skavenging also cuts power.

[Randy Stahl]

QUOTE: Originally posted by Overmod

I suspect that the 'long term' effects while substantial may be easy to document. My understanding is that EMD engines with bad power packs are fairly common in service, and often the engine isn't pulled for service until a certain number of them are dead. (Whether or not the engine is pulled immediately for something that isn't an individual-cylinder failure is another matter).

Randy, is there any 'preferential' location for powerpacks to go bad? If not, there can't be any good prediction of what the torsional stress in the crank would be, or what the long-term implications of peak stress might entail. It's been my suspicion for some time that dead cylinders were a major contributing factor to some of the crank breakage on the 20-cylinder engines.

Other reasons why two-strokes don't make 'twice the power' of a four-stroke: a scavenged engine doesn't have the charge density of a four-stroke with intake valves in the conventional position, given equivalent levels of boost. I can't find the reference to 'bmep', but the effective cylinder pressure on a two-stroke might as well be no higher than boost pressure by the time in the stroke that the scavenge ports begin to be exposed, or you'll start to get gas cutting on the rings, one of the places you'd least want it.

Oh, by the way, there are a couple of 24V71s on sale if you want 'em. TA's, too!

http://mdeltd.com/product.php?product=Marine%20Engines

(Scroll down the page a ways to find them)

Nifty looking things; they don't look to me as if they use a pair of 12V71 cranks bolted together, either... There are apparently quite a few yachts that have these things. One wonders, though, how many hours you'd get if you got 1800hp @ 2300 rpm out of them for any length of time <8-O

Usually a dead power pack means that the cylinder has lost compression, hole in a piston , dropped valve , broken rings , broken test ****. All of which would cause excessive crankcase pressure tripping the engine protector OR causing a crankcase explosion. Every 6 months a compression test / airbox inspection is done and the weak ones are changed. 99% of the broken crankshafts Iv'e seen are right where you expect them... at the flywheel end.
Randy