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Author Topic: On lugging a Detroit Diesel  (Read 4781 times)
coolbus
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« on: June 27, 2007, 08:22:50 PM »


On lugging a Detroit Diesel...

I am aware that lugging a Detroit is a no no, but I read in another post that lugging is defined as 'any time you are asking the bus to accelerate, but are not able to, or are actually losing speed' (paraphrased).

I always thought that lugging only occured when the engine RPM dropped below a certain point.

I probably lugged my 8v-71 quite a few times on my 2500 mile trip accross the US. (based on the info in the article)  The engine never did overheat - in fact, the temp guage barely even fluctuated when pulling the several long grades I came accross along the interstate. And I always watched for black smoke - none produced.

Is the only danger in lugging a Detroit an overheat situation?

thanks
Mark
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« Reply #1 on: June 27, 2007, 09:26:22 PM »

Hi Mark, that description sure takes up alot of space! I agree with your statement on lugging being below a certain point. If an engine is hot, my preference has always been to keep the water pump turning max rpm. I always thought black smoke was good if it was mine!
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« Reply #2 on: June 28, 2007, 03:53:24 PM »

Luggin is when you are asking your engine to pull a gear that it can't.  simply, if the bus won't accelerate in that gear it is to high a gear.

this is generally associated with lower RPM ranges.  If you are at the governor chances are you are not lugging.

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gus
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« Reply #3 on: June 28, 2007, 07:42:05 PM »

Lugging is overloading the engine no matter what the rpm, it means that the engine is not generating enough power for the situation.

If you runout of gears and still can't move the bus the ultimate lugging is stalling.

Normally, in a bus, it means that you are trying to pull a hill without shifting down to the next lower gear when, as said before, the bus will no longer accelerate and usually will be losing speed no matter how far you push in the fuel control.

Black smoke results because the engine is being fed more fuel than it can burn.

All this is my personal understanding and subject to correction by the experts!!
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« Reply #4 on: June 28, 2007, 08:06:23 PM »

Luggin is when you are asking your engine to pull a gear that it can't.  simply, if the bus won't accelerate in that gear it is to high a gear.

this is generally associated with lower RPM ranges.  If you are at the governor chances are you are not lugging.


My opinion is that you could be at the governor and still be lugging the engine.

I do not think you should ever have the pedal to the metal. You should back off the pedal a little bit so that if you increase the pressure the engine speeds up. If it will not speed up then you are lugging the engine and should shift to a lower gear.
Richard
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« Reply #5 on: June 28, 2007, 09:05:27 PM »

I don't think you can overload/lug at max RPM or at the top end of the RPM range.

if your load is great enough that the sequence starts to where you will be lugging your RPM will be dropping.

keeping the bus in the higher gear at a lower speed, while providing max fuel flow is lugging

if your at MAx RPM your using max fuel, or close to it.

unless of course your going downhill and your bus has reached the max speed it can do with the given wind resistance and your still holding the throttle at max.

my 04 going down the Westbound grade into Vail would max out at 76mph....no throttle or full throttle, I suppose if I gave it full throttle in that situation it would be lugging

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buswarrior
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« Reply #6 on: June 28, 2007, 09:53:21 PM »

Check the torque curves of the detroit 2 strokes.

Won't stay at top RPM (against the governor) under a gross load, not enough torque up there.

Be happy, if it makes full RPM's, you aren't loading it enough to create a lugging condition.

The concept missing in all this is to match the throttle position to the work the engine is doing, and no more. The engine will reach that point during the climb, that it won't accelerate, but it is maintaining speed at an acceptable RPM. That is not lugging. The throttle pedal should be eased back to match that point, not be held mashed to the floor. A pyrometer in the exhaust is a great gauge for showing the results of getting it right or wrong.

Otherwise, I like what I've read here.

happy coaching!
buswarrior
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« Reply #7 on: June 29, 2007, 12:15:22 AM »

Lugging a diesel engine is more of a concern with the low rpm/low oil pressure problem associated with older design engines. When the manufacturers came out with constant displacement oil delivery systems in 4 stroke engines ( I know next to nothing about 2 stoke engines) they quit worrying about lugging. I'm thinking if your oil pressure is acceptable you are not abusing the engine at any reasonable rpm at full throttle. I've owned trucks which operated at full throttle at 1300 rpm for hundreds of thousands  of miles between overhauls. That same block with the old style lube system would have lived a short life at that rpm.
« Last Edit: June 29, 2007, 12:16:56 AM by gecole » Logged
RJ
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« Reply #8 on: June 29, 2007, 12:33:16 AM »


 ( I know next to nothing about 2 stoke engines)


Thanks for qualifying your remarks with the above statement.

Two-strokes are different than four-strokes, and what works for a four doesn't necessarily work for a two, and vice-versa.

"I'm from the government - I'm here to help" killed the OTR two-stroke, not the engine's design.

Not too many engines originating in the 1930s survived as long as the two-stroke Detroit. . .

As good as the Series-60 is, it's future is dim, again, thanks to government intervention trying to save us from ourselves.

FWIW & HTH. . .

 Wink
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« Reply #9 on: June 29, 2007, 06:33:08 AM »

The original way that the 2 strokers were tuned (71 series using 60 injectors, 92 series using 80 injectors) were aimed at the fact that the bus drivers drove the bus more like if they had an on/off switch rather than a variable position gas pedal.  Even increasing the injectors to factory settings (71 series using 65 injectors, 92 series using 90 injectors), the engines were still tuned to be operated for short periods of time (15 minutes per hour) at full throttle without damage to the engine.  Do you think truck drivers back in the 70's with non turbo 8V-71's were babying their engines?  Most owner/operators then increased their injectors to 70's, changed the timing, and many times revved them to 2800rpm with actually good results.  With my past truck with the 8V-92TA mechanical (435hp) I always had my foot in it climbing hills, but watched radiator temp like a hawk (still do) and got an almost unheard of 500,000 miles out of the engine before overhaul. 
If you have a 4 or 5 speed manual-shifting is simple-accelerate up to governor limit then shift.  Simply notice the speed that you up shift at and then downshift back down at the same speed for that gear.  If you have an automatic, you can't lug the engine-but you can overheat the transmission when climbing a steep grade in converter mode (that's a whole different story).
Final thoughts-most of the engines in our buses are under powered making running down the road without your foot on the floor almost impossible.  Drive the bus as described and the engine most likely will out last your usage of the bus.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
belfert
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« Reply #10 on: June 29, 2007, 09:45:49 AM »

As good as the Series-60 is, it's future is dim, again, thanks to government intervention trying to save us from ourselves.

The Series 60 could possibly be modified to meet 2010 emissions standards, but Detroit has choosen to go with just one engine for 2010 and beyond.  They have the MBE 4000 and Series 60 now and the MBE 4000 or a successor will be the only choice starting in 2010.
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« Reply #11 on: June 29, 2007, 10:55:03 AM »

I agree with Tom C. If I didn't have my foot to the floor the whole time, I wouldn't get anywhere. Those 2 stroke engines are underpowered, but they were made tough. They are meant to be used. Down $#!% when it obviously won't stay in a gear without slowing down or heating up. Enjoy the "screamming" from back there. When the engine is done, which will a long time, rebuild it and drive it for another life time. If you want to baby it, do it with proper maintenance.
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JC
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« Reply #12 on: June 29, 2007, 11:10:47 AM »

Belfert, i have been hearing that the 60s were going away for 4 years and they out sell any engine on the market like they out sell the mbe 4000 by 5 to 1 the Germans are not dumb they bought DD just to get the DDEC because they could not make a electronic system to work
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« Reply #13 on: June 29, 2007, 12:19:11 PM »

The Series 60 could possibly be modified to meet 2010 emissions standards, but Detroit has choosen to go with just one engine for 2010 and beyond.  They have the MBE 4000 and Series 60 now and the MBE 4000 or a successor will be the only choice starting in 2010.

Brian MBE 4000 (Mercedes Benz Engine) Detroit Diesel, Setra, etc. = DAIMLER CHYRSLER! HMMM!
FWIW! BK Grin
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Busted Knuckle aka Bryce Gaston
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Buffalo SpaceShip
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« Reply #14 on: June 29, 2007, 01:02:57 PM »

my 04 going down the Westbound grade into Vail would max out at 76mph....no throttle or full throttle, I suppose if I gave it full throttle in that situation it would be lugging

I sure hope you're not behind me (or anyone else) in a twelve ton vehicle coming down a 6% grade in top gear at top speed. Wow!  Shocked Your brakes are not sufficient to stop the coach at that grade/ speed, or even slow it down that much. There is a runaway ramp after the first bend coming down into Vail that might help.  Wink

BTW, a 8 to 10% downgrade on my old '06 was enough to overwhelm the governor and overspeed the engine, requiring me to use the brakes to moderate... but that was in first or second gear, not fourth. I now have Jakes on the '08 and swear by 'em for mountain driving.

The old adage, "go down the grade in the gear you climbed up it" is golden. Even with Jakes.

Brian B.
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Brian Brown
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« Reply #15 on: June 29, 2007, 01:15:36 PM »


my 04 going down the Westbound grade into Vail would max out at 76mph....no throttle or full throttle, I suppose if I gave it full throttle in that situation it would be lugging
Did you have a tachometer?
On any big downgrade my Eagle would continue to increase speed, It never maxed out. The highest rpm I ever got was 2500, but it was still increasing when I turned the Jakes on. Speed was past the peg on the speedometer, but I estimated 85mph.
Richard
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« Reply #16 on: June 29, 2007, 01:23:11 PM »

My B500 allison kicks it up to a higher gear if I exceed 2200 rpm.  kind of scary before I added jakes.

And I confess, I have had it up to 90 or a little better.  I try  not to use the brakes at anything over 70 or 75, they don't really work anyway at the higher speeds.  5 lanes of open road, no traffic.  I hate to think what it did for my fuel mileage.
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« Reply #17 on: June 29, 2007, 02:46:00 PM »

You're lugging when you can no longer maintain speed at a given throttle setting, this includes at governor limit. You are overloading the engine.

DD, like almost any other engine, do not produce max torque at max rpm, all they do at max rpm is go faster. Max torque gives you the most work for your money. In my 671 that is around 1400-1600 rpm, but who wants to go that slow!
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tekebird
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« Reply #18 on: June 29, 2007, 02:54:23 PM »

True, but as the bus loses speed on the grade prior to the downshift it isn't lugging, it is doing what all other engines do while it is being loaded. or do you suggest to put the clutch in until the bus speed is down to the next gears top end then shift.  if this is the case on a grade that would require 2nd gear you should be in 2nd at the bottom because as soon as you start "bleeding" speed your luggin your engine?Huh?

I agree max Torque and max HP are not at Max RPM

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Buffalo SpaceShip
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« Reply #19 on: June 29, 2007, 03:56:03 PM »

True, but as the bus loses speed on the grade prior to the downshift it isn't lugging, it is doing what all other engines do while it is being loaded. or do you suggest to put the clutch in until the bus speed is down to the next gears top end then shift.  if this is the case on a grade that would require 2nd gear you should be in 2nd at the bottom because as soon as you start "bleeding" speed your luggin your engine?Huh?

An engine that can't pull a certain grade at partial throttle will soon lose enough RPM to be lugging, necessitating a downshift. A MUI engine under full fuel is in danger of overheating at any speed/grade. I suspect a DDEC is a different beast, and I have no experience with them. But as buswarrior so aptly states, a pyrometer is the best metric to determine throttle position and gear selection. Otherwise, 1500-1700rpm at partial throttle, with constant vigilance of the temp. gauge and black smoke from the tailpipe, is the safest bet on climbing grades. Automatic trannies are best shifted manually, because they will indeed lug an engine and shift down way too late. A tranny temp gauge is also a wise choice when climbing w/ automatics. Some autos utilize heat exchangers that only dump tranny heat into the engine cooling system, making climbs even harder.

Once I get my 4108 up to over 10,000MSL with my 8v71 and C65's, I'm blowing black and running hot no matter what I do. I attempt to get first lockup on my V730 and climb at partial throttle until the engine hits 200deg, pull over until she cools, and do it again. I suspect rad. misters and/or smaller injectors are in my future upgrade package if I choose to do a lot more high-elevation mountain climbin'. Or a smoke turbo, if I happen to hit the lotto!

FWIW,
Brian B.
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Brian Brown
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« Reply #20 on: June 29, 2007, 06:03:09 PM »

And how do you kook up a pyrometer gauge 40 feet away from the sensor/thermocouple? Does anyone know?
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JC
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« Reply #21 on: June 29, 2007, 06:20:44 PM »

Ah, well I can think of 2 ways! 40' or wire or use a regular guage,sending unit & stc. and use a camera to keep tabs on it! I've heard of several folks who've done just that, built a small box containing a set of gages with a camera in it to acurately monitor their engines performance! I think it's a way cool IDEA. I hope to do the same some day! FWIW BK Grin
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Busted Knuckle aka Bryce Gaston
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Dallas
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« Reply #22 on: June 29, 2007, 06:45:07 PM »

And how do you kook up a pyrometer gauge 40 feet away from the sensor/thermocouple? Does anyone know?


Why not use remote data aquisition?
Nascar and the other major racing associations have been doing it for years.

Here's one from Advantage Motorsports:

EGT (Exhaust Gas Temperature) and/or
CHT (Cylinder Head Temperature)

These Racing Exhaust Gas Temperature sensors are available for those who require to know specific EGT temperatures at ANY portion of the racetrack.  Data graphs are plotted throughout the racetrack to let you see exactly what your engine is doing at any given point. Exhuaust Gas Temperature EGT sensor have exposed tips (not sealed tips) to give the fastest EGT reaction times to measure fuel mixture changes FAST.

  Note: Our temperature probes are designed specifically for high pressure racing appplications and should not be confused with "standard" EGT probes

$60 EGT or Cylinder Head Sensor with 2' Stainless Steel Lead.


http://www.advantagemotorsports.com/Sensors.htm
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belfert
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« Reply #23 on: June 29, 2007, 07:01:54 PM »

Why not use remote data aquisition?
Nascar and the other major racing associations have been doing it for years.

Nascar has an almost unlimited budget for this sort of stuff, some of it paid for by TV so they can overlay the data on the TV broadcast.

Busnuts generally don't have Nascar type budgets.  The price for the sensor is good, but I can't exactly figure out how much the rest of the system would cost.  It looks like $600 and up.

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« Reply #24 on: June 29, 2007, 07:18:29 PM »

teke,

No, the bus has been loaded all the time if it is pulling a hill. It is slowing down precisely because it is overloaded in that gear. It wouldn't lose speed if it weren't overloaded. Once you shift down to the proper lower gear you will be able to maintain a pretty much constant speed even though it will be a lot slower than you would like.

We busnuts are at a distinct disadvantage because we only have four speeds (most of us) and we have to compromise. I wait until the bus is a few mph above the next lower gear max mph and by the time I complete my shift down it is about right. At least that is always my plan!! When it no longer will maintain speed I slowly back off on the throttle until it slows down to this desired speed if it isn't already there. You can tell when more throttle does no good or if really over fueled you can see the black smoke. There is no point in holding the same amount of throttle if the bus is slowing.

If we had a nice 10-15 speed trans we could keep the engine at torque peak or at whatever rpm we wanted, there wouldn't be nearly the speed losses we suffer with only four speeds simply because we would not lose so much momentum between shifts.
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« Reply #25 on: June 29, 2007, 07:24:34 PM »

Here's the good news. You can purchase the Pyrometer of your choice from Isspro. They are the leader in the Pyrometer field for trucks. A nice one is $100 and they have several to choose from. (I prefer adjustable). The other thing you need is a lead from the engine to the dash of your bus. The 40 foot lead is part number R66-40 and sells for $74.54. The 35 foot lead is part number R66-35. Ref, Isspro.com on line catalog.
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« Reply #26 on: June 29, 2007, 07:53:06 PM »

Hey guys, fully loaded isn't lugging and it isn't the same as overloaded.  An engine that is slowing down with wide open throttle (max fuel in a diesel) is fully loaded and not over loaded.  Once it gets to the speed that allows a downshift it's certainly prudent to downshift.  Most automotive engineers define lugging as operation at engine speeds below the torque peak with wide open throttle. The torque peak on an 8V71 with standard timing is at about 1200 RPM, with advanced timing it's 1400 RPM.  My transmission ratios make 2100 in second the same road speed (30 mph) as 1250 in third which is a very good reason no one should put the so called 318 into a GM bus.  Also I've driven my bus over the continental divide 7 times, several times in 95 degree temperatures, without overheating or much black smoke probably because I have N60 injectors and standard timing.  I remember one  stretch of I70, in Wyoming where wide open in 4th gear it took 8 miles to slow from 70 to 60 and it was all over 6000' MSL. 
Regards
Jerry 4107 1120 
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« Reply #27 on: June 29, 2007, 09:39:04 PM »

I've driven my bus over the continental divide 7 times, several times in 95 degree temperatures, without overheating or much black smoke probably because I have N60 injectors and standard timing.  I remember one  stretch of I70, in Wyoming where wide open in 4th gear it took 8 miles to slow from 70 to 60 and it was all over 6000' MSL. 
Regards
Jerry 4107 1120 

Jerry I'm sure you meant I-80/Wyoming or I-70/Colarodo or Utah. I been all over this great land of ours and at no time or place has I-70 ever gone through Wyoming that I am aware of. FWIW BK Grin
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« Reply #28 on: June 29, 2007, 11:21:14 PM »

Common expression of lugging is:
“If you drive too slowly in third gear, you'll lug the engine”


True definition of “engine lugging” is over throttle (added more fuel or decrease Air/Fuel ratio) while engine in max straining order at low RPM at a given torque below the needed vehicle’s torque load to gain speed. Another word need to shift down so vehicle’s loaded torque is below engine’s strong to max torque load. Otherwise unable to increase RPM plus thick black smoke. It very hard on engine’s rod bearing (squeeze oil to a point of touching crankshaft‘s journal while in power down stroke) & piston’s skirt to a point of stuffing.

If you only lugging momentary or 2-3 seconds….it usually ok but do not make a habit of doing it again.

Lugging is expensive…either now or later, period!

FWIW

Sojourn for Christ, Jerry
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« Reply #29 on: June 30, 2007, 05:34:26 AM »

Bk,
 You are absolutely right the long fast climb is on I 80, westbound.  The steepest bit of interstate was on I70 eastbound approaching the Eisenhower tunnel, that was where I had to use second gear. It must be my age showing I was thinking I80 and typed I70.
Regards
Jerry 4107 1120
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