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Old 22nd February 2009, 10:22   #61
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@ vivekiny2k:

First off, thank you. I appreciate your counterpoints and they are truly improving this conversation.

I believe that running the engine at excessively low RPMS is both inefficient and potentially detrimental. Excessive lugging can lead to high cylinder pressures, leading to detonation and even piston slap in extreme cases. HERE is some evidence from "the experts" to support this.

I did not mention anything about efficiency (or lack of it) because this method of driving could potentially harm the engine. I thought I would stop there in my previous post.

I have anecdotal evidence that shows that it is also inefficient. Here is a scenario:

My current speed is 60mph. My target speed is 80mph.

Cruising efficiency (observed numbers):
6th gear: 38 MPG.
5th gear: 28 MPG.
5th gear (80mph): 26 MPG.
However when I accelerate:
In 6th my mileage drops to 18 MPG.
In 5th my mileage drops to 11 MPG.

However the story is that in 6th gear it takes me ~8 seconds to get 80 MPH, but in 5th it barely takes me only 3 due to being in the powerband. @60mph I'm at 1350 RPM in 6th and at 1800 in 5th.

Average MPG rating for the time spent accelerating:
6th: 18mpg for 8 seconds for an average of 18mpg average.
Fuel used in 5th: 11 for 3 seconds and 26 for 5 seconds = 20.3 average.

The point here is that I'm getting better mileage while using a shorter gear. This clearly indicates that something is wroth with using 6th. Even though the engine is turning slower, it is producing lower power per unit volume of fuel consumed in 6th than in 5th. There is no question in my mind that downshifting to 5th is the only solutions.

The more you lug the engine (lower rpms), the wider this efficiency difference in gears. At 1100rpm in 6th, the engine consumption increases under acceleration to 15MPG even though the car isn't even acceleration - what a waste!
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Old 22nd February 2009, 13:52   #62
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Quote:
Originally Posted by vivekiny2k View Post
@anupmathur, true.

all of us load our engines to different levels and types. Some of it may fall into overload if such a boundary is defined somewhere.

EDIT: could you give me a source to support the following
Vikram, what I have basically done is give a 'name' to the phenomenon of an engine being operated at an operating point which is not optimal/healthy.
It is not only exceeding the max power output that represents an overload for an engine; even an engine running below rated output can be 'overloaded' and this is usually a case of temperatures in the engine being higher than optimal for that output, even though the max permissible values have not been breached.
This is often referred to as 'thermal overload' and is detrimental to the life of the engine.

There is always a relationship between the current power generated and the corresponding exhaust temperatures for an engine. The range is defined, although not made available as 'graphs' to a user. Instead users are told to be in a certain gear at certain speeds. Ideally, they should be told what rpm to be at for a the bhp being produced.


What Atlblkz06 has posted, and the link therein, are basically pointing to the same phenomenon.

Thermal overload operation stands rather well defined for marine engines which are often with a fixed propeller and operating at a set or demanded rpm, because that rpm decides the speed of the vessel.

If the rpm is set low and the load is large (due to prevailing, adverse weather conditions, for example) the exhaust temperatures, although well below maximum allowable, are higher than they ought to be for that load/output. (Curves/graphs for safe operating ranges are supplied by makers and these HAVE to be adhered to, so that warranties stay valid)! That is a case of the engine being thermally overloaded. Continuous operation in such a condition is prohibited.

A car is much 'luckier' because it has a gearbox and the operating point for the engine can be shifted in a jiffy, without affecting the speed that is desired. However, if a user insists on 'lugging' the engine, it creates much the same situation for the engine: that it is being operated in a 'barred' zone.

There is no readily available 'source' that will deal with this subject, as it is restricted to the manuals and bulletins for advanced instructions to operating personnel. Perhaps Google can help?
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Old 22nd February 2009, 14:06   #63
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Quote:
vivekiny2k : But those who have lugged the engines also have not had failed engines either. but most of the people are totally bent on making us belive that we will have failed engines. give me some examples. all of us own machiines and operate them based on our experience and intuition.
failing is relative. An alternate explanation could be faster wear-out.

Those who have lugged their engines may not have a "failed" engine as in an engine that's blown-up, broken-down or such. The failure can manifest in it's performance : having to over-haul / rebuild the engine earlier, or things like replacing the clutch faster.

Even people who lug their engines will not push their engines till it no longer runs, before they get it rectified. Not lugging also helps extending the life of the engine in no small measure, and all the while allowing you to enjoy that power-band.

The other part of the ill-effects of lugging have been explained quite well by Atlblkz06 in his last post, summarized & highlighted by this point :
Quote:
Atlblkz06 : The more you lug the engine (lower rpms), the wider this efficiency difference in gears.
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Old 22nd February 2009, 15:23   #64
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Quote:
Originally Posted by vivekiny2k View Post
But those who have lugged the engines also have not had failed engines either.
I know of many who don't change their regular engine oil for 25,000 kms, and their cars haven't broken down either. Should we start following that practice?

Look, we are a team of automotive enthusiasts to whom, the cars we own matter deeply to our lives. We aren't ready to take chances and will do everything we can to keep them in the pink of health. I see engine lugging as little else than abusing the engine!

Last edited by GTO : 22nd February 2009 at 15:27.
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Old 22nd February 2009, 15:54   #65
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Quote:
Originally Posted by GTO View Post
I know of many who don't change their regular engine oil for 25,000 kms, and their cars haven't broken down either. Should we start following that practice?
I can't believe that.

After some time, as spects, shoes, watch become part of body, car also become part of body. Other than car, everything can be changed with comparatively little cost.

Any malpractice affecting car's health should be avoided.
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Old 22nd February 2009, 16:06   #66
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On a recent trip to Pune, my cousin's Wagon R gave only 13kmpl!!!

When i drive our Wagon R i get around 17-18kmpl.

Main difference being that while i keep shifting to the appropiate gears when required and always maintain 25-30% throttle. He keeps the car in 5th for as long as possible (even when the vehicle speed is low) while using 100% throttle to gain momentum.

So always choose a gear that lets you accelerate with minmal throttle. More than the rpm, its your throttle pressure that consumes fuel.

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Old 22nd February 2009, 16:36   #67
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Sorry, folks, but I'm getting a little confused here, and am quoting some of the issues which are not clear to me...
Quote:
Originally Posted by vivekiny2k View Post
... automatic nissan quest, the V6 runs below 2K when cruising at 65 mph on highway on overdrive.
Can you lug an automatic transmission?
Quote:
Originally Posted by rippergeo View Post
I wonder if I lug my engine. I can leave it in third or even 4th at idle and crawl around in the city without jerking/shuddering/knocking, and the car picks up faster than most other vehicles on the road when the accelerator is depressed from that rpm.

theoretically, that increases the load on the mechanical components right?
but, considering that it accelerates with ease from idle in 3rd, it it really lugging?

Driving above 1700rpm in 2nd or 3rd in the city traffic is slightly difficult, because the car will be considerably faster than the surrounding traffic.
You can forget about 4th
Is lugging about driving at a particular gear-rpm combination where the engine knocks/rattles? or is it about driving "below the rev band" where it refuses to accelerates when you ask it to?

Quote:
Originally Posted by Shan2nu View Post
Driving for FE is not that easy.
Its a fine balance between engine speed and vehicle speed.
Is "driving for FE" different from driving at optimum rpm at the highest gear possible? I thought the ideal "drive for FE" would be to sit on the highway on top gear at the rpm where the rpm and torque curves intersect...

Quote:
Originally Posted by anupmathur View Post
In fact lugging will never give the best fuel efficiency, but it might give the best fuel economy!
What's the difference between fuel efficiency and fuel economy?

Quote:
Originally Posted by Spitfire View Post
Lugging what lugging? I drive a diesel
Isn't driving a diesel at 800 rpm on 5th gear lugging?
Quote:
Originally Posted by anupmathur View Post
Efficient operating point and longevity of an engine go hand in hand.

An engine that is being lugged is running in an 'unhealthy condition' known as 'thermal overload'!
You mean an engine being lugged will overheat?

Quote:
Originally Posted by Shan2nu View Post
More than the rpm, its your throttle pressure that consumes fuel.
That's what I thought. I was always taught to "back off" from pressing the throttle every few seconds while maintaining a steady cruise speed (whatever the speed may be) - that improves FE. Is what I do called "lugging"?

From the article Two Ways to Improve Your Mileage: Lug and Coast - Column/Csaba Csere - The Steering Column/C/D Staff/Columns/Features/Car and Driver - Car And Driver quoted elsewhere in this thread, "lugging" and "coasting" seems to be done as a combination, as part of a typically American practice called "hypermiling", as opposed to "redlining". Our long-range cab drivers do "hypermiling" instinctively, while our call-centre drivers "redline" equally effortlessly. So what's new?
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Old 22nd February 2009, 17:08   #68
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Quote:
Is "driving for FE" different from driving at optimum rpm at the highest gear possible? I thought the ideal "drive for FE" would be to sit on the highway on top gear at the rpm where the rpm and torque curves intersect...
Rpm and torque curves intersect? Didn't get that....

What i was trying to say is that "kmpl" depends on a combination of "liters per hour" and "kmph".

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Old 22nd February 2009, 17:18   #69
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Quote:
Rpm and torque curves intersect? Didn't get that....
What i was trying to say is that "kmpl" depends on a combination of "liters per hour" and "kmph".
http://www.team-bhp.com/forum/attach...ower_graph.jpg

As per the above diagram, the rpm where the 2 lines intersect. That's the point of best L/hr...
Agreed. actual km/l depends on a combination of L/hr + km/h. The optimum L/hr usually produces the best km/l if the km/h is automatically allowed to be found by the car's top gear.
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Old 22nd February 2009, 17:27   #70
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Quote:
Originally Posted by SS-Traveller View Post
What's the difference between fuel efficiency and fuel economy?
SS, you've got the answer already in your post:

Quote:
Originally Posted by SS-Traveller View Post
"lugging" and "coasting" seems to be done as a combination, as part of a typically American practice called
Our long-range cab drivers do "hypermiling" instinctively,
Efficient operation requires a certain amount of fuel. In less fuel than that a specific trip can get done by techniques such as lugging and coasting. I'm referring to that as economy.

Quote:
Originally Posted by SS-Traveller View Post
You mean an engine being lugged will overheat?
Need not be in the classic sense.
Kindly read my post # 62 above. I've explained this point.
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Old 22nd February 2009, 17:30   #71
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Quote:
As per the above diagram, the rpm where the 2 lines intersect. That's the point of best L/hr...
You can't really go by one graph alone. Power and torque are represented by many diff units.

This particular graph is represented by kw and nm.

If i were to use bhp and lbft instead, the curves would meet at 5252rpm and if i were to use ps and kgm, the curves wouldn't intersect at all.

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Old 22nd February 2009, 22:30   #72
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Quote:
Originally Posted by SS-Traveller View Post
Can you lug an automatic transmission?
no i don't. however, I try to keep my revs low once cruising, by anticipating stops and not needing subsequent hard acceleration, and not using cruise control except short stretches on flats. takes some discipline. somewhere on this forum there is a pic of my economy meter showing 28 mpg on my quest after a 400 mile drive. real world reported is 22-25. some can term driving at 1700 rpm at 65 mph as lugging.

I did use my engines at low RPMs when i was in india mostly on two wheelers. was a little methodical with the car since i had not driven for more than 6 months when i left.

Quote:
Originally Posted by Atlblkz06 View Post
Cruising efficiency (observed numbers):
6th gear: 38 MPG.
5th gear: 28 MPG.
I think I was referring to using low RPM in this situation. I remember downshifting when going uphill or needing extra acceleration. but still retained low RPM as far as possible.

and I already have explained getting high fuel economy with my driving. and let me reiterate. the avg rpm was low, but the lowest was never in uncomfortably jerky range.

@GTO, I agree with your taking precaution point. I just happen to be bent on fuel economy at the cost of abusing my engine a little. and what i was saying that i did not have any issues for the 30K kms I rode my bike for.

EDIT: yes, I do lugging AND coasting. much easier to do with manual transmission though.
Quote:
Vikram, what I have basically done is give a 'name' to the phenomenon of an engine being operated at an operating point which is not optimal/healthy.
no issues. i was just curious to know how i was affecting my engines.and the name is Vivek

Last edited by vivekiny2k : 22nd February 2009 at 22:46.
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Old 22nd February 2009, 23:51   #73
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I am very much afraid of lugging also not interested in giving clutch in third and second gears to help the car pull away.
so more often I uses first gear usually in bumper to bumper traffic and wen there s a hump.
I have noticed sometimes wen car is in motion(but in very low RPM s) and I try to put 1st it is hesitant to engage.

Am i doing any thing wrong??
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Old 23rd February 2009, 00:19   #74
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Wait a second. Where did you get the idea that peak torque = peak efficiency? If that was the case, then all engines would run at a constant 5252 RPM and all the transmissions would be CVTs.

The most efficient engine RPM depends entirely on the load applied. If the load is so great that the engine has to work at above the torque peak, then a bigger engine is needed. Low load = low RPM requirement. However this only applies to a certain limit. when you drive below this limit - the engine is struggling and the "less rpm = less fuel used" argument no longer holds true under load.

Look at it this way - with each gear selected, its like having a new "equivalent engine" with its own set of torque and efficiency curves. As speed increases, the load increases dramatically (aero). This is why at high speeds you have to rev the motor past its torque peak to get the maximum HP.

I came up with a little graph to sort of put in pictures what I've noticed.

Let me know what you guys think:
Attached Images
File Type: bmp speedchart.bmp (916.2 KB, 1592 views)

Last edited by Atlblkz06 : 23rd February 2009 at 00:25.
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Old 23rd February 2009, 09:36   #75
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Quote:
Originally Posted by Atlblkz06 View Post
I came up with a little graph to sort of put in pictures what I've noticed.
Excellent compilation, Atlblkz06!

This would certainly help clear up some of the issues that came up earlier in the thread.
I'm listing some of them below:

Quote:
Originally Posted by watashi75 View Post
My understanding is that fuel efficiency leads to fuel economy.
Quote:
Originally Posted by SS-Traveller View Post
What's the difference between fuel efficiency and fuel economy?
Quote:
Originally Posted by anupmathur View Post
Efficient operation requires a certain amount of fuel. In less fuel than that a specific trip can get done by techniques such as lugging and coasting. I'm
New debates can start and views expressed now!

Last edited by anupmathur : 23rd February 2009 at 09:37.
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