Lugging -- what's that sound?

[rationull]

Seeing as most of the miles I've driven, by far, have been in stick shift vehicles, and at that I've driven in hilly environments a lot in vehicles that don't have a surplus of low end grunt, I've had my share of accidental lugging moments. I hate that feeling, when I realize I've let the clutch out a little too quickly without giving it quite enough gas, and you get a little shaking and that rattling sound.

So my question is: what exactly is the "rattling" sound you get when you lug an engine for a second? Is it the motor rattling against its mounts, just the sound of the spark explosion hitting the piston in a detonation event, or what?

 

[oilboy123]

I think it's the shock waves rattling the pistons, or some such.


WHAT IS DETONATION?

Detonation (also called "spark knock") is an erratic form of combustion that can cause head gasket failure as well as other engine damage. Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to autoignite. This produces multiple flame fronts within the combustion chamber instead of a single flame kernel. When these multiple flames collide, they do so with explosive force that produces a sudden rise in cylinder pressure accompanied by a sharp metallic pinging or knocking noise. The hammer-like shock waves created by detonation subject the head gasket, piston, rings, spark plug and rod bearings to severe overloading.

Mild or occasional detonation can occur in almost any engine and usually causes no harm. But prolonged or heavy detonation can be very damaging. So if you hear knocking or pinging when accelerating or lugging your engine, you probably have a detonation problem.

 

[tig1]

Ignition ping. Also lugging an engine can cause rod bearing failure over time.

 

[SteveSRT8]

as it relates to modern vehicles there is no such thing as lugging.

Also there will be no abnormal wear or other issues.

Lugging pertains to old pre-computerized vehicles that had poor spark control and actually could be harmed. On any newer model car in proper operating condition this cannot happen.

 

[NateDN10]

Originally Posted By: SteveSRT8
as it relates to modern vehicles there is no such thing as lugging.

Also there will be no abnormal wear or other issues.

Lugging pertains to old pre-computerized vehicles that had poor spark control and actually could be harmed. On any newer model car in proper operating condition this cannot happen.

But what causes the difference in noise? In my car, for example, going above maybe 50% throttle at 1500 RPM in 3rd gear or higher results in a much louder, less smooth, almost diesel-like sound. I'd call that lugging.

 

[IndyIan]

Originally Posted By: NateDN10
Originally Posted By: SteveSRT8
as it relates to modern vehicles there is no such thing as lugging.

Also there will be no abnormal wear or other issues.

Lugging pertains to old pre-computerized vehicles that had poor spark control and actually could be harmed. On any newer model car in proper operating condition this cannot happen.

But what causes the difference in noise? In my car, for example, going above maybe 50% throttle at 1500 RPM in 3rd gear or higher results in a much louder, less smooth, almost diesel-like sound. I'd call that lugging.

Especially with a 4 cyl, with rpms that low, each firing of a piston has time to shake the engine. Also the engine mounts aren't setup to absorb such low frequency vibrations so it rattles the car. Also I think the exhaust and intake sound different perhaps because the cylinder pressures are higher for the power stroke?

 

[Nick R]

It's not hard to do it with the shadow if you keep it in a higher gear and go slower. Hit the gas, and it's not good.

 

[FZ1]

Drivetrain. Just retain the lower gear for a longer period of time,no need to use all of your gearbox from red light to red light.

 

[punisher]

The noise is the sound of detonation occuring due to a combination of throttle opening, engine RPM and load.

Large throttle opening+high engine load+low RPM= a mixture that ignites way too early for a given RPM/piston speed. The increased cylinder pressure at the end of the combustion triggers detonation.

 

[mechtech2]

Originally Posted By: SteveSRT8
as it relates to modern vehicles there is no such thing as lugging.

Also there will be no abnormal wear or other issues.

Lugging pertains to old pre-computerized vehicles that had poor spark control and actually could be harmed. On any newer model car in proper operating condition this cannot happen.


Pretty clear by Steve.

I remember a GM engineer in Car and Driver who lugged a test car, and the editors were horrified. He pointed out "So what?". There is no/low power at lug speeds, so no damage. he did it all the time with no concern.

I believe you are hearing spark knock. A little here and here is of no concern.

And as to multiple flame fronts 'colliding' with damage, that is a disproven myth. What do you think happens in multiple spark plug engines?

 

[dailydriver]

Originally Posted By: mechtech2
Originally Posted By: SteveSRT8
as it relates to modern vehicles there is no such thing as lugging.

Also there will be no abnormal wear or other issues.

Lugging pertains to old pre-computerized vehicles that had poor spark control and actually could be harmed. On any newer model car in proper operating condition this cannot happen.


Pretty clear by Steve.

I remember a GM engineer in Car and Driver who lugged a test car, and the editors were horrified. He pointed out "So what?". There is no/low power at lug speeds, so no damage. he did it all the time with no concern.

I believe you are hearing spark knock. A little here and here is of no concern.

And as to multiple flame fronts 'colliding' with damage, that is a disproven myth. What do you think happens in multiple spark plug engines?



What about the rod bearing damage over time claims, also garbage?? (I'm asking seriously, NOT being snide/sarcastic!)

 

[FZ1]

Common sense. If you can feel your drivetrain struggling,as in lugging,that's not a good thing.

 

[sittingduck57]

At the very least, most engines tend to use more oil when you lug them. I, as "yall", always heard it was really hard on rod bearings.

 

[rationull]

Regardless of what anyone says about modern computer controlled engines, and whether "lugging" exists or is damaging, there is clearly a point when the engine speed is too low, especially in manual trans vehicles if the clutch is let out too quickly, where the engine bogs and sounds awful.

I definitely recognize the difference between newer cars and older ones, having driven carbureted vehicles, early FI vehicles, and brand new ones. I don't get pinging or rough running at low engine speeds when accelerating lightly from a cruise in newer cars, for instance -- I think that can be chalked up to better engine control. But there's still such a thing as asking too much, too quickly, at too low an engine speed.


So, the consensus seems to be that the sound is probably spark knock. It's louder than I would've thought.


EDIT: I really thing the clutch probably has a lot to do with this. Changes in throttle position can be managed by the computer down to the finest details these days, but it seems like rapidly increasing load from engaging the clutch plate to the flywheel would be harder to manage quickly.

 

[ltslimjim]

Doesn't rev-matching help with this, especially on older vehicle with a clutch/MT setup?

 

[Shannow]

Originally Posted By: mechtech2
And as to multiple flame fronts 'colliding' with damage, that is a disproven myth. What do you think happens in multiple spark plug engines?


End gas autoignition involves two opposing flame fronts. One by the spark, and one by the compression ignited end gasses.

It involves damage, but not from colliding fronts.

 

[Shannow]

Lugging in the traditional sense with carbs was approaching a load where engine speed fell markedly with marked throttle opening doing nothing but further reduce speed.

Drastically increased cylinder loading, with a drastically reduced bearing oil wedge due to lower speeds meant bearing contact (pounded bearings).

 

[Spazdog]

I drove a Triumph Spitfire 1500 to Denver once...just once.
Going over a pass that was something like 9000 ft, I thought for certain I was going to kill it. Overdrive off, 3rd gear, wide open throttle it was lugging real bad. (at least there was an 18-wheeler in front of me that was having trouble so the line of cars behind me might not blame the poor mimosa yellow roadster for the slow speed) And the little OHV cast iron Triumph motor only has 3 main bearings so it's not like the bottom end of that engine was anything you would consider durable.
It was cursed with 7.5:1 compression so compression ignition was minimized at least. That may have actually saved me from killing it.

But I did have a lot of knock and ping in my Hyundai SCoupe at low rpm/light throttle. It was apparently a carboned up EGR valve. Cleaning the EGR solved that problem.

 

[Hokiefyd]

Originally Posted By: Shannow
Lugging in the traditional sense with carbs was approaching a load where engine speed fell markedly with marked throttle opening doing nothing but further reduce speed.

Drastically increased cylinder loading, with a drastically reduced bearing oil wedge due to lower speeds meant bearing contact (pounded bearings).


This is how I define "lugging". It's at an RPM that's barely enough to keep the engine running at a reasonable speed for the load (usually 1500 rpm or less) and you get a severe grinding sound with an associated vibration from the engine that feels very much like bearing surfaces making contact with each other.

This is probably the reason (true metal contact) for "it's bad for the engine" when truly lugging an engine.

 

[mechtech2]

I do not say lugging is proper driving technique.

But as to engine wear, I do not believe there is a problem.

BTW, it seems that on modern cars, I can't get a good 'lug' like before [thrump thrump thrump]. Just no power and much smoother than before.