In the vein of the thread asking why idling is so bad, what (technically) is lugging (I understand it is putting high load at low rpms, but beyond that...) and why is it so bad for the engine? How do you know when you are lugging and when you're not?
What is lugging and why is it so bad?
- Thread starter timzak
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Old timers definition of lugging:Increased throttle without increased acceleration.
There has to be a balance between operating in an engines torque curve and road speed.I imagine an engines bearings and maybe its wristpins suffer under lugging conditions.
Probably not $5 worth of fuel saved in a given year lugging vs operating in its powerband.IMHO.
Mark
There has to be a balance between operating in an engines torque curve and road speed.I imagine an engines bearings and maybe its wristpins suffer under lugging conditions.
Probably not $5 worth of fuel saved in a given year lugging vs operating in its powerband.IMHO.
Mark
Yes lugging is a loaded engine at low rpms. The worst case is at WOT and the engine is decellerating.
The problem is the heat created by the burning fuel is not being exausted fast enought and replaced by cool intake air. The hot gasses transmit more heat to the valves heating them up. The end result is that it's hard on the valves.
It's also hard on the bushings and crank because they take a beating. At low rpm the burnt gas expands, but has no place to go.
The problem is the heat created by the burning fuel is not being exausted fast enought and replaced by cool intake air. The hot gasses transmit more heat to the valves heating them up. The end result is that it's hard on the valves.
It's also hard on the bushings and crank because they take a beating. At low rpm the burnt gas expands, but has no place to go.
Also,
Add in that low rpm, high load puts much more loading on crank and rod bearings. Keeping the engine at low rpm may not keep enough oil flowing thru the system to adequately protect the bearings.
From what I have seen using a mechanical gauge on my engine for oil pressure, the oil pressure is not as high as it could be till 2200-2600 rpm. Combine that with high load and it could be trouble.
It stays at about 35psi at idle. This is a blueprinted engine too. Oil pump makes up to 75 psi at full pressure, but full pressure is not reached till 2600 rmp.
Most likely not true of all engines, but I think it demonstrates what I wish to get across.
Dan
Add in that low rpm, high load puts much more loading on crank and rod bearings. Keeping the engine at low rpm may not keep enough oil flowing thru the system to adequately protect the bearings.
From what I have seen using a mechanical gauge on my engine for oil pressure, the oil pressure is not as high as it could be till 2200-2600 rpm. Combine that with high load and it could be trouble.
It stays at about 35psi at idle. This is a blueprinted engine too. Oil pump makes up to 75 psi at full pressure, but full pressure is not reached till 2600 rmp.
Most likely not true of all engines, but I think it demonstrates what I wish to get across.
Dan
On a steep hill, for example.
Maybe I'm wrong but I don't think "lugging" has anything to do with whether or not the car is accelerating. You can be a WOT on a steep hill, with the car decelerating, with the engine spinning at or near its peak torque RPM (usually somewhere between 2500 and 5000 RPM).
In this situation, you've got plenty of oil pressure, the engine is spininng fast enough to avoid excessive bearing wear, and the cam / ignition timing is optimal. In short, you're loading the engine at an RPM at which it was designed to be loaded. No harm done. If the deceleration continues and the RPM drop too low, you should downshift.
To me, "lugging" means you're loading the engine at an RPM lower than what it was designed to take a load. As a general rule, take 1/2 the RPM at which the engine develops its peak torque. You don't want to load the engine heavily or use WOT below that RPM.
Lugging is bad because the engine's ignition timing, valve timing, and bearings are designed for a certain RPM range. If you load it below that range, you are going to get detonation, excessive bearing wear, etc.
Deceleration at WOT may be a quick & easy rule of thumb to know when to downshift, but it doesn't necessarily mean the engine is lugging.
[ December 21, 2003, 02:08 PM: Message edited by: MRC01 ]
So driving at a low rpm (say, 1000 rpm on a V-8 or 1500 rpm on a typical 4-banger) does not necessarily equate to lugging the engine? If the car is still able to accelerate with part-throttle response, no harm done?
Lugging to me means driving a manual tran vehicle in a higher gear than dictated for the engine power band. Like driving in 4th gear at 20 mph up a hill and accelerating to 60 mph without downshifting. Lugging = Running in the wrong gear and forcing the engine to work harder that it needs to if you have selected a lower gear.
I think the idea of going uphill at low rpm in too high of a gear is exactly right. I've read that the load on the bearings increases with the square of the rpm, except that under lugging condidtions the load on the bearings will go right off the chart. I think older carburated vehicles might be more susceptible because of the amount of gas that can be dumped into the intake when you go WOT. Old timers used to throw a rod keeping it in high gear when going up a hill, even when the speed fell off. Something has to give when you do that. Imagine how your knees would feel on a multispeed bike going uphill and you refused to downshift.
John
John
My Dad never downshifted untill the truck literally started to shudder, Now "THAT`S LUGGING"!!!
Hasbeen
Hasbeen
Lugging, yup, the engine shudders and goes "uh, uh, uh, uh, uh". It's actually begging for that down-shift.
[ December 24, 2003, 04:26 PM: Message edited by: Rick in PA ]
[ December 24, 2003, 04:26 PM: Message edited by: Rick in PA ]
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