I'm a software guy and I'll be the first to admit that I don't have any experience with ICEs aside from driving and simple maintenance (fluid changes, fuel injector replacement, etc). The downsides to over-revving an engine are pretty clear IMO; higher speed comes with higher ring and bore wear, and if you run your engine way too fast you can get valve float and valve contact w/ the pistons (ignoring rev limiters).
But I've always been cautioned to avoid lugging an engine and that's given be a little bit of irrational fear of running the engine at too low a speed. I've got some understanding of the reasoning behind this but there are lots of holes. In my detail-obsessive post of the week, I'd like to clear some of those up. What are the problems connected with running an engine at too low a speed, and how exactly does the term "lugging" apply?
One clear problem is that there's a point at which the engine is spinning just fast enough to maintain adequate oil pressure. This point must vary based on engine/oil pump design, and to run the engine below that point would cause lubrication problems. It's not clear to me that this point should have too much correlation with displacement, so presumably it would be close to the same whether you're talking about a 6 liter V8 or a 1.5 liter 4 banger. Correct?
Depending on engine displacement and tuning, every engine has a unique torque curve. Thus, depending on the weight and shape of the vehicle surrounding it, every engine has a range in every gear where it's got to "work harder" (i.e. requires excessive throttle opening) to maintain speed or accelerate. Below that point the vehicle will slow down despite a wide throttle opening. Because of common torque curve characteristics, this point will tend to be lower on larger displacement engines and higher on smaller ones (I realize I'm generalizing here). Thus a heavy Suburban with a 454 ci can cruise along at 2000 rpm at highway speed while a Civic with a 1.8 liter cruises around 2800-3000 rpm instead. But what consequences does attempting to cruise at a lower engine speed have? Is that civic engine being damaged trying to pull up a hill on the highway at 2500 RPM at 60 mph? If lubrication is OK, will this harm the bearings, rods, and other load-bearing components? Clearly this is "running the engine hard" but is it really harmful?
Wow, this turned out longer than I thought it would...
In short, what exactly does "lugging" mean, and what damage does running an engine at higher load/lower rpm actually do?
But I've always been cautioned to avoid lugging an engine and that's given be a little bit of irrational fear of running the engine at too low a speed. I've got some understanding of the reasoning behind this but there are lots of holes. In my detail-obsessive post of the week, I'd like to clear some of those up. What are the problems connected with running an engine at too low a speed, and how exactly does the term "lugging" apply?
One clear problem is that there's a point at which the engine is spinning just fast enough to maintain adequate oil pressure. This point must vary based on engine/oil pump design, and to run the engine below that point would cause lubrication problems. It's not clear to me that this point should have too much correlation with displacement, so presumably it would be close to the same whether you're talking about a 6 liter V8 or a 1.5 liter 4 banger. Correct?
Depending on engine displacement and tuning, every engine has a unique torque curve. Thus, depending on the weight and shape of the vehicle surrounding it, every engine has a range in every gear where it's got to "work harder" (i.e. requires excessive throttle opening) to maintain speed or accelerate. Below that point the vehicle will slow down despite a wide throttle opening. Because of common torque curve characteristics, this point will tend to be lower on larger displacement engines and higher on smaller ones (I realize I'm generalizing here). Thus a heavy Suburban with a 454 ci can cruise along at 2000 rpm at highway speed while a Civic with a 1.8 liter cruises around 2800-3000 rpm instead. But what consequences does attempting to cruise at a lower engine speed have? Is that civic engine being damaged trying to pull up a hill on the highway at 2500 RPM at 60 mph? If lubrication is OK, will this harm the bearings, rods, and other load-bearing components? Clearly this is "running the engine hard" but is it really harmful?
Wow, this turned out longer than I thought it would...
In short, what exactly does "lugging" mean, and what damage does running an engine at higher load/lower rpm actually do?