Lugging the engine - good or bad for economy?

[dcb]

The engine load is an exponential function of rpm, but I don't know that the increase in the oil layer also offers exponential cushioning. There is a graph there somewhere which would answer your concern for landspeeds bearings, but I don't know if it is a valid concern without seeing it.

re: accumulator, I was just thinking upside down 2-liter and a solenoid tapped into the oil pump with a restriction and check valve to fill it

Again the term lugged has surfaced, from a murrican referring to an english document. What do you suppose the article meant by "lugged"? I don't think landspeed mentioned anything about 180RPM

Oh, and reality check, last I checked a set of bearings are like $20. Us murricans need to be more self sufficient anywho.

And "the engine might not even be making that much torque at low RPM" part means just that. Here's a picture, it is a pretty steep climb until 3000RPM for this engine:

[PaleMelanesian]

Yeah, but at 1250 rpm it's already making more than my car's peak horsepower. More than enough. Step up to about 1500 to account for it being a heavier car.

[ttoyoda]

re: accumulator, I was just thinking upside down 2-liter and a solenoid tapped into the oil pump with a restriction and check valve to fill it

I would be fascinated to see the results if you go ahead and do that. Please post pictures of before and after. If you could take a video of the "during" and put it up on youtube that would be great.

The engine load is an exponential function of rpm,

No, it goes up as the square. It does not go up as e^rpm.
"exponential" does not mean the same as "squared", so you did not bother to read the links.

Oh, and reality check, last I checked a set of bearings are like $20.

LOL, you have never put a set of bearings in. If you had ever done the job, you would know that the amount of labor time makes the cost of the bearings unimportant.

Look at your chart. The minimum RPM the data is presented at is 1100. Why do you think that might be?

Tell you what, though. You just go ahead and run your engine how you see fit. My work here is done.

[sickpuppy318]

Pull that sucker on the ramps and drop the pan. I bet HE could rebuild that whole bottom end in about an hour. Not me, i'm not that good.

[aerohead]

Originally Posted by sickpuppy318

my old '88 toyota had a internal gear "gearoter" oil pump, and being positive displacement, had output pressure directly proportional to engine speed. So while engine loads decrease with RPM, so did oil pressure. It lugged a lot more than my mazda does now....

now after reading these articles, i realize that the lugging "jerk" at low RPM/high throttle is litterally the crank being thrown into the side of the bearing. ...not good.

OK, so now i guess i'll feather it past the "lug line", but have more confidence lugging around below it. slow and easy, not slow and WOT.

sickpuppy,I think your's was the first use of the term "jerk",which I understand as an "instantaneous acceleration." Under some of the extreme "lugging" scenarios mentioned,I understand that if jerk occurs,the bearing journal can actually displace the oil film,achieving "high-point",where there exists momentary metal-to-metal contact between the journal and babbit material.Instantaneous friction-welding and then fracture-release can occur,and this is basically the beginning of the end for both surfaces.I have been told that the switch to automatic transmissions for Diesels,has happened in part do to broken crankshafts due to "jerk",when operators let rpm's drop too low.Evidently,the torque-converter on an automatic will stall before rpm's can drop to a level where jerk would occur,protecting the crank.

[sickpuppy318]

Well you your driving around at 500 RPM and giving yourself whiplash you'd have to expect engine damage... I think more relevant to this thread are the less apparent effects of "half-lugging". What about 1300 RPM? My car does this low shudder that sounds and feels like a powerfull 18 inch subwoofer at 25Hz. Besides for the new squeeks, what kind of engine damage have i done????

[landspeed]

Anyway, I did 800rpm WOT (and even got some positive turbo boost at about 950rpm ). And repeatedly did this for 10,000s of miles.

The reason my car survived this, as well as rapid EOCing (must have been 30,000 EOC cycles easily), may be due to the fact that the CA 8-valve engine is VERY tough anyway, and also that it was low compression, so the cylinder pressure loads were not that high.

On my 1.0 Micra, I did maybe 1000rpm at 60% throttle. My rule is, if the engine feels comfortable (apart from the fact that the power delivery is less smooth as it is at about 15Hz at 800rpm), then lug all you want. If the engine starts jerking at all stop, because that is when you can damage the crank and so on. I never did that in my car.

Another random point - when EOCing, bump-starting with ignition on is, in my opinion VERY bad for the engine. Doing this revs the engine straight up to 1500rpm+, and you are often accelerating at that point, with no oil in the bearings!. Better is what I did - ignition off, and gently tap the clutch up a few times, so RPM goes up to 80, then 150, then 300, then gently lift the clutch till you reach engine speed. Then, 0.5 seconds later, switch on the ignition. This is what I did, and the whole cycle took 1 second or so, once it became second nature.

[cookie96civic]

Lugging the engine is essentially opening the intake/throttle as wide as it gets (assuming heavy pedal pressure) with no response. Also is a nightmare of stress on your main bearings, which in a small 4cyl, are not that strong to begin with. better off redlining the engine than lugging it - MPG not considered

[mateospeed]

I realize I'm dragging up an old thread, but I need some clarification, and am hoping to get some here! Aerohead, can you provide a source for this information? I'd like to do some more reading on this idea.

I've been wondering what causes the "shaking" feeling when you lug an engine - this momentary welding and fracturing or the crank journal-to-bearing-surface would certainly explain it. Simple bearing contact would not!

Thanks!
-Mateospeed

Originally Posted by aerohead

sickpuppy,I think your's was the first use of the term "jerk",which I understand as an "instantaneous acceleration." Under some of the extreme "lugging" scenarios mentioned,I understand that if jerk occurs,the bearing journal can actually displace the oil film,achieving "high-point",where there exists momentary metal-to-metal contact between the journal and babbit material.Instantaneous friction-welding and then fracture-release can occur,and this is basically the beginning of the end for both surfaces.I have been told that the switch to automatic transmissions for Diesels,has happened in part do to broken crankshafts due to "jerk",when operators let rpm's drop too low.Evidently,the torque-converter on an automatic will stall before rpm's can drop to a level where jerk would occur,protecting the crank.