What RPM do you consider lugging at WOT?
- Thread starter Avery4
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Reminds me of my long passed grandad. One of the last cars he had was an early 90's Subaru Legacy station wagon with the 5 speed. He couldn't get it into 5th fast enough. Usually shifted it 1/3/5 and was in 5th before he was rolling 20mph. That think clanked and bucked like you wouldn't believe, but he drove it like that until just before he passed in 2003. The car still ran, although I'd have been super interested to pull the motor and see what it looked like on the inside. I spent many summers just cruising around with him, usually looking at fields where he had an arrangement with most of the local farmers to hunt their groundhogs, so tons of slow speed putting around...in 5th usually. He'd only downshift if the thing threatened to stall going up a hill. He took lugging to the extreme with that poor car, but it kept going.
Unless you are running E85 ;-)
I have actually looked for that, but I was never able to find one. I suppose the graph would be very specific to the engine design, oil and oiling system design, operating temp, and the specific part, but still interesting to see nonetheless. Some parts such as the valvetrain wouldn't be directly affected by the engine being overloaded/lugged while the bottom end certainly could be.
If lugging is anything under 2-3000 rpm you have to wonder why there are so many modern forced induction engines that develop maximum torque at 1500 rpm. I can't say I've ever used full throttle at 1500 rpm but it must be possible and you have to assume the manufacturers would approve if I did otherwise what's the point of producing an engine to that specification.
I assume that forced induction engines must have larger diameter crank bearings in order to give hydrodynamic lubrication a chance to produce an adequate oil film thickness at such low revs.
I assume that forced induction engines must have larger diameter crank bearings in order to give hydrodynamic lubrication a chance to produce an adequate oil film thickness at such low revs.
Lugging is being in too high of a gear and unable to accelerate. Usually below 1500 rpm
I'd have to say anything under peak BSFC, that is, the most efficient spot in the rev band. Anything over that is, well, revving. 
Is it dangerous? Well, no, unless you take it to extremes. But if you drop a gear and get in a better spot in the power- and efficiency band there's no reason not to.
I used to accelerate my saturn by putting the pedal halfway down and upshifting when my acceleration rate was more than I wanted. This led to staying in 3rd up to 65+ plenty of times. Retired that car at 244k with a whole bunch of simultaneous failures-- but the engine wasn't one of them.
Is it dangerous? Well, no, unless you take it to extremes. But if you drop a gear and get in a better spot in the power- and efficiency band there's no reason not to.
I used to accelerate my saturn by putting the pedal halfway down and upshifting when my acceleration rate was more than I wanted. This led to staying in 3rd up to 65+ plenty of times. Retired that car at 244k with a whole bunch of simultaneous failures-- but the engine wasn't one of them.
I use WOT in my 335i and my other half's '14 Focus in manual mode below 2k, no problem. With modern ECUs I don't think this is even a question.
I've seen graphs that show more ring wear as the RPM increases - other variables held constant. And you're right that some engine components like valve train and journal bearings aren't as wear sensitive to RPM like rings are. Journal bearing MOFT actually increases with RPM, but the actual instantaneous viscosity in a journal bearing also decreases at the same time due to shearing and heating. That's why HTHS viscosity is important.
Max torque point on the torque curve is typicalky also the maximum volumetric efficiency point (ie, the maximum cylinder charging efficiency).
WOT with forced induction at 1500-2000 RPM is also the LSPI danger zone on some engines.
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^^This. I didn't think you could even lug a modern engine.
On BITOG “modern” goes back a few decades. Some of have cars old enough to vote. Or at least display some teen angst and pouting.
I agree if it is equipped with an A/T, but a modern engine bolted to a manual transmission with an inexperienced driver can easily be lugged.
Modern to me means throttle by wire.
Lugging to me means putting enough load on an engine at low rpms ( from pounding on the bottom end bearings.
Lugging to me means putting enough load on an engine at low rpms ( from pounding on the bottom end bearings.
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Nope. I have a 6 speed manual CX-5. Watching the real time fuel consumption reading in a high gear it hits a maximum point and will not go over that. For example, in 5th gear at 35mph it will run at 1800rpm or so. The fuel consumption goes up through the first third of the throttle travel and then not change until the rpm slowly rise and the fuel consumption rises linearly with rpm. Seeing that all modern vehicles are computer controlled, the throttle butterfly is not connected to the pedal at all. No matter if I’m at 1/2 throttle or floored, the computer is maintaining a stoichiometric fuel ratio around 14:1 by adjusting injector timing and butterfly position. It will not lug.
My truck on the other hand will try to maintain 1100-1200 rpm up hills by spooling the turbos and can feel quite rough until it downshifts. Not to the point of knocking, but the stock tuning is weird at times...holding gears woo long before downshifting. Sport mode removes that issue luckily. I have probably floored the truck 2 or 3 times since I’ve owned it. There is simply no need, even towing 7500 lbs, and super-legal speeds arrive much too quickly.
Good to know. What happens if you accidentally were to shift into 6th gear at 20 mph and floor it? I can't imagine there not being some lugging occurring while the computer tries to compensate for driver error. Having said that I haven't lugged an engine since the 1970's when I first learned to drive a stick, so these engine management/protection systems might really be dialed in.
In my experience, and that ranges from diesel farm equipment, tractors, two stroke motorcycles carbed engines and modern computer controlled and DBW throttle vehicles, the engine will let you know when it is being lugged, truly lugged. Usually there will be shaking, bucking, lurching and the sound of the engine will change dramatically. One would have to be totally oblivious to ignore these signs. I’ve seen engines that would not lug until around 500rpm, others like my 95 2.2 Accord, weren’t happy below 1500rpm.
The discussion on various forums, from my experience usually revolves around “theoretical lugging” and it’s clear that a lot of people don’t have experience what a truly lugged engine does and sounds like. That is why all they want to know is some arbitrary “safe” RPM range. There is no such thing.
The discussion on various forums, from my experience usually revolves around “theoretical lugging” and it’s clear that a lot of people don’t have experience what a truly lugged engine does and sounds like. That is why all they want to know is some arbitrary “safe” RPM range. There is no such thing.
