lugging a Porsche engine

[ricochet]

I know lugging a Porsche is taboo, have known this since my cousin let me drive his P-cars back in the early 70's. I have never LUGGED my P-car, I tend to keep 2500-3000 RPM minimum (except at start).
I searched for an hour or so, got this definition which I accept-> Lugging is when you have too much throttle for the RPM you're at. Coasting down in gear until the engine is at idle speed is not lugging neither is idling along at 1500 RPM. Just be easy on the gas until the engine speed increases.

Just what does lugging a Porsche motor do? I accept it destroys the motor, but how? I raced motocross and also drag bikes (all 2 stroke, a FEW years back), I know how low rpms killed 2 strokes, I NEVER fouled plugs. I never lug High performance stuff, but do lug Fords for many k miles.

But, I accept fouling plugs ain't the problem with Porsches. I am sure in an hour I will understand what lugging does to a Porsche engine and how? Thanks. I did try a search, found just don't lug the motor again and again. How does lugging hurt and what parts. Forgive my ignorance, I just started thinking at dinner, I never asked why?

[Hoffman912]

in a 356 or 912 motor its usually the crank that gets hurt.

[ricochet]

Thanks Harry,
heard lugging hurts the lowers before, but AGAIN I never asked how or why! In my dyslexic thinking, I'd assumed this would hurt the uppers more. C'mon guys. You know what I want to understand, but don't.

[LakeCleElum]

The flat six needs revs to get the oil pressure up and get sufficient oil to the pistons and cams. More RPM's also means turning the fan faster and better cooling. Since the engine is cooled by both air and oil, keep it spinning. Serious lugging will damage bottom end bearings in any engine....

[ricochet]

Thanks Bob,
I accept your info as correct, think more stuff to be offered going deeper. The fan goes faster, the oil circulates better, I accept these work better at RPMs. BUT, I believe these answers are simpler than what really happens. Lugging a Porshe engine is so much different than lugging a 400k Ford truck engine (have done that a couple times with no ill effects, those seem to like lugging).

I love my Porsche, never under-rev it, nor lug it. But I want a simplified description of what happens and why! No engineering report, but something a non-engineer can understand.
Cooling info is great (the air and water), but with everything else being correct, what does lugging a Porsche motor do damage to?

[ianc]

Hey Ricochet,

I have been at odds with some people here who believe that the higher you rev, the better the engine likes it. For myself, this seems nonsensical. Contrary to earlier claims, you'll find that even though the fan is running faster at higher RPM's, the engine will run hotter and consume more fuel doing it. My philosophy is that you never want to lug the motor, but to over rev the motor pointlessly will stress it and cause it to wear or fail more quickly.

As to the guts of your question, it is something I think a lot of us have a kind of gut feeling about, but would have a difficult time explaining logically.

Drivers of the older Porsche racing 4 cylinders with roller bearing mains were advised to always keep the revs up since running them at lower RPM's caused eventual deformation of the roller bearings.

It's an interesting question. My theory is that as a cylinder fires and pushes the piston down in it's bore, the force is transmitted to the mains. If the engine is spinning over faster, the force is tranmsitted more uniformly over the bearing surfaces, whereas if it's moving more slowly, the force is concentrated over a smaller area of the bearing, which of course will cause it to wear or deform more rapidly.

The vibrations and horrible noises associated with doing this would cause any right-thinking person to avoid it, but as for an actual scholarly analysis, I'm afraid the above is the best I have to offer.

Looking forward to more interesting responses,

ianc

[Wayne 962]

At low RPMs, the engine is fighting the mass of the car when firing the pistons and cylinders. They have to move backwards to relieve pressure in the cylinder. If it can't easily move backwards, it places a lot of stress on the engine components, like the crank.

It's very much like doing leg presses in the gym. If you have a reasonable amount of weight, you can push against it. If you put a ton of weight on the leg presses, and then try to push on it, chances are you will pull a muscle or hurt yourself.

That said, the 911 cranks are very strong and I have never heard of one being hurt by lugging. As people have pointed out, this is a common problem with 356 and 912 cranks (they crack).

-Wayne

[john_colasante]

The 993 owners manual tells you not to lug the engine.

[2.7RACER]

Lugging your motor is like trying to pedal a ten speed bike in high gear. All your weight goes against the pedals with very little mechanical advantage to propel the bike. The load on the pedals is very high as compared to shifting down to a low gear. Same for the con rod bearings and piston pins. The high loads displace the oil film and you can get metal to metal contact and thus wear.
You can imagine if you were able to provide enough force to the bicycle pedals you could break them. Same for a motor.

[snowman]

More clarification (hopefully) of lugging. A rod bearing and main bearing depend on a film of oil to seperate the moving metal surfaces, sort of like hydroplaining your car tires on a rain slick road. Except in this case hydroplaning is a good thing. The faster the parts move the easier it is to keep up the hydroplaning (please excuse spelling). If the parts are moving to slowly they can make contact with each other and extreem wear happens. If the engine is just loafing along there is no problem, but a Porsche has a very large ammount of power available and if you open it all the way up at very low speed and high load you will completely squeeze out the oil film seperating the moving parts. Imagine hitting the top of the piston and connecting rod with a sledge hammer. At higher engine speeds most of the force is used up just to keep up with things and the rest of the force just adds a little more to whats going on already. also its almost impossible to overcome the "hydroplaning" at high speeds.

Hope this makes some sense to you and helps.

[HardDrive]

Got it. No lugging. I'll make sure to keep it above 5000 at all times.

[livi]

Great explanations ! I have allways wondered what the heck the term lugging really meant. So I guess you could formulate an equation here:

Lugging = throttleload x gear / RPM x speed

Right ??

Markus
Carerra 85

[ricochet]

Thank you guys,
I now have a MUCH better understanding of the damage caused and how is caused by "LUGGING". I appreciate all your help...

[randywebb]

re oil film -- where is island when we need him?

I've 'always' known what it is caused by but in all these decades never knew the mechanistic process that caused the noise....

So it seems that too much stress at too low a rotational crank speed prevents complete lubrication of the crank (?)
And, is the crank in a stick/slip condition? Is that what the noise is?

BTW - Google didn't turn up any good definition/explanations. It's bound to be in some engine book or the other tho...

[ricochet]

Originally posted by HardDrive
Got it. No lugging. I'll make sure to keep it above 5000 at all times.

Hey HardDrive, I don't think that is the solution. I did learn a LOT from the posts here, all things were appreciated. The hydraplaning aspect offered the most simple explanation of the lower damage causes, but all things considered I guess I now know why Porsche says "Don't lug the engine". Is complex, yet you guys offered great info that explains things that a guy like me can understand. I'll keep doing as I did for years, I won't lug the motor.

[M.D. Holloway]

Bump

[Paul Ferradas]

After reading all this I still don't know what lugging means

[randywebb]

1. feels like a bad vibration
2. happens at low rpm
3. happens at high load (i.e. motor won't lug if it is at idle w/no load despite #2 above)

how's that?

[Paul Ferradas]

Ah yes, that weird sound that it makes, almost like a rattle. I always wondered what that was. The PO warned me not to be alarmed and most Porsche's make this sound.

My friends Camaro does the same thing.

[jester911]

Most lugging occurs when too high a gear is selected for the speed the car is going. An example would be to shift to 3rd while doing 20 mph. There are other ways to make it lug but that is the most common way it happens.

It can be done in most any manual shift car.