[bestclimb]

Originally Posted by d0sitmatr

most likely as with an auto if it starts to bog on you, the trans downshifts, with a manual, you could end up damaging the engine if you refuse to downshift.
thats the best reason I can come up with.

Someone would have to be pretty brain dead to not understand what the engine is telling you long before you can do any damage. I can do the same thing <20mph in 5th in most cars.

Originally Posted by Leadfoot

If they built it with special piston rings and cylinders as they do marine engines, then you could bog that motor down all day. I believe marine engines also use special bearings.

Not so much. A marine engine is built to run at a higher power setting for long durations. As in 80% load at 3500 rpm. They use heavier duty bearings, better internal oiling, and increased cooling to deal with the higher internal temperatures and higher average stresses that they are submitted to continuously.

The bogging and chugging you get when you lug an engine is due to the spark happening before top dead center, and with lower speed the piston is not far enough past top dead center when the pressure of the expanding fuel charge is increasing. So instead of adding a push down the burning fuel charge puts a stopping pressure on the piston and the momentum of the engine and previous combustion in other cylinders forces the "lugged" cylinder over the top and down.

This increase in resistance coupled with low oil pressure (because the engine driven oil pump is not turning very fast) causes the rod bearings to squish all the oil out and the bearing surfaces come into contact.

A marine engine with better bearings can withstand this for longer (though it would not likely be subjected to this as water is a viscous medium to transmit power to rather than a tire/road interface) but it is still bad for it.