How do you lug an engine with an automatic transmission?
RPMs affect on engine longevity
- Thread starter Razl
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I've seen auto trannies in overdrive at 40 MPH and the tach under 2000 RPM.
GM V8's, starting with the 5.7L, are notorious for being "luggers".
My 2001 5.3L Vortec cruises at 60 mph in 4th(overdrive) with only 1700 rpm.
After the tranny shifts into 4th at 45-50 mph, I can back off the gas and do 40 mph, on a level road, at only 1200/1300 rpm!
My 2001 5.3L Vortec cruises at 60 mph in 4th(overdrive) with only 1700 rpm.
After the tranny shifts into 4th at 45-50 mph, I can back off the gas and do 40 mph, on a level road, at only 1200/1300 rpm!
You don't unless you have your computer plugged in and don't let it unlock the torque convertor or downshift.
Remember, guys, that there is nothing inherently destructive about running an Otto-cycle (4-stroke) engine at "low" rpm with a wide open throttle. The lugging is bad thing stems from engine design that does not have sufficient lubrication pressure or flow or similar cooling system issues lower in its rev range. Current (American at least) engine designs are much better about getting proper lubrication and cooling at lower rpms. Remember also that highest cycle efficiency (correlates to fuel efficiency) in an Otto-cycle engine is achieved at low rpm and high throttle opening.
Not necessarily. My Prelude runs 3000 rpm @60mph and redlines at 6500rpm with a 3.19" bore and 3.74" stroke. My 1969 Saab turned 3200rpm at 60mph and redlined at 5200rpm with a 3.54" bore and 2.59" stroke. The Honda is definately a long-stroke engine, but because of the valvetrain geometry, it can handle higher rpms than the Saab.
I can't compare the wear/longeviety between the two cars because of unknown prior owner maintenance, but it is my understanding that long-stroke engines typically wear out the rings faster because of the much higher piston speeds. For each revolution, the Honda piston has to travel 3.74" x 2 = 7.48" x 3000rpm = 22,440 inches per second vs. the Saab piston travelling 2.59" x 2 = 5.18" x 3200 rpm = 16,576 inches per second. Faster piston speed = more friction on the rings and higher heat buildup.
It's back to engine design school for you, Kreigle, for four reasons: your units don't work out, the piston moves the stroke length four times, not two, per revolution, you have only attempted to calculate average piston speed as opposed to maximum (sinusoid, right?), and fourth, to make your point, you're not seriously comparing a German Ford V4, the worst of the sixties, with a Honda inline 4-cyl, considered one of the most high tech engines of the nineties, are you? Now, a SAAB 2-stroke would have been another story...
But sure, it's generally true that faster piston speed equals more friction and heat, and therefore wear...
Also, XS650 did say 'usually.'
But sure, it's generally true that faster piston speed equals more friction and heat, and therefore wear...
Also, XS650 did say 'usually.'
Hi,
over the years the definition of "lugging" has been dicussed with great fervour in trucking circles!
Generally now it is accepted as the point where a wide open throttle produces no accelleration
bulwnkl correctly said;
"Remember also that highest cycle efficiency (correlates to fuel efficiency) in an Otto-cycle engine is achieved at low rpm and high throttle opening."
Many modern heavy diesel engines produce maximum torque at around 1100-1200rpm and this remains constant out to around maximum operating revs - say 1550-1650rpm. (This encourages much running at near full "throttle") Gearing is arranged to provide max road speed (100kmh here) at about 1650-1900rpm depending on application
Gearing for low revs and designing for maximum torque around 1100 was pioneered by Mack/Scania This was developed by MB (the worlds largest diesel engine maker) from about 1975 and introduced in the marketplace from about 1980
This has been greatly facilitated by the use of advanced ECMs with enormous (for a motor vehicle) computing capacity. This is now being coupled to advanced electronically controlled "manual" transmissions. This enables more running in the true fuel economy range
MB now employ the same principles in their new petrol engine families
Regards
Doug
over the years the definition of "lugging" has been dicussed with great fervour in trucking circles!
Generally now it is accepted as the point where a wide open throttle produces no accelleration
bulwnkl correctly said;
"Remember also that highest cycle efficiency (correlates to fuel efficiency) in an Otto-cycle engine is achieved at low rpm and high throttle opening."
Many modern heavy diesel engines produce maximum torque at around 1100-1200rpm and this remains constant out to around maximum operating revs - say 1550-1650rpm. (This encourages much running at near full "throttle") Gearing is arranged to provide max road speed (100kmh here) at about 1650-1900rpm depending on application
Gearing for low revs and designing for maximum torque around 1100 was pioneered by Mack/Scania This was developed by MB (the worlds largest diesel engine maker) from about 1975 and introduced in the marketplace from about 1980
This has been greatly facilitated by the use of advanced ECMs with enormous (for a motor vehicle) computing capacity. This is now being coupled to advanced electronically controlled "manual" transmissions. This enables more running in the true fuel economy range
MB now employ the same principles in their new petrol engine families
Regards
Doug
I have a nice article in front of me about what pushing an engine to it's maximum revs can do for longevity.
Autoweek - Sept27 2004 has an article about being able to purchase older, out-of-use Ferrari F1 cars.
The employees at Ferrari that look after them for the buyers, generally recommend short shifting them by 1,000 rpm.
Bottom line from the Ferrari staff, "we always suggest to be quiet on the revs, because maybe the life is going to be bigger". And the article adds, "He reckons that short-shifting by 1,000rpm can at least double the distance-before-overhaul"
The life of the full out race engine is about 372 miles(600km).
Autoweek - Sept27 2004 has an article about being able to purchase older, out-of-use Ferrari F1 cars.
The employees at Ferrari that look after them for the buyers, generally recommend short shifting them by 1,000 rpm.
Bottom line from the Ferrari staff, "we always suggest to be quiet on the revs, because maybe the life is going to be bigger". And the article adds, "He reckons that short-shifting by 1,000rpm can at least double the distance-before-overhaul"
The life of the full out race engine is about 372 miles(600km).
My car revs 1100 RPM at 40MPH and 2000 RPM at 70MPH. If you give it gas to the point just before it downshifts you can hear a slight lugging sound. I usually keep it in overdrive if it is already in overdrive and I don't need to pass anyone, so it does get 'lugged' from 50MPH to 75MPH on a daily basis as I pull from the busy highway near my house to the interstate. Once it passes 1,500 RPM(55MPH) it isn't luggy. It does save gas though.
I really enjoy this post! When I had a 64 MG Midget it would run 4000 rpm at 60 mph! I drove it from Cincinnati to New Orleans and kept it about 5000 rpm almost the whole way. Couldn't handle that kind of trip today in that small of a car. The good old days! I also remember reading that while wear does increase with the square of the speed, there is a point at low rpm where the wear(stress?) on the bearings increases suddenly and can be much greater that what occurs at high revs... Don't think I am stating that the way I want to....I am impressed with how well some of you explain this stuff. It really gets confusing when you start comparing things like big truck diesels too. Apples and oranges? But all very interesting reading.
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