shifting to soon taking off at to low rpm bad for engine

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dakta1420
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shifting to soon taking off at to low rpm bad for engine

Post by dakta1420 »

So in class today we have been discussing diesels ect, well we were told a story where the guy would shift his cummins diesel at 1100 rpms ohr teacher said it would lug and buck. And he said that is hard on the rod bearings. I guess I never really thougnt about it but it makes sense, so can driving a stick to easy be detrimental to an engine?
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Re: shifting to soon taking off at to low rpm bad for engine

Post by theholycow »

Indeed, if it's bucking that's a surefire sign that your engine speed is too low. All that violent bucking is hard on the whole vehicle.

If the vehicle isn't telling you that your RPM is too low, then you're fine.
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Shadow
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Re: shifting to soon taking off at to low rpm bad for engine

Post by Shadow »

dakta1420 wrote:So in class today we have been discussing diesels ect, well we were told a story where the guy would shift his cummins diesel at 1100 rpms ohr teacher said it would lug and buck. And he said that is hard on the rod bearings. I guess I never really thougnt about it but it makes sense, so can driving a stick to easy be detrimental to an engine?

It's not really a matter of driving the vehicle "too easy"....it's more of being aware of the load you're putting on the engine. For example, I could shift my car all day at 1100 RPM and have no issue at all as long as I wasn't lugging (yup, there's that word again) the engine. Now I probably wouldn't want to do that while climbing up a hill, but on level ground and light throttle application, it would be just fine. I wouldn't be accelerating quickly at all, but I wouldn't be causing any problem with the engine either.
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Re: shifting to soon taking off at to low rpm bad for engine

Post by ClutchFork »

Lugging hammers your bearings and likely will squeeze the oil layer out to give milisecond events of metal on metal, which are not in themselves necessarily harmful, but cumulatively would be very bad. If your lugging results in bucking that is the worst.

I avoid lugging like the plague and typically don't like to even run my Ranger 2.3L below 2000 rpm, so will usually be in a lower gear at times than will the guy who is out for economy. This has the advantage though that if I want to move out I just step on it where the economy guy has to down shift first.

But you can accelerate from say 1000 rpm if the engine has enough torque and you go easy. As for diesels, I have zero experience, but understand they are made to operate at lower rpms and since they have about twice the compression of gasoline engines, they have much sturdier bearings. Well, my Ford 4.9L inline six was designed to act sort of like a diesel (or tractor engine) and would pull well right off idle, but you could certainly lug it if you put your foot in too hard.
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Re: shifting to soon taking off at to low rpm bad for engine

Post by tankinbeans »

No experience whatsoever as I tried short shifting once for economy, but got bored. Typically I shift at 2500 to 3000 and don't take much of a mileage hit, after all traveling at lower rpm to get up to speed over a longer distance uses a quantity of fuel and shifting high to get to speed more quickly uses another quantity of fuel. I'd be curious what the delta would be.
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Re: shifting to soon taking off at to low rpm bad for engine

Post by watkins »

The Cummins used in Rams can be shifted at 1100rpm with no problems. Been there, done that. First gear is also useless unless the truck is loaded or towing. Damn good engine.
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Re: shifting to soon taking off at to low rpm bad for engine

Post by IMBoring25 »

tankinbeans wrote:No experience whatsoever as I tried short shifting once for economy, but got bored. Typically I shift at 2500 to 3000 and don't take much of a mileage hit, after all traveling at lower rpm to get up to speed over a longer distance uses a quantity of fuel and shifting high to get to speed more quickly uses another quantity of fuel. I'd be curious what the delta would be.
There's some set of variables that's optimal for each vehicle and it's different for each one. My dad wondered once how I got the mileage I did when I drove the same vehicles he was. I was doing everything else quite similarly but accelerating a little harder and shifting a little higher. You reach a point where you're accelerating so gently the less time you spend steady-state getting good mileage overcomes the benefit, and he was past it.
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Re: shifting to soon taking off at to low rpm bad for engine

Post by monkeyhunk »

I've experimented on several tanks with mine and seem to do a little better letting it wind up a little more than short shifting. There is a point where too much rpm our accelerating to hard will drop the mileage too. It's been hard to get very conclusive data on that though because temperatures have have been all over the place or you may have 20 cm of snow barely plowed one day and black pavement the next. I haven't had this vehicle for a summer yet. That's when I'll actually get it figured out.
dakta1420
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Re: shifting to soon taking off at to low rpm bad for engine

Post by dakta1420 »

watkins wrote:The Cummins used in Rams can be shifted at 1100rpm with no problems. Been there, done that. First gear is also useless unless the truck is loaded or towing. Damn good engine.

This guy would shift it so quick he would be in 5th gear as 2-3 mph and he was mad as hell because it would buck. Especially going up hill. The governor is at 2750 and he said revving it above 1500 would blown it up.
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Re: shifting to soon taking off at to low rpm bad for engine

Post by watkins »

Well hes a dumb f*ck. The rev limiter is there for a reason. To limit you to safe revs. Its a nearly indestructible engine for the application. Hell, its a heavy duty engine shoehorned into medium duty trucks.
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