Downshifting
05-20-2008, 10:50 PM
#1
Downshifting I was going around 37mph in 5th gear and started to slow down for a turn. As I went around the turn, I dropped to about 18mph, but forgot to downshift. After the turn, I lightly stepped on the gas pedal for about a second in 5th gear at 18mph and immediately let go when the car vibrated with a deep hum.
I understand what this is, but I just wanted to know the longterm damage that's done to the engine. Does the vibration shake things loose? Or is the effect neglegible at minor occurances (light gas/short time) where the driver can afford to make the mistake of not downshifting?
(This is an LS1 V8 M6.)
I appreciate any input.
I understand what this is, but I just wanted to know the longterm damage that's done to the engine. Does the vibration shake things loose? Or is the effect neglegible at minor occurances (light gas/short time) where the driver can afford to make the mistake of not downshifting?
(This is an LS1 V8 M6.)
I appreciate any input.
05-20-2008, 11:16 PM
#4
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It's called "lugging" the engine, and it is very hard on the internal parts of the engine. If you do it alot you can cause engine damage. Try to remember to downshift the trans if you can.
05-20-2008, 11:20 PM
#5
Ah, so that's what it's called. I kept trying to find a single term to describe this instead of having to tell a whole paragraph. LOL
I keep a sharp memory on all the wrong things to do when driving this car. Now lugging is added to the list and I definitely will be keeping a watch over my own shoulder on avoiding this.
Thanks for chiming in.
I keep a sharp memory on all the wrong things to do when driving this car. Now lugging is added to the list and I definitely will be keeping a watch over my own shoulder on avoiding this.
Thanks for chiming in.
05-21-2008, 12:09 AM
#6
Is taking off from a stop with too much clutch and not enough gas also lugging?
I did a quick search on Yahoo!, and from what I've found so far, it appears that the damaging components of lugging is principally overheating in the cylinders. As such, what are the requirements for the sufficient amount of overheating to "melt" the pistons and cause any other subsequent damage? Does it require a specific amount of gas and time during an under-leverage of gear ratio (high gear/low speed) to cause rapid overheating, or is immediate upon pre-ignition?
I did a quick search on Yahoo!, and from what I've found so far, it appears that the damaging components of lugging is principally overheating in the cylinders. As such, what are the requirements for the sufficient amount of overheating to "melt" the pistons and cause any other subsequent damage? Does it require a specific amount of gas and time during an under-leverage of gear ratio (high gear/low speed) to cause rapid overheating, or is immediate upon pre-ignition?
05-21-2008, 12:16 AM
#7
don't worry about it. I've done that by mistake on several occasions, and no ill effects after 93000 miles lol.
and yes, not giving enough throttle from a stop does count as lugging. You'll know you're doing it b/c you will get a slight rattling sound from the engine
and yes, not giving enough throttle from a stop does count as lugging. You'll know you're doing it b/c you will get a slight rattling sound from the engine
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05-21-2008, 02:34 AM
#8
Before my TA, I had never driven a manual before, and the idea I got from a YouTube video is that with most cars, you can let up the clutch slow to get the car moving without having to step on the gas, and that it's OK as long as the engine doesn't stall. Now I understand it all depends on how fast you want to take off. But if I take off in 1st from stop for a gradual acceleration without gas, I can still hear a light hum when the clutch is fully engaged. At this point, the RPM drops to about 3-400 for a split second. The engine stress level is obviously different from my mistake in the first post, but is it still the type of lugging that damages the engine in time? If so, how long does it take if it were habitually practiced.
I've since been taking off the right way by giving gas with clutch. I just want to know what possible consequences the first few months of doing this (driven every other day/not daily driven) might've caused.
I've since been taking off the right way by giving gas with clutch. I just want to know what possible consequences the first few months of doing this (driven every other day/not daily driven) might've caused.
05-22-2008, 01:42 AM
#11
You mean preignition during the compression stroke?
Do you necessarily have to feel a jerk for every preignition? I didn't feel any reverse jerking, but I want to get an idea if my lugging incident included a preignition.
By the way, the F-body cars are equipped with a skip shift, which requires you to go from 1st to 4th at any speed above 15mph. No matter the conditions, wouldn't there ultimately be a bit of lugging each time you skip shift?
Do you necessarily have to feel a jerk for every preignition? I didn't feel any reverse jerking, but I want to get an idea if my lugging incident included a preignition.
By the way, the F-body cars are equipped with a skip shift, which requires you to go from 1st to 4th at any speed above 15mph. No matter the conditions, wouldn't there ultimately be a bit of lugging each time you skip shift?
05-22-2008, 02:58 AM
#13
So GM put this in to help save on gas, but only to have to divert the savings to a new engine? How thoughtful.
My skip shift is eliminated, but I manually skip shift when I'm on flat ground and when the light goes on. I usually get into 4th at around 18mph, then use low throttle acceleration to an optimum RPM before shifting into 5th (usually by 35mph), and I don't hear any growl in any of the gears. Am I lugging the engine even when there's no growl?
My skip shift is eliminated, but I manually skip shift when I'm on flat ground and when the light goes on. I usually get into 4th at around 18mph, then use low throttle acceleration to an optimum RPM before shifting into 5th (usually by 35mph), and I don't hear any growl in any of the gears. Am I lugging the engine even when there's no growl?
05-22-2008, 04:46 AM
#15
TECH Resident
It's definitely not something you wanna do all the time, but once shouldn't hurt anything. It's kinda like grinding a gear in your tranny. Do it a ton and you've got a problem on your hands. Do it once in a while and you shouldn't have a problem.
Actually, it was to avoid the gas guzzler tax.
So GM put this in to help save on gas, but only to have to divert the savings to a new engine? How thoughtful.
My skip shift is eliminated, but I manually skip shift when I'm on flat ground and when the light goes on. I usually get into 4th at around 18mph, then use low throttle acceleration to an optimum RPM before shifting into 5th (usually by 35mph), and I don't hear any growl in any of the gears. Am I lugging the engine even when there's no growl?
My skip shift is eliminated, but I manually skip shift when I'm on flat ground and when the light goes on. I usually get into 4th at around 18mph, then use low throttle acceleration to an optimum RPM before shifting into 5th (usually by 35mph), and I don't hear any growl in any of the gears. Am I lugging the engine even when there's no growl?
Actually, it was to avoid the gas guzzler tax.
05-22-2008, 09:04 AM
#17
Yeah, worst case scenario is a little knock or ping while lugging the motor. Unless you make a habit o fit, should not cause any ill effects. In fact, its quite popular for people to lug their motors when trying to diagnose a slipping clutch. I wouldnt worry about it.
05-22-2008, 02:53 PM
#18
I just spoke with a tech from the dealership, and he mentioned that lugging constitutes the risk of tearing the piston rings, but he wasn't clear on how proned this is to happen during lugging.
Is pressure from a 5th gear lugging sufficient to blow a piston ring?
I didn't hear any knocking or pinging, but are they generated upon preignition or detonation?
Is pressure from a 5th gear lugging sufficient to blow a piston ring?
I didn't hear any knocking or pinging, but are they generated upon preignition or detonation?
05-22-2008, 04:37 PM
#19
I just spoke with a tech from the dealership, and he mentioned that lugging constitutes the risk of tearing the piston rings, but he wasn't clear on how proned this is to happen during lugging.
Is pressure from a 5th gear lugging sufficient to blow a piston ring?
I didn't hear any knocking or pinging, but are they generated upon preignition or detonation?
Is pressure from a 5th gear lugging sufficient to blow a piston ring?
I didn't hear any knocking or pinging, but are they generated upon preignition or detonation?
05-22-2008, 04:58 PM
#20
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Just don't make a habit of lugging the engine and you will be fine.
Keep in mind that Detonation and Pre-Ignition are related, but different.
* Detonation - An uncontrolled burn, which is usually audible and results in VERY high pressures in the cylinder.
* Pre-ignition - Can CAUSE detonation, but is typically a hot spot (possibly carbon), or another situation that ignites the air/fuel mixture before it is intended to be ignited.
Detonation causes very high cylinder pressures because the flame front does not progress as intended, it literally explodes.
Pre-ignition actually lights the mixture too far before Top dead center, thus actually trying to push the piston back down and turn the crankshaft the opposite direction.
Another related topic is the "ping" that people complain about when they use lower octane fuel. The higher octane actually slows down the rate at which the fuel burns, slowing the flame front. Lower octane fuel is unable to do that. This is why our engines have knock sensors..... if they detect any "ping", the computer retards the ignition timing to reduce cylinder pressures and protect the engine. Of course, this results in less power and the use of more fuel to make power......
Keep in mind that Detonation and Pre-Ignition are related, but different.
* Detonation - An uncontrolled burn, which is usually audible and results in VERY high pressures in the cylinder.
* Pre-ignition - Can CAUSE detonation, but is typically a hot spot (possibly carbon), or another situation that ignites the air/fuel mixture before it is intended to be ignited.
Detonation causes very high cylinder pressures because the flame front does not progress as intended, it literally explodes.
Pre-ignition actually lights the mixture too far before Top dead center, thus actually trying to push the piston back down and turn the crankshaft the opposite direction.
Another related topic is the "ping" that people complain about when they use lower octane fuel. The higher octane actually slows down the rate at which the fuel burns, slowing the flame front. Lower octane fuel is unable to do that. This is why our engines have knock sensors..... if they detect any "ping", the computer retards the ignition timing to reduce cylinder pressures and protect the engine. Of course, this results in less power and the use of more fuel to make power......