Hello everyone, I'm wondering about what RPM you guys would consider low enough to be damaging at full throttle. I have heard the general rule of thumb that with the exception of taking off from a stop in 1st gear, running the engine at full throttle under such a heavy load that it can't reach at least half of redline is potentially damaging to the engine and should be avoided at all costs. How true is this?
What RPM do you consider lugging at WOT?
- Thread starter Avery4
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Depends what oil you are running. high HTHS the lugging rpm window is smaller. Don't forget about fuel dilution either, which affects HTHS.
Probably also depends on gas or diesel. And when do you find a need for full throttle unless it's some underpowered econobox?
For the purpose of this discussion, let's assume that an old lady who knows nothing about cars and ignores advice from friends and family members who know about cars is driving an old gasoline powered economy car with a 4 cylinder engine and a 5 speed manual transmission and she's too lazy to downshift when she needs to pass someone or get up a hill, so she floors it in 5th gear at, say, 2K or 2500 RPM instead of downshifting like she has been told to do over a million times. How damaging would this be to the engine?
above 2K rpm, and warmed up...NOT at all damaging.
Generally speaking, 2500 RPM is not lugging in most gasoline engines. Of course Granny will accelerate much faster if she downshifts to 2nd or 3rd gear. But flooring it in top gear at 2500 RPM is not lugging and won't damage anything.
For most engines my anti-lugging general rule of thumb (what I taught my family) is don't use full throttle below 2,000 RPM. That works for most cars but of course, every general rule has its exceptions. But I also taught them that if you really need to go (freeway on-ramp, passing someone), downshift and use the top half of the RPM range. Revving the engine doesn't hurt it at all, but is actually good to use the full range and shift just below redline.
For most engines my anti-lugging general rule of thumb (what I taught my family) is don't use full throttle below 2,000 RPM. That works for most cars but of course, every general rule has its exceptions. But I also taught them that if you really need to go (freeway on-ramp, passing someone), downshift and use the top half of the RPM range. Revving the engine doesn't hurt it at all, but is actually good to use the full range and shift just below redline.
ls1mike
$50 Site Donor 2024
Towing with a gas truck. I have found it really depends on the engine. Like the WS6 or Caprice. You leave it in just about any gear without really lugging
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A vacuum gauge might be a useful addition to the dash.
Is it? With VVT and who knows what, I'm not sure if engines pull a lot of vacuum--I'm not really sure to be honest. But vacuum implies pumping loss, so I'd expect that to be minimized. [Arguing against myself, something has to make the vacuum for the brake booster.]
Assuming car has a knock sensor and backs off timing to reduce detonation, maybe nothing, maybe a little if done frequently. Computer can only do that in a limited range. If cylinder pressure rises too much you can damage the pistons and rings.
ls1mike
$50 Site Donor 2024
My truck is VVT.
What I'm wondering is, if between VVT and DBW, that pumping losses can be somehow minimized. Play with timing so as to hold the throttle blade more open, thus leading to lower vacuum for the same amount of fuel burn.
I remember reading years ago about how Chrysler used heavy amounts of EGR to do something similar, in that case I would think the throttle blade angle was unchanged but the amount of air flow past the blade was lessened. Hence the thought.
Atkinson cycle holds the valve open after TDC, no? That should have an effect on vacuum, and change how it should be interpreted.
If it can accelerate or at the very least keep the current speed, like when going up an incline, then it is not lugging.
Modern engine are almost impossible to lug due to computer controls.
Modern engine are almost impossible to lug due to computer controls.
ls1mike
$50 Site Donor 2024
Maybe, it certainly does not work in the Trans Am or Caprice, but they make enough torque it doesn't matter. You can be at 1200 RPM in 4th in the WS6 and floor it and it spins right up. The truck is different. It has a tune which eliminated a bunch of Nanny features. If I am on a hill or an on ramp and let it shift early while towing it is possible for it drop below 1800 RPM, while floored and still not lug even when towing.
Torque. That which I've been missing out on my whole life. Some day...
In my experience, gas engines with lower compression ratios are more tolerant of lugging compared to gas engines with higher compression ratios.
This mirrors my thoughts. With modern engine controls and the ability to pull timing to combat preignition/detonation, I don't think you're going to hurt anything unless you're really overdoing it.
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There is no general rule
It depends on the engine and what you are doing with it
I don't think the ol' lady has an issue at 2000-2500 rpm. Sorry, nothing to worry about. If she refused to downshift when at 500rpm, I'd worry.
I use full throttle at all rpms and never had an engine related failure. I see it as an ol' wives tail spread by ol' timers and the misinformed. But, all my engines have good oil pressure and quality oil. None detonate or rely on the knock sensor.
It depends on the engine and what you are doing with it
I don't think the ol' lady has an issue at 2000-2500 rpm. Sorry, nothing to worry about. If she refused to downshift when at 500rpm, I'd worry.
I use full throttle at all rpms and never had an engine related failure. I see it as an ol' wives tail spread by ol' timers and the misinformed. But, all my engines have good oil pressure and quality oil. None detonate or rely on the knock sensor.
