What speed do you use 5th gear ?

[someonestolecc]

It's not like idle because it's got load. A bigger load. While I have no scientific basis I'm almost sure that the load caused by too highly gearing an engine and making it struggle is worse than using the car as it was designed to run.

PS. love the new part of your sig, looks sweet.

[INASNT]

Ok so how is this 'load' physically hurting the engine... name parts exactly...

Trying to ride a mountain bike up a hill in a higher gear doesn’t actually physically damage me, I'm simply not able to do the same thing 'pedal legs' as fast as if in a lower gear, no damage, just reduced speed / power / torque.  

So now we come back to an engine, how is an engine different at lower speed as it is at higher RPMs. *pistons, crankshaft, cams, all move the same still, just different speed depending on RPMs*.  Each piston ignites creating x amount of torque at the given RPM.  Now once the RPM is low enough & cannot create enough torque to move the car in the higher gear how is this actually damaging the engine.  Isn’t the engine really just doing the same thing as it is at idle RPM,  the internals are still all moving the same BUT the only difference at that same low RPM a lot more Air & Fuel is being injected to try & get the car to accelerate at that low RPM.  

This is my understanding of an engine & trying to get some explanation why low RPM in high gear is actually physically damaging / harmful to your engine, I heard someone say something about Oil before? Is oil the final factor? But at the moment with my limited understanding of engines I cannot see why an open full throttle at low RPMs is bad. Please correct / enlighten me.

I think the oil issue is oil starvation at high load and low rpm can cause the engine harm. And the car at idle doing 1400rpm and on load at 1400rpm are 2 very different things

[Cubes]

bah, people worry too much.

Throw it in the highest gear, if you are accelerating enough to labour (vibrate) the motor then select a lower gear.

[geno8r]

I think the oil issue is oil starvation at high load and low rpm can cause the engine harm. And the car at idle doing 1400rpm and on load at 1400rpm are 2 very different things

Ok so lets name what's physically going on differently at 1400 RPM no load & 1400 RPM Full load.

1400 RPM *in Neutral*

Throttle slightly open *around 4%

Minimal fuel being injected

Minimal air being inducted

Exhaust note very quiet *because not much air being passed through engine & out exhaust valves.

*Oil, fill blank here, what’s going on with oil.

1400 RPM *in 5th gear*

Throttle wide open *80 - 100%*

Extra fuel being injected to create a more powerful bang

Extra air being mixed with fuel to create more powerful bang

Exhaust note louder / droned *because a much larger amount of air is being passed through engine out of a still slow 1400 RPM rotating exhaust cam.

*Oil, fill blank here, what’s going on with oil.

I think people are thinking because the engine gets such a low deep / drone exhaust note in that situation that it's gota be bad.

Now I don’t actually know much about how oil lubrication is applied inside an engine but if somebody would like to fill in the blanks for the two examples above I believe it should be the final factor determining whether driving at low RPM in high gear with high load is physically damaging your motor or not, so we're really just about to set this story straight, just need the final oil question answered.

I would have thought the same amount of oil would be being applied at 1400 RPM regardless of load, & that oil is applied at higher amounts in relation to RPM, & if it does apply more oil when the AFM detects more air going in then great. As lanc3 said, “Wouldn't it be common sense to know that forcing movement at a low force wouldn't do much”. Yes… regardless of air / fuel, at such a low RPM how could it be hurting the engine.

[geno8r]

 

Throw it in the highest gear, if you are accelerating enough to labour (vibrate) the motor then select a lower gear.

Yep! the lowest rpm I'll do driving *with my car & engine* is about 1500 RPM... But if I had a real torque’y longer stroke diesel engine it'd probably be 1000 RPM. Hell my dads m8s had an SV300 5.7 V8. You could put that thing in 6th gear, foot off the pedal & it had so much low down torque it would cruze at 80km/h at its idle RPM. & I bet if you dropped the RPM lower than the idle RPM but you had Full throttle you'd still be able to drive along at say 70km/h but in reality you just wouldn’t bother because you’ve got no power left to accelerate, you'd just cruze at 2000 RPM in a lower gear with a slightly open throttle with room to accelerate.

[INASNT]

bah, people worry too much.

 

Throw it in the highest gear, if you are accelerating enough to labour (vibrate) the motor then select a lower gear.

The virbation happens when the engine is in an unbalanced state and for those that work with rotating mechanical equipment know vibration is not a good thing as it causes to stress to all linked components and damage.

geno8r

You will get your answers if you consult a thermo dynamics and fluid dynamics material.

[geno8r]

The virbation happens when the engine is in an unbalanced state and for those that work with rotating mechanical equipment know vibration is not a good thing as it causes to stress to all linked components and damage.

geno8r

You will get your answers if you consult a thermo dynamics and fluid dynamics material.

Yeah I think we've solved this one anyway... *IMHO*

YES YOU CAN drive at low RPM in high gears & not do damage to your engine, BUT once your engine starts vibrating change gears because thats when you will start doing damage.

[INASNT]

High gear, low rpm and the engine is still out of balance abit causing extra wear and tear than normal, so do it all the time and YES it wil cause damage in the long run

[Cubes]

http://theoildrop.server101.com/cgi/ultima...24;t=000641;p=1

http://theoildrop.server101.com/cgi/ultima...c;f=24;t=001148

http://theoildrop.server101.com/cgi/ultima...c;f=24;t=000200

http://theoildrop.server101.com/cgi/ultima...c;f=24;t=000022

http://theoildrop.server101.com/cgi/ultima...c;f=24;t=000621

Should keep you all busy for a while.

[NewKleer]

as some people have stated, i think the issue is more to do with the engine than the gearbox (just they might get the feedback from engine strain thru gearbox)

the main issue is that oil pressure is dependant on rpm - ull get roughly same oil pressure at 1400rpm with no load as u get with load. low load with low oil pressure isnt too much, but low oil pressure with high load and the engine may not be able to get sufficient oil to deal with the higher strain on certain parts of the engine

i think the biggest misconception that leads people to shift early is fuel consumption. what isnt as obvious is that if ur cruising, it doesnt make much difference to fuel consumption whether u are in 5 gear with 40% throttle, or 4th gear with 15% throttle - u have to have roughly the same power to keep u at a given speed. fuel consumption isnt just dependant on revs, but most obviously air flow - u might actually get worse fuel consumption given that the engine isnt at its optimal rpm (highest torque removing boost factors) - ur engine needs a bit more air/throttle to get a given amount of power in a higher gear than a lower gear as it isnt running as efficiently.

[akeenan]

i can't believe so many of you drive in 5th at only 50 or 60kmh!! It just feels wrong!

i usually change at about 3000rpm and only use 5th when I get to 90-100kmh!

if i had to sit in an 80 zone for a while i'd probably whack it in 5th, but if that dropped to a 70 zone I'd have it back in 4th...

AMEN