Question for the clever people

[muddymatt]

Hi,

This was asked to me and I didn't know the answer so I thought I would pass it to the forum....

When driving up a big long hill is it better for the engine to either floor it in fifth at the bottom and keep the pedal flat down only changing down when you have to as you are either about to drop off the turbo if you are in a turbo D or the engine is about to lug if it's a petrol

OR

Drop it to 4th at the beginning of the hill and use part throttle but much higher revs.

I know there are literally loads of variables such as engine type, condition etc but we are only talking hypotheticals.

Also which will use less fuel?

Cheers,

Matt

[mudlva]

interesting question i reckon that using more revs with less throttle is better then trying to heavy at low down revs. sopose thinking that if the foot is buryied two icnhs below the floor boards (so to speak) then this would use more fuel than higher revs and using the foot peddle properly
just my thoughts
cheers

[tweake]

use 5th as much as you can, BUT you must change down at the right time. that of course vaires depending on the vechile, you want to keep it moving and not drop it off boost or cam. no point droppping the revs and speed right down in 5th then changing and accerating in 4th, that will chew even more gas.

more revs but less throttle vers full throttle but low revs? depends on motor. full throttle low rpm is better but some vechiles overfuel badly so with those its better to back off the throttle and use the revs to maintain power.

[2MEKE]

Using option 1 in a turbo diesel will send the engine temps up rather quickly

[Bulletproof]

Hi,

This was asked to me and I didn't know the answer so I thought I would pass it to the forum....

When driving up a big long hill is it better for the engine to either floor it in fifth at the bottom and keep the pedal flat down only changing down when you have to as you are either about to drop off the turbo if you are in a turbo D or the engine is about to lug if it's a petrol

OR

Drop it to 4th at the beginning of the hill and use part throttle but much higher revs.

I know there are literally loads of variables such as engine type, condition etc but we are only talking hypotheticals.

Also which will use less fuel?

Cheers,

Matt

A Good rule of thumb is not to go below the max torque revs of the motor. So if your engine develops max torque at 2200rpm change down as soon as you drop back to that rev.

Richard

[tweake]

Using option 1 in a turbo diesel will send the engine temps up rather quickly

thats only a problem if your motor is prone to overheating. will any decent motor thats not a problem.

[wopass]

use 5th as much as you can, full throttle low rpm is better

not for your engine it isnt, your main bearings will get hammered the shit out of and fail prematurely

pick your gear before you need it on a hill as if you have to change down half way up you will loose your momentum and be fighting to get it back again.

[Steve_t647]

I agree you will know where the engine produces power and where it starts to struggle the trick is to prevent the engine working hardin mine (petrol) as soon as it gets near 3k I will chop down and keep up the road speed the more momentum you keep with you the better your economy

[Sadam_Husain]

A Good rule of thumb is not to go below the max torque revs of the motor. So if your engine develops max torque at 2200rpm change down as soon as you drop back to that rev.

Richard

Thats Right on the button

But change down before it drops off coz you'll lose momentum between the gear changes

[Pedro]

Hi,

This was asked to me and I didn't know the answer so I thought I would pass it to the forum....

When driving up a big long hill is it better for the engine to either floor it in fifth at the bottom and keep the pedal flat down only changing down when you have to as you are either about to drop off the turbo if you are in a turbo D or the engine is about to lug if it's a petrol

OR

Drop it to 4th at the beginning of the hill and use part throttle but much higher revs.

I know there are literally loads of variables such as engine type, condition etc but we are only talking hypotheticals.

Also which will use less fuel?


if you have to change gear then the motor up front aint big enough!!!!

Cheers,

Matt

[SMOKEY]

It's not often I will criticise but people shouldn't give advice unless they know what they are talking about . I have been in the Automotive industry for over 40yrs, most of this time as a Mechanic, also heavy truck driving and machinery operator. All I will say is to use the gear box matched to the RPM . Talk to drivers that have an Exhaust Temperature (pyrometer) gauge fitted they will tell you the temperatures that can be achieved with different driving technics, and not using your gear box will send the temperature over the safe driving range with in a very short space and time.

FITZY.

[tweake]

use 5th as much as you can, full throttle low rpm is better

not for your engine it isnt, your main bearings will get hammered the shit out of and fail prematurely

pick your gear before you need it on a hill as if you have to change down half way up you will loose your momentum and be fighting to get it back again.

its fine on your motor unless its a thrashed out piece of crap or its highly modded (ie over fuels).
when i mean low rpm, thats typically still above max torque with most diesels.

chopping down a gear at the bottom of the hill before the clime will often means your sitting on the red line, that will chew fuel like crazy. much more efficient to keep in the higher gear and cruise up the hill.

of course all this will vary depending on weight/motor etc. provided your not going to be crawling up the hill, you should easily keep within efficient rpm range of the motor. if your hauling large weight or have a slow piece of crap you have to bite the bullet and go full noise early as possible, change down as soon as possible to get max power and keep that momentum going.
also will vary with gearing, if you have 2000rpm difference between gears your change points are going to be a whole lot different than if you only had 500rpm difference.

at the end of the day if you can get away with going up hill in higher gear it will be more economical than sitting at high rpm in a lower gear.

[muddymatt]

Thanks for all the inputs guys. The general consensus seems to be that as long as you are not lugging the motor or are in the turbos operating zone there is nothing to be gained by changing down earlier even if you are flat down from the base of the hill untill that point???

For example my Disco TDi will go up a very long local SH1 hill in 5th if I hit the start of the slope at 120K (sorry officer) and keep the foot planted till the top. Speed at the summit is about 80K and the motor is still just on 2000 rpm which is in the turbo but only just - 1900 rpm and it drops off.

Loaded up with gear or too slow at the start and you have to change down, so should I go for fourth at the bottom?

[tweake]

It's not often I will criticise but people shouldn't give advice unless they know what they are talking about . I have been in the Automotive industry for over 40yrs, most of this time as a Mechanic, also heavy truck driving and machinery operator. All I will say is to use the gear box matched to the RPM . Talk to drivers that have an Exhaust Temperature (pyrometer) gauge fitted they will tell you the temperatures that can be achieved with different driving technics, and not using your gear box will send the temperature over the safe driving range with in a very short space and time.

FITZY.

please by all means criticise away, how else am i going to learn something new

i got to ask.... why is the motor even capable of getting over max EGT's ?
running high but safe EGT's is not going to hurt.

the thread here is on what econimical, not whats going to make it last another million miles.

[tweake]

Thanks for all the inputs guys. The general consensus seems to be that as long as you are not lugging the motor or are in the turbos operating zone there is nothing to be gained by changing down earlier even if you are flat down from the base of the hill untill that point???

For example my Disco TDi will go up a very long local SH1 hill in 5th if I hit the start of the slope at 120K (sorry officer) and keep the foot planted till the top. Speed at the summit is about 80K and the motor is still just on 2000 rpm which is in the turbo but only just - 1900 rpm and it drops off.

Loaded up with gear or too slow at the start and you have to change down, so should I go for fourth at the bottom?

depends entirely on what speed your hitting the bottom at and what gear spacing you have. i suspect you will probably to fast to drop back to 4th at the bottom.
i normally go up in 5th and change about 2000 to 4th which gives 3000 rpm which is just under max power in the ute. that will do most hills, smaller hills 1500-2500 will do. if i changed at the bottom i would be doing 4000rpm and well over max power mark. generally that will drink fuel like crazy, usually only do that if its fully loaded and need to keep in the power band 3000-3500. not efficient but beats crawling up the hill in 2nd.

[tallsam66]

Throw away the manual & get an auto..it will just do its own thing

[fred flintstone]

It's not often I will criticise but people shouldn't give advice unless they know what they are talking about . I have been in the Automotive industry for over 40yrs, most of this time as a Mechanic, also heavy truck driving and machinery operator. All I will say is to use the gear box matched to the RPM . Talk to drivers that have an Exhaust Temperature (pyrometer) gauge fitted they will tell you the temperatures that can be achieved with different driving technics, and not using your gear box will send the temperature over the safe driving range with in a very short space and time.

FITZY.

please by all means criticise away, how else am i going to learn something new

i got to ask.... why is the motor even capable of getting over max EGT's ?
running high but safe EGT's is not going to hurt.

the thread here is on what econimical, not whats going to make it last another million miles.

but the making it last another million ks, is PART of the economics...
I agree with Fitzy, I drive a 18 speed at work, and you can do it the hard way, or the easy way,
both will get ya there, but one is easier, therefore cheaper

[wjw]

Throw away the manual & get an auto..it will just do its own thing

Not true, with an auto you need to learn throttle control and blip the throttle so it changes down before it starts labouring. On a long steep winding hill its not as easy as you would think... I've been practisicing driving upto Mt Hutt, just about got it right now. So the truck, doesn't get hot, doesn't labour, and doesn't take me three years to get up. It's definitely easier in a diesel where the torque is down low.

[tweake]

Throw away the manual & get an auto..it will just do its own thing

and autos suck even more gas than manuals so thats a backwould step.



if i can put it simply with my limited writing skills (read none!) ......

keeping it in higher gears as long as possible will be more economic. whats practical will vary depending on vehicle, load and conditions.
can i get it any vaguer ?

work out what suits you.

on a side note seeing as there is a few truckies here.........whats with the truck drivers at the moment ? seeing a lot that are driving slow to save fuel but others speeding and pushing vechiles off the road.
there is a lot of traffic thats driving slower these days and that seams to be holding up certain people who are simply smashing their way through trafffic. seeing a lot more trucks pushing trucks out of the way as well.

[skid]

my last 2 cruisers were both diesel turbos, 1st a 13bt(BJ74) and now the 1hdt(VX,80 series) and with both of them I have always played between 2000-3000rpm.

that is, if it gets to 3000, then most times I will change up and if it gets down to 2000, then its time to change down.

the one and only time I did not do this was when I was looking in my mirror to see how much smoke I was producing out the exhaust and also showing a boy racer hiace van a thing or two (at 4200rpm) about power whilst I was towing my 40 on the trailer behind me, it was up a big hill in the desert road and they were trying to overtake me and after a short time I finally looked at my temp gauge to see it had gone nearly off the clock, so I immediately backed off and the temp came down and then I stopped at the top of the hill to let it cool down and smack myself on the hand for being so stupid.

so thrashing the hell out of your diesel turbo in my books would be a dumb idea, especially if you are towing.

my 2c

Cheers

SKID

[sig]

if you want to burn of the boyracers skid you need marks tourag.150kph up the maungawekas with his forty on the trailer behind him watching the expressions on the wrx owners face as he cruised past him

[skid]

if you want to burn of the boyracers skid you need marks tourag.150kph up the maungawekas with his forty on the trailer behind him watching the expressions on the wrx owners face as he cruised past him

not to mention the poor 4wder in his 80 who had the displeasure of having mark pull up beside him towing his 40 as well and wave, before accelerating away again.

yes it would be nice to have 750nm of torque, wouldn't it

[wjw]

I stopped at the top of the hill to let it cool down and smack myself on the hand for being so stupid.

You should have let it cruise down the hill, would have cooled it quicker...

[skid]

I stopped at the top of the hill to let it cool down and smack myself on the hand for being so stupid.

You should have let it cruise down the hill, would have cooled it quicker...

not sure if you know the desert rd, but at the top of this hill is the 3 sisters, which consist of 3 25kph winding hairpin corners that are hilly. I really did need to let it cool down before I went any further.

[cool__bananas]

if you want to burn of the boyracers skid you need marks tourag.150kph up the maungawekas with his forty on the trailer behind him watching the expressions on the wrx owners face as he cruised past him

didnt crusty say that marks speedo goes up faster than the hiaces rev counter?

[tpft]

labouring a gear high, with your foot flat is nearly chewing as much fuel as a gear lower and reving.
I,d think the extra fuel drawn into the engine at a lower revs would have a cooling effect though, even though the airflow threw the cooling system is less.

heat equals power, a engine is just a big heat exchanger.
quicker u get to the top,or the heavier u are, the more heat u have made and the more fuel u have used.

if u were in first and kept revs down and crawled to top it would be best for cooling system heat and fuel consumption.

temp is most important, if engine temp gets up that could cost a lot more then a few cents of fuel............

p.s clever people drive hybrids don,t they????

[Bulletproof]

Throw away the manual & get an auto..it will just do its own thing

and autos suck even more gas than manuals so thats a backwould step.



if i can put it simply with my limited writing skills (read none!) ......

keeping it in higher gears as long as possible will be more economic. whats practical will vary depending on vehicle, load and conditions.
can i get it any vaguer ?

work out what suit

I agree with Fitzy and what you say is bad advice and could cause someone to cook there motor

As Fitzy said if you talk to people with a pyrometer you would get a shock how quickly the temperature goes up by holding a high gear. Within 1 min the temperature can move from 400-700 degrees celcius. This the temperature that iron glows red hot at.
This is nothing to do with what the temperature guage says which is water temperature and if this is up you may already have done damage
You made the statement that this is only if your motor is stuffed. This is a load of rubbish as it applies just as much to a new motor.
Regarding economy holding a high gear does not save fuel. All you are doing is increasing the torque and strain on everything.
If you dont have a pyrometer .I stick to the rule of changeing down around the max torque line of your motor.

Richard

[BIGK]

i didint notice any truckers on here TWEAKE?(and please define a truck?)
the auto/manual economy theory in a hvy truck buddy is crap!autos use less fuel!
many dont drive to the rd nor their load which is why you will always see many on their side...get used to it

750nm you aint even half way yet

[KiwiBacon]

Your engine always uses less fuel at higher load and lower rpm.
Diesels are most efficient around the rpm that gives them max torque and at almost maximum load. Petrols are most efficient at around 2/3 their max torque rpm and again at almost maximum load.

Changing down early uses more fuel.
Higher rpm uses more fuel.
Your diesel engine is most efficient with the highest load you can put on it without blowing smoke.
Running below your maximum torque uses less fuel than running above it.
Your engine big end bearings and EGT's are only a concern if your engine is either worn out or has been tweaked.
Autos always use more fuel, why do you think they need a transmission cooler?
Yes Tweak'e is correct.

I wrote this on outerlimits the other week, including graphs of engine fuel consumption (petrol and turbo-diesel) and worked examples.
Seventh post down.
http://www.outerlimits4x4.com/sutra1403136.php#1403136

[nzhunter]

the auto/manual economy theory in a hvy truck buddy is crap!autos use less fuel!

Umm then again it depends what sort of auto box it has even, for example the big red waste management hino trucks with an allison auto box use alot more fuel than the ones that are manual even if its exactly the same truck. But the new macks and stuff with an eaton fuller auto shift box which is a manual gearbox (has a clutch even) is controlled electronically through the ecu and a series of solenoids to make it an auto, and these use alot less gas than a manual of the equivalent.

750nm you aint even half way yet

try 2250nm of torque!!