a new low in fuel economy for my sd33t

[cooter]

[/quote]
no offence but compareing a later model landrover to a bigger old tech nissan is not really fair or accurate.
deisels are built to handle large torque. motors with heavy pistons and heavy cranks do not like high rpm, revving them hard simply wears them out quicker.

as far as encomy goes the more rpm the more fuel your going to use, exspecially on the older style motors which have good low down torque. if anything you should be shifting around the peak torque figure not peak power.[/quote]

jsut to explain my point
have you ever noticed that when you accelerate in a diesel that there is black smoke and then when the revs pick up it dissapears this is because at low rpm you put your foot down and the fuel rack goes to full fuel ther is bugger all force being exerted on the rack from the governor due to its loww rpm so goes to full fuel lots of black smoke now the revs start to climb and the flyweights in the governor start to tr\hrow out due to centrifigal force and begin to apply load on the fuel rack via a spring moving the rack from fuel fuel pos thus reducing fuel and torque next you reach a point where the force applied on the rack from your right hoof and the force applied on the rack from the governor are in an equilibrium
the engine is only useing the fuel it needs to stay at that given rpm
no black smoke

now say u come to a small incline you keep your foot still revs drop slightly all of a sudden black smoke, this is because the force aplied by ur foot is greater than that of the slowing flyweights which allows the rack to move back to the full fuel pos therefore using more fuel once again the revs pick up and the equilibrium is returned

so what i am trying to say is that if you shift at peak torque whilst you get good power you are wasting fuel but if you keep it above peak torque ie higher revs you are efectivley using power not torque therfore rack is at equilibrium fuel is not wasted (black smoke) and the engine will only use what it needs
hope i expained this simply enough
in a petrol engine however say a carbied v8
there is no governor the only thing that controls rpm and fuel ( which in a petrol/ gas engine is directly relative to each other) is your right foot put simply to go faster put your foot down more fuel more revs back of to reduce fuel usage rpm drops so if you are cruising along and you come to a hill u either put your foot down further or shift back a cog whereas a diesel would adjust its fuel automaticaly

i hope this is clear enough and settles some arguments about fuel usage vs driving style

and as for glow plugs they are only a starting aid and will not affect your economy at all just warm the combustion chamber a little to help the initial fire


as you know diesel is ignited by heat from the effect of compressing th air in the cylinder not the glow plugs

Al

[zen]

just sounds shagged to me if it smokes for the first 30mins..mine clears up within seconds...also no black smoke when accelerating..MZ pump though not standard turbo crap pump.much quicker to alter fueling)

deisels are designed to run and be economincal ie effient at low rpm.(and hense max torque at low rpm.) ,if you run them at high rpm all the time expect them to crap out..also petrol engines are ineffiient at low rpm,but effient at high rpm.SO if your driving style is high rpm buy a petrol motor..

cant talk about your sd33 but mine is plenty quick enough.keeps up with traffic no probs,and i change gear at 2000rpm,unless racing when 2500-2800 is more than enough.and i regard 3000rpm as max!!.it is ingood order though.new injectors. 450psi compression...good turbo(boost fron 1000rpm)..straight though exhaust etc..
cruising today at 70mph..2500rpm..just touching throttle..giving 28mpg..thats just over 10l per 100km.goes down if i go any faster and thats using shell diesel fuel

so me.i would give it to diese service centre,get injectors checked and timing checked and compression too..dont get them to do anything just checked over..should not cost much..then go from there according to there report..

oh i still say someone nicking your fuel..

[tweak'e]

jsut to explain my point
have you ever noticed that when you accelerate in a diesel that there is black smoke and then when the revs pick up it dissapears this is because at low rpm you put your foot down and the fuel rack goes to full fuel ther is bugger all force being exerted on the rack from the governor due to its loww rpm so goes to full fuel lots of black smoke now the revs start to climb and the flyweights in the governor start to tr\hrow out due to centrifigal force and begin to apply load on the fuel rack via a spring moving the rack from fuel fuel pos thus reducing fuel and torque next you reach a point where the force applied on the rack from your right hoof and the force applied on the rack from the governor are in an equilibrium
the engine is only useing the fuel it needs to stay at that given rpm
no black smoke

now say u come to a small incline you keep your foot still revs drop slightly all of a sudden black smoke, this is because the force aplied by ur foot is greater than that of the slowing flyweights which allows the rack to move back to the full fuel pos therefore using more fuel once again the revs pick up and the equilibrium is returned



Al

o bollocks! none of my deisels blow smoke at all.

on a turbo deisel, black smoke you you first put your foot on the gas is simply way to much fuel combined with low compression. quite comman exspecially with japimports. the fuel is often a bit to high to give max exaust volume to get the turbo spinning to generate boost as soon as possible. easy fixed, simply adjust max fuel setting down a bit or fix the intake so more air goes into the motor (eg blocked filter or inlet manifold)

these older deisels are basicly a min/max regulator. your foot controls the amount of fuel, if you only give it half throttle you only get half the fuel. otherwise if you went up a hill a half throttle then went full throttle nothing would happen. the throttle simply limits max fuel.

the smoke you discribe is simply your not burning fuel under load which is often caused by lack of compression (and poor injectors) which with a turbo vechile is comman because at part throttle your off the boost so you only have static compression.

good deisels don't blow smoke.

[spannercrab]

Just to throw something else in to the mix here - have you had your pump checked lately? It's possible the advance mechanism is worn (springs are stuffed), or the fuel aneroid is out of whack.

Any way you put it - black smoke is wasted fuel, fuel that wasn't burnt and didn't relinquish it's power in the motor and was still burning on it's way out the zorst. Either due to insufficient air, too much fuel, poorly atomised fuel or incorrect timing.

Usually results in higher EGT's also ... how is your EGT going?

Cooter: black smoke is not a function of low compression, rather insufficient available oxygen to burn the fuel, which is why when the turbo spools up and provides the air, the smoke disappears. The MEP (and compression) on a diesel doesn't really change significantly with the addition of a few psi of boost. The zorst volume increases as revs do and the engine starts to pump more air - the heat is provided from the still-burning diesel going through the turbine - turbines need both to aquire power to spool.

At max advance and max fuel with a free flow exhaust, most diesels will blow some quantity of black smoke as the boost rises to supply the oxygen needed to combust the increasing amounts of fuel being delivered to the pots.

[Patchy]

well i will soon see what your crying bout 84mksd33t might be getting an MQ swb in a couple of days if its too much on fuel i will just acquire diesel off the side of the road (diesel flows like rivers here in wa, much like koala bears are up every lamp post in the eastern states) does the 5sp box bolt straight up to an MQ? i asume they would

[cooter]

Cooter: black smoke is not a function of low compression, rather insufficient available oxygen to burn the fuel, which is why when the turbo spools up and provides the air, the smoke disappears. The MEP (and compression) on a diesel doesn't really change significantly with the addition of a few psi of boost. The zorst volume increases as revs do and the engine starts to pump more air - the heat is provided from the still-burning diesel going through the turbine - turbines need both to aquire power to spool.

At max advance and max fuel with a free flow exhaust, most diesels will blow some quantity of black smoke as the boost rises to supply the oxygen needed to combust the increasing amounts of fuel being delivered to the pots.[/quote]


mate if you read what i wrote you would see i never said that low compression causes black smoke

black smoke is excess fuel which indicates you are trying to overwork the motor it is common sence read what i wrote and think about it it is correct work on bloody oil burners every day i see the evedence of people babying there diesels carbon carbon carbon black smoke means ecess fuel plain and simple turbos put more air in thus offsetting the amount of unburnt fuel
and as for u tweake mate read what u just wrote your desribing a petrol egine not a diesel do some research on diesel governors if you wont take a diesel mechanics word for it
u show me a mechanical diesel that doesent blow smoke
Get tweak'educated

[zen]

mine dont...no black smoke when putting foot down..

BUT it uses vacum/boost controlled fueling..ie mz pump...ie fuels according to vacum boost and revs of course..so does not add extra fuel untill revs or boost increases..hense it fuels correctly all the time..it has NO foot operated control of pump,..so as long as the pump is set up correctly it dont smoke!!

now i dont know why nisaan didnt use the mz pump on the turbo motor as it works so well...no lag at all..infact no manufactor seems to use this type of pump on turbo motors..cost???

[cooter]

there will be a small amount of smoke you may not notice it it just means that yours is running efficiently
for example over here the trukies are going to loose their fuel levy unless their engines meet the benchmark in emmisions ie 10 seconds of black smoke on acceleration no more there will be no mechanical engines at all to meet the criteria

trust me i know as i have been retrofitting 94 on engines to old peices of crap know for 3 years so peoply can get the levy

sorry if i sounded rude but dont like to be told i am wong about something i know i definately am not

[spannercrab]

Whaoh ... sorry cooter ... that comment was directed at tweakz ... not you! My bad ...

Was in response to the "black smoke is made by low compression" comment ...

[cooter]

sorry mate not trying to bite yer head off been in a bad mood just a bit fed up with people tryin to educate me on the workings of a diesel engine i cop it from my boss who knows a little bit of second hand info an trys to make out he knows best i just dont like to see peple led astray as i have been on things i know little about sorry again spanner

[cooter]

sorry mate not trying to bite yer head off been in a bad mood just a bit fed up with people tryin to educate me on the workings of a diesel engine i cop it from my boss who knows a little bit of second hand info an trys to make out he knows best i just dont like to see peple led astray as i have been on things i know little about sorry again spanner

[tweak'e]

thanks for the pics...it helps a bit.

so what i am trying to say is that if you shift at peak torque whilst you get good power you are wasting fuel but if you keep it above peak torque ie higher revs you are efectivley using power not torque therfore rack is at equilibrium fuel is not wasted (black smoke) and the engine will only use what it needs
hope i expained this simply enough

i think your missing my point. the more rpm the fuel you will use to make the same power. as with any motor the higher the rpm the more losses you have.

as far smoke goes i never said it was casued by low compression. i said you first put your foot on the gas is simply way to much fuel combined with low compression. quite comman exspecially with japimports. the fuel is often a bit to high to give max exaust volume to get the turbo spinning to generate boost as soon as possible low compression means fuel dosn't burn well exspecially on the old tech motors. a lot of jap turbo motors are set to over fuel in the off boost position simply so it can get the boost up early as possible. the black smoke is simply fuel the motor isn't burning well, normally lack of air but also lack of commpresion. while a few psi may not make a lot of difference the 6+psi makes a difference. try running a turbo deisel without a turbo, its basicly a atmo with bad rings.

the catch with turbo deisels is when your short shifting its really easy to drop it off boost and thats when your pouring in the fuel, minimal air, burning it poorly due to low compression, hence your fuel usage goes up.

or example over here the trukies are going to loose their fuel levy unless their engines meet the benchmark in emmisions ie 10 seconds of black smoke on acceleration no more there will be no mechanical engines at all to meet the criteria

over here is now illegal to have a vehile that blows smoke for more than 10 secs. it is rare to find a big rig that does. most of the smoky vechiles are half stuffed jap imports. you can tune the off boost smoke and full throttle smoke out of a motor, it just makes them slow.

just a bit fed up with people tryin to educate me on the workings of a diesel engine

get used to it.

it dosn't matter what trade your in someone will always tell you how do to it and believe it or not sometimes you learn something. noone knows everything. no matter what trade or hobby, you are ALWAYS learning something new.

[spannercrab]

not wanting to stir the pot, but:

normally lack of air but also lack of commpresion.

6psi of boost makes very little difference in the overall compression ratio of a turbo diesel engine (or NA).

You still only have -0.02" protutus height regardless of whether it's turbo or not.

The only thing lack of compression in a diesel causes is lack of ignition, which equates to white smoke. Ignition is a function of compression - combustion is a function of available oxygen. The two are entirely different variables.

Once ignition is achieved (through fuel injection into an appropriately compressed & therefore heated air mixture), then the only thing which will result in an incomplete burning of the fuel is a lack of available oxygen.

[MQ080]

What your saying is like tying to get Mitshbishi Mirage economy

My mirage gets filled up every 2.5 weeks and gets 550km per tankfull. Get a second car and leave the MK for weekends!

[tweak'e]

more than welcome to stir the pot

6psi of boost makes very little difference in the overall compression ratio of a turbo diesel engine

i'm not sure of the exact figures, no doubt someone as worked it out but my reasons goes like....

if it made very little difference manafactures wouldn't change the compression ratio for the turbo ver of a motor. simply drive a turbo vechile minus its turbo and see how gutless it is compared to the atmo ver and thats often only 2 difference (ie turbo ver 20:1 atmo 22:1)

compression while not the main cause for black smoke its certianly a factor in burn speed and more importantly burn quality. while it may not cause incompete burning on its own, when you trying to burn too much fuel the quality of burn factor comes into it.

sorry not very good at putting thoughts into words words here.... its one thing to overfuel when you have high compression, but its worse when your overfuelling when its lacking compression. exspecially so with older design motors. at least these new type motors can actually burn fuel well at 16:1.

[tweak'e]

i just did a very rough calulation useing the toyo 2lt motor as a base which has a 20:1 compression. ignoring inlet temp (which will have a BIG impact on this, i'm assuming a perfect intercooler ) effective compresssion goes to 28:1 with 6psi of boost. i'll redo it once i work out how to add temps into it.

[cooter]

that is all well in good in theory but what you are not thinking about is the fact that the only reason you run a turbo is to make the engine more volumetric efficient Compression ratio eg 20:1 is what the engine is rated at but considering a naturally aspirated engine is only roughly 60 % volumetric efficient you add a turbo to force more air into the combustion chamber thus making the VE percentage rise closer to the 100 % mark

to make sence of that giberish ve is the ratio of air sucked or forced into combustion chaber and swept volume
so whilst boost will increase an engines compression slightly it will never be over a manufacturers specs

[tweak'e]

not to sure what your driving at here.... of course it never goes over manufacturers specs, the manufacturer built it !

VE dosn't really matter that much. the motor is filled with gas even if it isn't air.

the whole point i was trying to make is the turbo/supercharge rule of thumb (reguardless of fuel) is "the more boost you run the lower the static compression needs to be" the problem of course is with any fuel the more compression the better it burns, so when you lower compression the burn gets poorer. thats the catch 22 of turbo motors, which is why (as well as starting problems) no manafacture has made high boost turbo deisels untill recently. the older motors simply do not burn deisel well at low compression.

[zen]

what do you class as high boost??
(ie land rover 200/300tdi has run 15psi since 1988..18yrs..)

[tweak'e]

i don't know land rovers, a bit of a rarity around here. a quick google showed 19.5:1 compression and fairly low HP. if they are running 15psi its not for the amount of air. according to a few sites it list those motors as early to mid 90's not late 80's. i've no doubt you could run them at 15psi, plenty of toyo of that age can run at that easy enough.

it really hasn't been intill the 2000 that compression has dropped (eg 15:1) and high boost used. someone mentioned nissian was useing 20+psi ??. hopefully i'll get a boost gauge fitted and see.

[zen]

well my sd33 is running 16 happily..