ULTIMATE Petrol vs Diesel thread - Comparisons





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  1. #1
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    Default ULTIMATE Petrol vs Diesel thread - Comparisons

    This thread has it's origins here:
    http://www.4x4community.co.za/forum/...ad.php?t=79935

    Then continued here in order to gather data:
    http://www.4x4community.co.za/forum/...ad.php?t=80136

    Introduction
    This thread has it's origins in the countless other Petrol vs Diesel threads, and claims made in these threads, about the advantages of turbo diesel engines.
    1) It is claimed that the high torque at low rpm, that is characteristic of turbo diesels, is directly translated into performance.
    2) Also that the higher maximum torque values of turbo diesels, compared to naturally aspirated petrol engines, are also an indication of performance.
    3) That the higher torque values at low rpm hold an advantage off road.
    4) That diesels are cheaper to run, due to their lower fuel consumption.

    Aim
    It is my aim to show that:
    5) A petrol engined variant, in the same family and price group, will out perform it's diesel sister-model in every way.
    6) See above
    7) Traction limits are reached well before high torque values at low rpm have any influence.
    8 ) The perceived saving in fuel, when buying a turbo diesel, is only a partial picture. I will highlight some of the other factors to consider, and include some examples.

    Transparency
    The Excel sheets used to automate the calculations will be made available for each model group. I will also include source material used for each model where possible. I tried to not be involved with the data gathering, but I did have to source some of the data myself. Where possible I will either provide links to the source, or the relevant document itself.

    Methodology
    As Apoc and myself discussed in this thread:
    http://www.4x4community.co.za/forum/...ad.php?t=79935
    the method will be simple.

    Torque on the wheel driving axle will be calculated in simulated, wide open throttle runs from various speeds to various speeds.
    In cases where the petrol and diesel variants run different tyre sizes, the actual force exerted across the loaded radius of the tyre will be calculated.
    This is done, because we know that torque (or rather the force that is a component of Torque as Force.Distance) at the wheels is the direct driver of acceleration, as described by F=m.a
    In addition, the rpm of the wheel drive shaft will be checked, or road speed rather. This is because, in addition to torque on the wheel drive shaft, that shaft will also have to maintain minimum speeds in order to keep up with the comparison vehicle. Huge torque on the wheel drive shaft means nothing, if the shaft's speed is low. The acceleration will be massive, but the vehicle will be unable to attain speed, because the speed is low.
    This is also why the same vehicle variants have to be used. Since the aerodynamic drag and other forces acting on the vehicles will be pretty much the same, it will be down to the engine and drivetrain only, to provide performance. Differences in mass can easily be incorporated in the calculation if they are significant.

    What I want the reader to learn
    I hope that this writing will provide a clearer picture of what torque and power are.
    I want the reader to understand that engine torque, no matter how big the numbers, does not mean anything if you do not know what the drivetrain does with it.
    I want the reader to understand that the amount of traction you have offroad is much more important than the amount of torque your engine can deliver.
    I want the reader to understand what a stall torque ratio is, when looking at an automatic transmission.

    Additional Notes
    This article and calculations are submitted for peer review, by you, my peers.
    I encourage everyone to look at the calculations, and understand them. Understand why each step is done.
    And obviously, question, and be critical of them.
    I have to stress, that these calcs are based on, "all things being equal", which is why specifically the models and variants have to be the same. The more they are the same, the more accurate the result. But the numbers themselves are subject to error, because things like drivetrain losses are not accounted for. But it is assumed that these losses will be very close to the same, and as such, though the figures will change, they will all change, and the conclusions will remain the same.

    I encourage all new readers to catch up with the story, by reading the 2 posts noted at the beginning of this post.

    Tyre Size Calculator used: http://www.miata.net/garage/tirecalc.html
    Last edited by RedLineR; 2011/03/29 at 10:04 AM.
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    Default Mitsubishi

    Updated with new xls file.

    First off, on the first sheet I list the 3 Triton models that were requested for comparison.
    But, as can be seen the 2.5 Di-D is much cheaper than both the 3.2Di-D and 3.5L MPi.
    For this reason, I do not consider the 2.5 as an option that a buyer would consider if shopping in the R365k range.
    The comparison is thus between the 3.2Di-D and 3.5MPi, with the 3.5 being the cheaper of the two.
    I had figures at hand for the gear and diff ratios of the manual transmission versions.

    The attached sheet so far, does a high range only comparison, based on available figures.

    The first frame on the first sheet named "Comparison":

    Here the basic specs are laid out as found in the sales brochure.
    Actual Torque at Maximum Power is calculated.
    Actual Power at Maximum Torque is calculated.
    These 2 calculations serve only as a control, to verify that the torque curve supplied by the manufacturer has some semblence to reality.
    It can be seen that the 2 models use the exact same gearbox, the petrol is equipped with a higher ratio diff. The effects of this will become clear in the wheel torque -, and speed calculations.
    The tyre size is as specified in the brochure.
    The wheel circumference is theoretical, and is not calculated by myself. I used a tyre size calculator. The link is in the first post.

    Next up are the Sheets named "Diesel" and "Petrol":
    In the first frame the torque curve is numerated at rpm intervals.
    The kW is again calculated as a control only. This helps to confirm accuracy of the torque figure read from the graph.
    Note that the rpm intervals are not constant. This was a neccesary evil, to be able to display the rpm at maximum power for each engine. The maximum torque rpm lies on the default rpm intervals.
    The diesel in this case has a row added at 3750rpm, and the petrol has a row added at 4750rpm.

    In the next 6 frames, wheel torque (or torque at the wheel) is calculated for each rpm interval, for each gear.
    The formula is straight forward:
    It takes the engine torque at that rpm, multiplied by the ratio of the specific gear, multiplied by the transfercase ratio, multiplied by the diff ratio. All these figures are from the brochures and graphs.
    This is done for all rpms and all gears, for both engines.

    Then lastly we return to the first sheet named "Comparison":
    Here I list the wheel torque at corresponding rpms for both engines, and each frame covers a gear.
    A theoretical road speed is calculated using the tyre circumference from the link in post #1.
    Using the Engine rpm, divided by the gear ratio, divided by the transfercase ratio, divided by the diff ratio, gives us the rpm of the wheel/drive shaft. This, multiplied by the tyre circumference in millimeters gives us mm/minute. Take that times 60, gives us mm/h. And that divided by 1000000, gives us km/h.

    Notes on the comparison:

    We can see that at 1000rpm, the turbo charger on the diesel engine is not providing enough boost, and the wheel torque figures are very close to that of the petrol.
    At 1500rpm, the turbo charger seems to be providing sufficient boost to give a good performance increase. The slightly higher diff ratio of the petrol is not sufficient to overcome this.
    But this changes again very rapidly somewhere between 3000 and 3500rpm, where the petrol then overtakes the turbo diesel in terms of torque at the wheel.
    When the turbo diesel approaches it's redline, the petrol engine is making the same amount of torque more, than the diesel was making over the petrol at 2000rpm.

    At this point the diesel has to shift, and our focus moves to the 2nd gear table for the diesel.
    The diesel is doing about 32km/h at it's redline in 1st gear.
    Thus is will be sitting at around 2000rpm and 30km/h in 2nd gear when the shift is complete.
    Now at 30km/h in 2nd gear the actual wheel torque is only 3277Nm on the diesel. The petrol is still in 1st at this point and is pulling 5564Nm at the wheels.
    The reader can follow the blue text through the gear shifts.

    Additional Notes:
    1) Wheel Torque, or Torque at the wheels here is a term I use in a colloquial sense, in that I refer to it almost as the output on a single shaft, while it will be split 50/50 on an open diff. The figure can simply be divided by 2 for a rear wheel drive only, open differential drive train, on tarmac.
    2) I do not have the maximum speed figures available, and could not find them in the brochures, hence the calcs are done to redline in every gear.
    3) I would like to add some more calculations in order to actually calculate a theoretical top speed based on all applicable variables. It would just be nice to see how close it is to actuals.
    4) I would like to add a low-range section, though the overall picture would not change, since the low range ratios are also exactly the same on both models. Just for the sake of being complete.
    5) I would like to obtain fuel consumption figures for both these vehicles in order to calculate how many km are needed to justify the additional cost of the diesel, assuming that the vehicles are under a maintenance plan, which negates any maintenance costs.
    6) Price link: http://www.mitsubishi-motors.co.za/M...t1/default.asp
    7) Tech Spec Brochure link: http://www.mitsubishi-motors.co.za/M...ochure2010.pdf

    Conclusions:
    1) From the data it can now be seen, that the turbo diesel has an acceleration advantage over the petrol from 8-28km/h. From 0-8km/h they are pretty evenly matched, due to the turbo not spinning fast enough yet to provide sufficient boost. From 28km/h onwards, it's pretty much a one horse race through the remaining gears, because the petrol can remain in the lower gears for longer and thus benefit from the reduction ratio of that gear, while the turbo diesel has to shift, and lose gear ratio advantage.

    2) It should also be noted that the petrol actually makes more torque at the wheels in large parts of it's own rev range, and even in the overlapping rev range.

    3) From the Comparison table, the reader can now also pick any speed to accelerate from, and compare the wheel torque on both vehicles in their suitable gears, and the petrol will again outperform the diesel almost every single time, for given ranges.

    4) What the figures do also show is drivability at low/medium rpm (1500-3000rpm) for the turbo diesel.

    5) Maintaining a constant speed in a gear that leaves the engine running between 1500-3000rpm is done with less driver effort in the turbo diesel. Where the turbo diesel might be able to maintain a constant speed up a hill, as the accelerator is slowly depressed all the way to full throttle to maintain constant speed. The petrol could require a downshift if the hill is sufficiently steep to overcome the available torque at the wheels.
    This is most clearly illustrated on the last graph, where the diesel has better gradient of ability than the petrol at mid-range rpms.

    6) At the very low rpm ranges, that's used during obstacle negociation, the petrol and diesel are equally matched, because the turbo diesel is virtually naturally aspirated at those very low rpm ranges (Idle - 1500rpm).

    Summary:
    The Conclusions (listed above) address most of the 8 Introduction and Aim points as listed in post #1.
    Additional data like fuel consumption is required to address, the missed points, and further objectives.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by RedLineR; 2011/05/02 at 12:01 PM.
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    Default Nissan NP300

    A big thank you to BoyScout, who researched all the figures for this comparison.
    http://www.4x4community.co.za/forum/...&postcount=291

    First off, on the first sheet I list the 2 Nissan NP300 Double Cab 4x2 models that were requested for comparison. I could not use the 4x4 versions since there is not a 4x4 diesel Double Cab available, contrary to popular opinion.

    The comparison is between the 2.5DCi and 2.4i, with the 2.4i being the cheaper of the two.
    Please refer to other comparisons for an explanation of how the sheet is filled in, and what each figure means. Also feel free to ask for a more detailed explanation on figures and formulas, and reasons for their compilation.

    Notes on the comparison:

    This was a very interesting and very close comparison. It is also the first comparison done where the turbo diesel actually has a larger displacement than it's sister petrol model.
    The diesel is about R24 000 more expensive than the petrol, but again, the lack of consumption figures means we cannot calculate how many km that translates to. I took a stab at guessing the consumptions, feel free to change this if data becomes available.

    This is pretty much a one horse race.
    The petrol accelerates faster than the diesel, and just keeps going. The diesel is never any competition for the petrol.
    Here it's the additional weight that the diesel carries around that really kills it.

    This can simply be proven by changing the weight of the petrol vehicle to be the same as the diesel. Then performance becomes pretty much the same with the petrol and diesel being just about equal all the way to almost 160km/h.
    But, the diesel has to carry it's additional 130kg. A drawback of a heavy diesel engine.

    The diesel does hold a small advantage in 4th gear gradient of ability, and this is dimished in 5th.

    Additional Notes:
    1) Wheel Torque, or Torque at the wheels here is a term I use in a colloquial sense, in that I refer to it almost as the output on a single shaft, while it will be split 50/50 on an open diff. The figure can simply be divided by 2 for a rear wheel drive only, open differential drive train, on tarmac.
    2) I do not have the maximum speed figures available, and could not find them in the brochures, hence the calcs are done to redline in every gear.
    3) I would like to add a low-range section, though the overall picture would not change, since the low range ratios are also exactly the same on both models. Just for the sake of being complete.
    4) I would like to obtain fuel consumption figures for both these vehicles in order to calculate how many km are needed to justify the additional cost of the diesel, assuming that the vehicles are under a maintenance plan, which negates any maintenance costs.

    Conclusions:
    1) From the data it can now be seen, that the larger displacement turbo diesel has no performance advantage over is smaller, naturally aspirated petrol sister. Not in acceleration, and not in top speed.

    2) It should also be noted that the petrol actually makes more torque at the wheels across most all speeds and rev ranges.

    3) From the Comparison table, the reader can now also pick any speed to accelerate from, and compare the wheel torque on both vehicles in their suitable gears, and the petrol will again outperform the diesel every single time, for given ranges.

    4) What the figures do also show is a drivibility advantage durin in-gear acceleration. This can either be interpreted as ability to cruise up a hill in a fixed gear, or over-taking in a fixed gear.

    5) Maintaining a constant speed in a gear that leaves the engine running between 2000-3000rpm is done with less driver effort in the turbo diesel. Where the turbo diesel might be able to maintain a constant speed up a hill, as the accelerator is slowly depressed all the way to full throttle to maintain constant speed. The petrol could require a downshift if the hill is sufficiently steep to overcome the available torque at the wheels.

    6) At the very low rpm ranges, that's used during obstacle negociation, the petrol and diesel are equally matched, because the turbo diesel is virtually naturally aspirated at those very low rpm ranges (Idle - 1500rpm).

    7) The turbo diesel does cost more, and the owner will have to drive it for approximately 60 000km, before a saving can be had. This will change depending on the actual fuel consumption achieved, and prevailing fuel prices.

    Summary:
    The Conclusions (listed above) address most of the 8 Introduction and Aim points as listed in post #1.
    Additional data like fuel consumption is required to address, the missed points, and further objectives.
    Attached Files Attached Files
    Last edited by RedLineR; 2011/05/02 at 01:46 PM.
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    Default

    Reserved - Jeep
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    2009 Suzuki Grand Vitara 3.2i V6 Auto
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    Default

    Reserved - BMW
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    Default Toyota Fortuner

    First off, on the first sheet I list the 2 Fortuner (Auto) models that were requested for comparison.
    The comparison is thus between the 3.0D4-D and 4.0 V6, with the 3.0 being the cheaper of the two.
    I had figures at hand for the gear and diff ratios of the auto transmission versions. I did not have the torque ratios for the torque converter unfortunately. Once I've done a bit more research I can include this as well, even if just generic.

    The attached sheet so far, does a high range only comparison, based on available figures.

    The first frame on the first sheet named "Comparison":

    Here the basic specs are laid out as found in the sales brochure.
    Actual Torque at Maximum Power is calculated.
    Actual Power at Maximum Torque is calculated.
    These 2 calculations serve only as a control, to verify that the torque curve supplied by the manufacturer has some semblence to reality.
    It can be seen that the 2 models use different gearboxes, but the same transfercase and diff.
    The tyre size is as per info supplied by a member.
    The wheel circumference is theoretical, and is not calculated by myself. I used a tyre size calculator. The link is in the first post.

    Next up are the Sheets named "Diesel" and "Petrol":
    In the first frame the torque curve is numerated at rpm intervals.
    The kW is again calculated as a control only. This helps to confirm accuracy of the torque figure read from the graph.
    Note that the rpm intervals are not constant. This was a neccesary evil, to be able to display the rpm at maximum power and torque for each engine.
    This interval inconsistency is carried to all tables to ensure the comparison remains valid.

    In the next 6 frames, wheel torque (or torque at the wheel) is calculated for each rpm interval, for each gear.
    The formula is straight forward:
    It takes the engine torque at that rpm, multiplied by the ratio of the specific gear, multiplied by the transfercase ratio, multiplied by the diff ratio. All these figures are from the brochures and graphs.
    This is done for all rpms and all gears, for both engines.

    Then lastly we return to the first sheet named "Comparison":
    Here I list the wheel torque at corresponding rpms for both engines, and each frame covers a gear.
    A theoretical road speed is calculated using the tyre circumference from the link in post #1.
    Using the Engine rpm, divided by the gear ratio, divided by the transfercase ratio, divided by the diff ratio, gives us the rpm of the wheel/drive shaft. This, multiplied by the tyre circumference in millimeters gives us mm/minute. Take that times 60, gives us mm/h. And that divided by 1000000, gives us km/h.

    Notes on the comparison:

    This is pretty much a one horse race throughout. The petrol generates more torque at the wheel through all speed and rpm ranges.

    This is because it's fitted with a 5spd Auto box instead of the 4spd found on the D4-D. Also, the 4.0 V6 is superior in terms of torque and power. These facts virtually renders the comparison invalid.

    The characteristic of the turbo diesel, is that the torque drops of sharply after it's peak. This is detrimental to performance as can be seen.

    The D4-D could come back with the addition of fuel consumption and running costs.

    Additional Notes:
    1) Wheel Torque, or Torque at the wheels here is a term I use in a colloquial sense, in that I refer to it almost as the output on a single shaft, while it will be split 50/50 on an open diff. The figure can simply be divided by 2 for a rear wheel drive only, open differential drive train, on tarmac.
    2) I would like to add some more calculations in order to actually calculate a theoretical top speed based on all applicable variables. It would just be nice to see how close it is to actuals.
    3) I would like to add a low-range section, though the overall picture would not change, since the low range ratios are also exactly the same on both models. Just for the sake of being complete.
    4) Price link: www.toyota.co.za
    5) Tech Specs: Supplied by CoenraadB and Uys. Thanks guys!

    Conclusions:
    1) From the data it can now be seen, that the turbo diesel has no performance advantage over the petrol anywhere.
    2) It should also be noted that the not even in the low rev ranges does the D4-D come close to the petrol.
    3) From the Comparison table, the reader can now also pick any speed to accelerate from, and compare the wheel torque on both vehicles in their suitable gears, and the petrol will again outperform the diesel every single time, for any given ranges.
    4) The D4-D suffers greatly due to it's 4spd auto gearbox, and it could be one of the reasons that it's cheaper than it's petrol sister.

    Summary:
    The Conclusions (listed above) address most of the 8 Introduction and Aim points as listed in post #1.
    Additional data like fuel consumption is required to address, the missed points, and further objectives.
    The petrol with it's higher performance figures and better choice of gearbox, renders this comarison virtually invalid. It's not as close as the Tritons with the same gearbox, but different diff ratios.
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    Last edited by RedLineR; 2011/05/02 at 10:46 AM.
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    Default Mitsubishi Pajero

    First off, on the first sheet I list the 2 Pajero models that were requested for comparison.
    The comparison is between the 3.2Di-D (CDI) and 3.8L V6, with the 3.8 being the cheaper of the two.
    I had figures at hand for the gear and diff ratios of the auto transmission versions.
    NOTE: All these figures are from Mitsubishi Australia. Please confirm, as a matter of urgency, that these vehicles are identical to the SA version!

    The attached sheet so far, does a high range only comparison, based on available figures. But because the low range ratios are the same, the picture will remain exactly the same. All the wheel torque figures can just be multiplied by 1.9, and all the speeds divided by 1.9.

    The first frame on the first sheet named "Comparison":

    Here the basic specs are laid out as found in the sales brochure.
    Actual Torque at Maximum Power is calculated.
    Actual Power at Maximum Torque is calculated.
    These 2 calculations serve only as a control, to verify that the torque curve supplied by the manufacturer has some semblence to reality.
    It can be seen that the 2 models do not use the same gearbox or diff.
    The tyre size is as specified in the brochure.
    The wheel circumference is theoretical, and is not calculated by myself. I used a tyre size calculator. The link is in the first post.

    Next up are the Sheets named "Diesel" and "Petrol":
    In the first frame the torque curve is numerated at rpm intervals.
    The kW is again calculated as a control only. This helps to confirm accuracy of the torque figure read from the graph.
    Note that the rpm intervals are not constant. This was a neccesary evil, to be able to display the rpm at maximum power and torque for each engine. This inconsistent rpm interval is carried across all tables, in order to enable direct comparison.

    In the next 6 frames, wheel torque (or torque at the wheel) is calculated for each rpm interval, for each gear.
    The formula is straight forward:
    It takes the engine torque at that rpm, multiplied by the ratio of the specific gear, multiplied by the transfercase ratio, multiplied by the diff ratio. All these figures are from the brochures and graphs.
    This is done for all rpms and all gears, for both engines.

    Then lastly we return to the first sheet named "Comparison":

    Here I list the wheel torque at corresponding rpms for both engines, and each frame covers a gear.
    A theoretical road speed is calculated using the tyre circumference from the link in post #1.
    Using the Engine rpm, divided by the gear ratio, divided by the transfercase ratio, divided by the diff ratio, gives us the rpm of the wheel/drive shaft. This, multiplied by the tyre circumference in millimeters gives us mm/minute. Take that times 60, gives us mm/h. And that divided by 1000000, gives us km/h.

    Notes on the comparison:

    This was a very interesting and very close comparison.
    But, very much the same as the Tritons from the same brand.
    The diesel is about R20 000 more expensive than the petrol, but again, the lack of consumption figures means we cannot calculate how many km that translates to.

    To about 10km/h the petrol accelerates faster than the diesel, due to the higher torque available at the wheels.
    From 10 to about 15km/h, both are damned equal, with the diesel having a slight advantage by the time it reaches 1500rpm.

    Only then does the diesel really get on boost, and the torque at the wheel climbs very rapidly.
    But it only takes the petrol an additional 1500rpm to match and then surpass the diesel in terms of torque at the wheels. At 3500rpm, the petrol has a slight advantage over the diesel.

    From there it's pretty much like the Tritons.
    The diesel has to shift up, while the petrol can remain in it's current gear and have the advantage of the higher gear ratios.

    There is an interesting complication though.
    The steep drop-off in torque that we see in other turbo diesels is even more pronounced on this next generation example. It's so bad in fact, that redline shifting does not produce maximum acceleration.
    Let's take the shift from 2nd to 3rd gear as an example.
    In second gear, at the redline we have 1920Nm available at the wheels.
    Once we shift to 3rd, the torque at the wheels actually goes up to 2194Nm.
    But, if we shift at 4000rpm (2600Nm), we will be in 3rd at 2303Nm (73 km/h), which is more than both instances of the shift at 4500rpm.

    This limits the rev range of the diesel even more.
    The rpm band that'll be used for accelerating to speed, or overtaking is thus only the 3000-4000rpm band. If the engine drops below 3000rpm, better performance can be had, by forcing a down shift. If it revs over 4000rpm, better performance can be had by using the next gear.

    The reader can follow the blue text through the gear shifts. Take care to note that optimal shifts on the diesel might not be at the redline.

    Additional Notes:
    1) Wheel Torque, or Torque at the wheels here is a term I use in a colloquial sense, in that I refer to it almost as the output on a single shaft, while it will be split 50/50 on an open diff. The figure can simply be divided by 2 for a rear wheel drive only, open differential drive train, on tarmac.
    2) I do not have the maximum speed figures available, and could not find them in the brochures, hence the calcs are done to redline in every gear.
    3) I would like to add some more calculations in order to actually calculate a theoretical top speed based on all applicable variables. It would just be nice to see how close it is to actuals.
    4) I would like to add a low-range section, though the overall picture would not change, since the low range ratios are also exactly the same on both models. Just for the sake of being complete.
    5) I would like to obtain fuel consumption figures for both these vehicles in order to calculate how many km are needed to justify the additional cost of the diesel, assuming that the vehicles are under a maintenance plan, which negates any maintenance costs.
    6) Price link: http://www.mitsubishi-motors.co.za/M...t1/default.asp
    7) Tech Spec Brochure link: Thanks AlexF for the Aussie brochure!

    Conclusions:
    1) From the data it can now be seen, that the turbo diesel has an acceleration advantage over the petrol from 13-27km/h. From 0-12km/h the petrol is faster, due to the turbo not spinning fast enough yet to provide sufficient boost. From 27km/h onwards, it's pretty much a one horse race through the remaining gears, because the petrol can remain in the lower gears for longer and thus benefit from the reduction ratio of that gear, while the turbo diesel has to shift, and lose gear ratio advantage.

    2) It should also be noted that the petrol actually makes more torque at the wheels in large parts of it's own rev range, and even in the overlapping rev range.

    3) From the Comparison table, the reader can now also pick any speed to accelerate from, and compare the wheel torque on both vehicles in their suitable gears, and the petrol will again outperform the diesel almost every single time, for given ranges.

    4) What the figures do also show is a very narrow rpm band for the turbo diesel that should be used under acceleration. Only 1000rpm wide from 3000-4000rpm

    5) Maintaining a constant speed in a gear that leaves the engine running between 2000-3000rpm is done with less driver effort in the turbo diesel. Where the turbo diesel might be able to maintain a constant speed up a hill, as the accelerator is slowly depressed all the way to full throttle to maintain constant speed. The petrol could require a downshift if the hill is sufficiently steep to overcome the available torque at the wheels.

    6) At the very low rpm ranges, that's used during obstacle negociation, the petrol and diesel are equally matched, because the turbo diesel is virtually naturally aspirated at those very low rpm ranges (Idle - 1500rpm).

    Summary:
    The Conclusions (listed above) address most of the 8 Introduction and Aim points as listed in post #1.
    Additional data like fuel consumption is required to address, the missed points, and further objectives.

    Edit:
    The latest xls file has been added to include some informative graphs.
    As requested, even performance at reef is compared.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Attached Files Attached Files
    Last edited by RedLineR; 2011/05/02 at 10:53 AM.
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    Reserved - Stall Torque Ratio, Surging
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    Reserved - Torque and Traction
    Last edited by RedLineR; 2011/03/28 at 10:54 PM.
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    Reserved - Extra 2
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    I can't wait for the results

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    Default ULTIMATE Petrol vs Diesel thread - Comparison

    This thread should be moved to the "People with way too much time on their hands" Category.

    I will, however, monitor your study to see that it is scientific & not just petrolesc propaganda...

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    Quote Originally Posted by ThysleRoux View Post
    I can't wait for the results
    WHY??

    We already know the results, they were posted in the first post.

    All we are waiting for is somebody to manipulate some spread sheet figures to correspond.

    Sorry, but if somebody says

    - I am going to do some tests and calculations and see what the outcome is - I would go along with that.

    But when somebody says

    - These are the results, all I have to do now is dream up some tests and calculation to veryify them - Then the system is biased and squewed before it even gets off the ground.

    I have no specific opinion on this issue. I have a Diesel V8 Range Rover and a Petrol V8 Range Rover, and I know and love/hate the characteritics of both. I would hold the same view about any experimentation/tests/calculations. Its a basic principle of research and development.

    Keith
    Last edited by Fluffy; 2011/03/26 at 01:47 PM.
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    Keith,

    You are correct from a pure science point of view. We always say: "don't marry your model". One can suspect that RedLineR is married to his model and has a need to justify the marriage.

    That said:

    I think RedLineR knows his model very well and is tired of people always insisting that turbo diesel low rev torque is the one and only answer to 4x4 driving. I think he is going to a lot of trouble to educate us and to show us the light.

    RedLineR, thanks for the effort and lets get some results to peruse as soon as possible. I have owned both 3.2 DiD and 3.8V6 MIVEC Pajeros and find it almost impossible to chose a winner.

    Roelf

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    Quote Originally Posted by RoelfleRoux View Post

    That said:

    I think RedLineR knows his model very well and is tired of people always insisting that turbo diesel low rev torque is the one and only answer to 4x4 driving. I think he is going to a lot of trouble to educate us and to show us the light.

    RedLineR, thanks for the effort and lets get some results to peruse as soon as possible. I have owned both 3.2 DiD and 3.8V6 MIVEC Pajeros and find it almost impossible to chose a winner.

    Roelf
    Please dont get me wrong, and thanks to RedlineR from me also.

    Having re-read the posts I see now that the purpose of this all is to show just one aspect (apart from the cost of ownership issue) of the Diesel vss Petrol debate, namely the performance at low revs in a 4x4 situation.

    Good luck, the modelling is not going to be trivial. I would go so far as to say that the problem is so complex that it would need the attention of a Masters Thesis to be really conclusive.

    Keith
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    Thanks for encouragement.
    I'm actually quite far with the calcs already, with the Mitsubishis, which were the first complete set.
    But, got a "surprise" visit from family.
    So it's Brandy & Coke time! With the added bonus of time with my old man!
    I'll work some more a bit later, but I promise to have some figures this before the sun rises!

    PS: Ran the arguments past my dad and uncle (both in the mechanical engineering field), and I'm more confident than ever!
    Though it does knaw at the back of my mind, that I might come up short. But that's life. The numbers don't lie.
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    Quote Originally Posted by RedLineR View Post
    ................ The numbers don't lie.
    An auditor taught me that numbers are patient. You can always tweak them to suite your need.
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    Quote Originally Posted by Henris View Post
    An auditor taught me that numbers are patient. You can always tweak them to suite your need.
    True - IF they're your own set of numbers I am sure RedL is going out of his way to ensure that the "numbers" are checkable and not his own.

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    Ya no, it's great that people are critical before anything is published...
    I don't suppose I can use the same argument and point out that you can't critisize something Before it's published?
    Or will I be pushing the limits of logic here?

    People are heading to bed here, so I'm back to crunching some numbers, and maybe I'm bending some slide rules! Who knows?!
    Last edited by RedLineR; 2011/03/26 at 09:50 PM.
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    waiting patiently
    -

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