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.

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