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Originally Posted by smartcat Let's take a look at the curious case of 2.0 TDI engine which is shared between Volkswagen, Skoda and Audi. This engine is available in four states of tune - from 110 BHP/250 Nm to 190 BHP/400 Nm. The advantages of having a single engine with different power/torque outputs are obvious - you don't need to have 3 separate engines for 5 or 6 models. |
Here's a few things I know that may help explain this. If one assumes that there is a specific engine and block design, as your example shows, then the differentiation in power is for the following reasons, in no particular order:
1) ECU Tuning
2) Turbo size, pressure setting and also FGT vs VGT
3) Valves & such that allow air and fuel in to the engine.
4) Not related to power, but for reliability, some manufacturers may put stronger connecting rods, and other mechanical bits into their higher powered units compared to lower powered units.
Now the official ARAI figures for these engines is actually misleading. Typically speaking, the 110 hp engine will pump less fuel into itself during acceleration from, let's say a traffic signal, than the 190 hp, under the same amount of accelerator input from the driver. Once cruising, say 50 km/h in city driving, both engines would use a similar amount of fuel to maintain a similar speed (of course assuming the same identical car). This is because you need a certain amount of power and torque at the wheels to move a particular mass at a particular speed.
The real differences in real world driving are because the 110 hp can run more lean than the 190 hp as they are being asked for different outputs. In real-world conditions, an Octavia 110 2.0 would be more efficient than an Octavia 190 hp 2.0, by a fair amount of kmpl I might add. This is because lean, mechanically efficient engines use lower fuel than rich, mechanically efficient engines.
The second part of this argument is
reliability and longevity. In general, an engine tuned down and running efficiently will last longer than the same engine tuned up. This is the reason why cars have bigger engines. Example: VW's own 1.6 TDI makes the same power/torque figures as the 2.0 110 hp model, so why not put the 1.6 in - it's for reliability and longevity. VW's 110 version of their 2.0 liter is popular with their commercial van customers in EU and with taxi drivers all over Europe who drive Octavias. A similar example is the old Innova had a 2.4 diesel tuned conservatively to 101 hp/200 Nm, but the damn thing never broke! Even the new 2.4 is conservative by EU manufacturer standards at 143 hp/343 Nm, similar to VW 2.0 figures and much less than BMW/Mercedes new engines of smaller sizes. Again efficiency and reliability are key. Another factor in the reliability argument is that a tuned-down bigger engine tends not to struggle at low RPM, compared to a high-tuned smaller engine in the same car - hence the "driveable" nature of the old Innova even though it was underpowered. This is part of the
no replacement for displacement argument. A similar example - Toyota Etios with just 68 hp from 1.5 liters. However, you will easily find a 5,00,000 km Etios taxi in the near future, once its old enough, with a smiling owner.
In an ideal scenario - I'd have a car with different maps that affect fuel flow as well as turbo boost, so I can drive a 110 hp in traffic, cruise in a 140 hp on the expressway and attack a ghat at 190 hp. Of course this may not be achieved in non-fantasy-real-world.
The relative difference in price of different engine options in the VW range, on the same car, depends on:
1) Components used within the engine - which is hardly different to be honest
2) Other things on the car, such as a 5 speed lower torque gearbox, Fixed rear suspension instead of multi-link, smaller brakes or drums at the rear instead of discs and many features such as different in-car entertainment, different interior trim, etc etc.
Hope this helps!