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Concepts
Petrol vs. Diesel
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Much off-roading is done at low speeds (
as
slow as possible, as fast as neccessary
), using
a lot of power. This requires an engine that produces high amounts of
torque at low revs (aka grunt). Diesel engines, by their very nature,
are low-revving, high-torque engines, although modern, purpose-built
petrol engines have similar characteristics. Entire rain forests have
been destroyed documenting the virtues of one or the other, and I
present some arguments in favour of each.
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Diesel Engines |
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As mentioned above, diesel engines are well-suited to off-roading
because of their low-revving, high-torque nature. However, diesel
engines are much less responsive than petrol engines. Other
considerations include availability of diesel, and their suitability
for wading.
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Availability of fuel in your country must be the first consideration.
Diesel is available almost everywhere, although, because of its high
sulfur content in widespread areas (such as Africa) require a very high
degree of maintenance and therefore cost. Diesel injection systems are
complex and therefore difficult to understand, and expensive to fix or
replace, especially in remote areas.
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Lastly, because diesel engines induce combustion through compression,
they are well-suited for wading through water.
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Petrol Engines |
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Petrol engines, on the other hand, produce similar torque, but at much
higher revs. This becomes especially aparent when descending steep slopes,
as it will be seen that diesel-powered vehicles descend much slower than
their petrol counterparts. Bear in mind, however, that a large engine in
a small car (such as the 4.0l straight six found in the Jeep Wrangler)
provides an excellent power-to-weight ratio. Even though maximum torque
is produced at higher revs, it will still descend a slope slower than a
Defender TDi or Pajero 2800 Turbodiesel. Petrol engines are also much
more responsive than diesel engines. "Feathering" the throttle in a petrol
engine, coupled with effective clutch control, allows for greater driving
control and better driving flexibility than diesel-engined vehicles.
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Of course, most mechanics world-wide understand petrol engines, and
frequency as well as cost of maintenance and repairs are substantially
lower than on diesel engines. On the down-side, however, many modern
petrol engines use electronic injection systems which can be as complex
as diesel counterparts. Further, most modern petrol-powered four wheel
drives run on unleaded fuel, which is not always readily available in
remote countries such as Morocco, Mozambique and Zambia.
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The last point worth mentioning is that while practically feasable and
still cost-effective, it is much more difficult and expensive to
water-proof a petrol engine for wading than it is a diesel engine.
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© 1998-2013 Martin Wittenburg and Michael Wittenburg. All rights reserved.
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