Which size van engine should I choose?
Looking at vans can often seem confusing, you have chosen the van that suits your needs it’s comfortable to drive and at the price that suits your budget but it’s available in 2 engine sizes with different PS values. When you look through each model’s specifications it will list features such as Maximum Power 100ps @ 3500 rpm, and Maximum Torque 276 lb/ft @ 2000 rpm so what do these terms mean?
Where does the term horse power come from?
In the 18th Century James Watts a Scottish Inventor and Engineer radically changed the efficiency of steam engines and tried to commercialise his invention. At the time work horses were seen as the cheapest form of power especially for the mining industry. They were used for powering mechanical winches where the horse would walk round and round turning a big wheel all day that would lift buckets of water or coal from underground. Watts needed to prove to the mine owners that steam power was cheaper and more efficient than the use of horses. To sell his invention he looked towards mathematics and the relationship between a horses power, how much work was being done and how much time it took to do this work. In 1782 Watt formed his mathematical formula for calculating power a term which today we still refer to as horse power. It worked on the principle that a horse would continually turn a work wheel of a certain radius x number of times in 60 seconds. To achieve this, the horse needed to constantly exert x amount of force to raise the heavy bucket from the mines below.
Through a series of calculations Watt was able to work out that a horse was capable of producing power in the ration of 33,000 ft-lbf/min. This is the equivalent capability of being able to lift a 75kg weight a distance of 1metre in one second or the energy it takes to move a 149kg object 100ft in one minute. With the help of this formula Watts was able to prove to the mining companies that his new improved steam powered engines were more cost effective and efficient than the use of horses.
What is Horsepower?
Horsepower (HP) is basically a measurement of power and the rate at which an engine can do work, so what does this mean to the average van owner? Well in simple terms horsepower refers to the maximum rate of acceleration and the top speed of your van which can be expressed as the following calculation.
Horsepower(PS) = Torque(Kg) x RPM(Engine Speed) / 5252
Why is Horsepower important?
When you are driving on the motorway and want to overtake another vehicle the more horsepower you have the more responsive your van will be when you put your foot down.
Horsepower has a direct relationship to an engines RPM which is why you may find that when you are travelling fast and drop a gear, the acceleration of the van is more responsive than at a higher gear. This is because each engine will have a maximum horsepower point which is what the technical term Maximum Power 100ps @ 3500 rpm which means, that at 3500 rpm the van will reach its maximum power, which will give the most response when you put your foot on the accelerator. After 3500 RPM the power will start to drop off meaning the vans acceleration won’t be as quick.
Why are vans engines marketed with different units of power?
The Automotive industry widely uses the term horsepower to list the maximum power of their engines as a selling point. This can sometimes become confusing as there is more than one unit of measurement for an engines power. Where as one manufacturer may list the engines power output as KW another may use bhp and a third manufacturer may use PS. The three main measurements used bhp, KW and PS are all use in the auto industry to market an engines power but each measurement gives a slightly different result.
What is bhp?
Break Horse Power or bhp as it is referred to is the most commonly used measurement for marketing an engines hp. HP refers to the engines total output of power, bhp on the other hand takes into consideration that the engine has to power parts of the van like the alternator, water pump, gearbox etc each part draws a certain amount of power and what’s left if the bhp.
What is PS?
PS is a German unit of measurement which stands for Pferdestärke (translation means “horse strength”) it is widely used thought Europe and when compared to bhp is slightly higher.
What are KW?
Kilowatts (KW) is the least used of the 3 units of measurement for expressing a van engines power, where 1 KW is approximately 1.34 bhp.
Converting units of power
100bhp = 101.4PS or 74.6KW
Use one of the following formulas for converting between units of power.
BHP = PS x 0.9864
BHP = KW x 1.341
PS = BHP x 1.0139
PS = KW x 1.3596
KW = BHP x 0.7457
KW = PS x 0.7355
So what is Torque?
Torque is the twisting power or rotational force that turns an object and can be thought of as the pulling power of the engine at low revs. The simplest way of explain torque would be to look at the act of tightening a van wheels lug nut. By using a wrench we apply force by either pulling or pushing on the handle which creates a torque on the lug nut, which turns the nut if enough force is applied. Torque is expressed as weight/distance (lb/ft) to calculate torque you multiply the force being applied by the distance from the centre (which is why having a long wrench makes tightening a wheel lug much simpler).
Why is torque important?
When you start the engine its torque that gets the van moving from its stationery position it’s also torque that powers a van up a steep incline. Starting and stopping an empty van wont display any noticeable drop in an engines performance, but as the vans load increases the added weight being carried puts an increased demand on the engine which is where talk becomes important. The higher the torque the less effect loading the van will have on its performance. Where as a van with a low torque will start to have a considerable performance drop once the van is loaded with a heavy load. A van with a high torques will have a more consistent performance whether the van is carrying a heavy loaded or not.
The higher the torque the more powerful the pulling power of the engine.
Any van that is going to be used for towing additional equipment required a lot of torque. Each van will have a maximum towing weight specified in the vans spec.
It’s torque that lets you do the hard work but horsepower that lets you do the work quickly once the van is moving.
Vans tend to have a choice of one or two engine sizes but different PS/torque values; if the van will constantly be used for carrying heavier loads consider the larger engine with the higher PS value. It will have more horse power and torque and hence perform more consistently under heavy loads especially on hills and stop/starts.
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