Fuel Savings vs Time Savings
The difference between civil and country
roads could be affected as you say by the fuel flow rates... but I think it is more connected with driving at a constant
In civil town driving you are constantly changing speed with the traffic flow and stop / starting at junctions
etc. When you pull away, you usually have your foot to the floor to accelerate away and when the throttle is to the floor the
same amount of fuel is going into the engine regardless of whether you have a magnetic unit fitted or not... with the
magnetic unit fitted and your foot to the floor you will accelerate away faster as you use up the extra power produced by the
To see savings you need to be travelling at a constant speed as with country driving which is why you see better
savings on long constant speed journeys. As you know, the Max units give more power output from the same given volume of
fuel. The vehicle's throttle pedal controls the amount of fuel entering the engine.
For example, say the throttle is
at an angle of 45 degrees to maintain a constant speed of 70mph without a unit fitted. You then fit a unit and continue to
drive with the throttle pedal at an angle of 45 degrees, exactly the same amount of fuel is being fed to the engine and the
consumption will be exactly the same regardless of whether there is a magnetic unit fitted or not. But because the unit is
fitted there will be more power output for that same given volume of fuel and so the vehicle's speed will increase to say
73mph for that same given volume of fuel. Now if you lift your foot off the throttle pedal to say 42 degrees to reduce the
fuel flow going into the engine and drop the speed back to the original 70mph again there is now less fuel flowing into the
engine to maintain the same constant speed and you will see the savings.
As mentioned above, during civil driving, the
throttle pedal is often flat to the floor which will use the same amount of fuel regardless of whether a unit is fitted or
not. During country driving at a constant speed the throttle will be higher up, thus feeding less fuel to the engine to
maintain the same previous constant speed. If the throttle is maintained at the same point as it was before then the vehicle
will travel faster and the savings will be in the time taken to get from A to B as opposed to fuel savings.
why it is so difficult to test the units as it is so easy to use up the extra power by travelling faster. Ideally, as
mentioned before, constant speed driving on a track circuit in constant conditions would be the ideal scenario.
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