As I came to halt at some stationary traffic, I pulled up beside two girls in a Swift Vdi. The traffic started moving and slowing down again and again. As the one driving the car stepped on the accelerator the car would move forward lazily when all of a sudden the turbo charger would kick in and throw the girls firmly into their seats. It was hilarious as the trend in traffic continued for a while and every single time their car slowed down and accelerated they would be thrown backwards into their seat.
They must have been thinking there was something wrong with the car. But, actually there wasn’t. You see the Swift diesel is equipped with a turbo charger. Let me explain what was going on and how the turbo charger was causing it.
A turbo charger is a forced induction system that can be incorporated in a naturally aspirated engine. A turbo charger works on the principle of kinetic energy. A common shaft connects a turbine and a compressor. The turbine is placed in the exhaust manifold and the compressor is mounted on the engine behind the front grill or an air scoop under the bonnet where there is adequate airflow when the vehicle is moving.
Acceleration causes increase in flow of exhaust gases which spins the turbine in the exhaust manifold which via the connecting shaft spins another turbine in the compressor resulting in air being sucked into the compressor. The compressed air which is dense is fed to the cylinders thereby increasing the fuel/air mixture which results in increased power output.
However, there is a downside to turbo charging an engine. At low speeds there are not enough exhaust gases in the exhaust manifold to provide adequate pressure to spin the turbine of the turbo charger. As a result, when acceleration is increased suddenly there aren’t enough exhaust gases to spin the turbine and increase airflow to the engine to significantly increase acceleration of the vehicle. This delay in increasing acceleration of the vehicle is called turbo lag.
It is only after a while that the increased throttle input burns more fuel to create enough exhaust gases to spin the turbine of the turbo charger thereby creating suction in the compressor and increase airflow into the cylinders which increases acceleration.
The sudden boost of air by the turbo charger into the cylinders results in a sudden surge in acceleration which throws the driver and passengers into their seats as the car shoots forward all of a sudden. This is the reason why you may feel that your vehicle does not accelerate well in a particular gear at a particular speed and jumps forward all of a sudden under acceleration. It’s not witchcraft or a malfunctioning engine, its turbo lag.
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