The most evident benefit of tuning your petrol or diesel engine is the increase in performance. Both power and torque are substantially increased, often by as much as 20-30% or more. This increase in performance from the tuning of your engine, often makes the car feel as though it's lighter, as well as giving much more progressive and linear acceleration, making for easier and safer overtaking..
Most notably the common turbo lag and hesitation in most cases is reduced or eliminated. No more waiting for the turbo to spool at 1750rpm, increased torque is now available from as low as 1200rpm and in a much more linear release, instead of the usual lag then push. The engine revs much more freely, is more reponsive to throttle position and makes driving much more fun and enjoyable. It is sometimes normal that the maximum speed of the car is also increased.
As well as improving overall performance, the system also allows your engine to run more smoothly and efficiently. Due to this, the fuel consumption is also improved due to the fact that the engine is having to work less to gain similar results in terms of speed. It is often found that you need a softer touch on the throttle compared to the standard tuning when staying at a certain speed, 30mph for example. This means the engine is producing more power, with less throttle, improving the efficiency of the vehicle.