Most tuning work takes less than an hour to complete. In general, diesel engines offer better results than petrol ones for tuning specialists and yield the best power increases. That is because petrol engines are usually highly tuned already and would require costly changes to a number of components to make the increase in bhp worthwhile.
Consequently, chipping a petrol engine costs around £270 and often boosts performance by a lowly 12bhp. A diesel can be reworked for £500 and provide an increase of up to 60bhp (depending on the size of the engine).
Chipping doesn’t normally affect the top speed of a car but it will increase the torque and acceleration. Tuning firms claim that in many cases the work will also boost fuel economy by cutting down on gearchanges.
Drivers should approach such work with caution. Car makers warn that meddling with the engine can invalidate a warranty. However, this is a grey area and chipping companies claim the adjustments are often undetectable to a mechanic carrying out warranty work.
Insurers are sometimes reluctant to cover a car that has been tuned and policyholders are required to inform them of any modifications to a vehicle. Owners who do not tell their insurers run the risk that their vehicle will not be covered in the event of an accident.