Article reproduced by kind permission of Mike Fishwick

Many people ask if it worth having their engine management system remapped, the answer being that it works well, with no snags other than the cost – unless you plan to keep the car for a long time, or it has an annoying flat spot, then perhaps it is not worth paying for – that depends on the owner’s priorities.

The theory is that the manufacturer finds the optimum setings in terms of power, torque, and economy, but then has to adjust them to meet criteria such as exhaust emissions, and in particular those involving oxides of nitrogen (NOx) which are formed during the peak temperature of the combustion process.

This means that the easiest way to meet the emission regs is to reduce the combustion temperature by richening the mixture, and retarding the ignition timing, neither of which do anything for maintaining peak efficiency.

Once the engine is in production, the regular tests in European countries, such as the MoT, TuV, and Controle Technique etc, only check on emissions of carbon monoxide (CO) and – in the UK – unburnt hydrocarbons, but NOT NOx.

In some cases the power output may also have been reduced to satisfy power limitations imposed my insurance categories and other legislation.

This means that a remap can re-set the engine efficiency to its original level and NOx levels, so bringing improvements in power, torque, and fuel economy.

The best remap is one which after downloading the new program to the car’s management system is subsequently adjusted on a rolling road – known as a Live Remap – which will usually gain a little over a basic (generic) remap.

However, a company which has plenty of experience of your particular engine will have optimised their program on a rolling road anyway. As engines of the same type are usually within a few horsepower of each other, the benefit of a live remap will be limited, unless you have modified the engine with different manifolds (inlet or exhaust) a larger throttle body, or different camshafts etc.

The current market leader seems to be Chipped UK, but my 2.8 Z3 was given a live remap by our local Superchips dealer about ten years ago, and it gained about 7 bhp, 10 lb-ft, and about a 10% improvement in fuel economy.

Although the peak power and torque gains for a normally-aspirated petrol engine are seldom more than 10%, they may be less if the original mapping was as close to the optimum as possible. The gains in the mid range are, however, proportionately higher, making the car more drivable and a lot more economic.

Do not, however, expect miracles, such as are possible on a good turbocharged diesel! Our 1.9 litre Golf TDI was remapped by AMD of Bicester, and went from 115 bhp / 210 lb-ft to 165bhp / 275 lb-ft. The torque curve is now flat from 2000 rpm to 4000 rom, so it it pulls sixth gear (35 mph/1000 rpm) happily from 40 mph, and is still doing so at 125 mph+, effortlessly out-accellerating just about anything it meets. It is even more economic, with up to 60 mpg on a fairly quick run – the future is here – and it’s diesel powered!

As with the standard BMW petrol engine map, the modified ones are optimised for 98 octane, so before it is done, run the tank down and fill up with 97/98 octane fuel, after finding the best available locally in terms of fuel consumption at a steady speed on a flat road, such as on a motorway.

My 2.8 litre Z3 usually returns 37 mpg at 70 mph on UK motorways using Esso 97 octane fuel, and 34 mpg at 80 mph in France, using supermarket 98 octane – in France this is just as good as ‘real’ petrol. At lower speeds it is outstandingly good – on a 220 mile run from Gap, in the French Alps, to a point south of Clermont-Ferrand, all on country roads at about 60 mph, with a little overtaking, it managed 42 mpg!