As you can see from these pages, I am very sceptical about bolt-on fuel "saving" gadgets. My general advice to anyone who thinks they have invented a miraculous fuel "saving" device is: forget it. The chances that your device really works are very slim, and you are almost certainly wasting your time and money.

Sadly, many clever and inventive people have wasted a lot of time and money on this quest. Over and over again people "invent" ideas that have already been thought of, extensively researched and then rejected by industry, because either (a) the benefits are much less than expected, or (b) some critical problem (eg NOx emissions) means the idea cannot be used in practice.

However, the rewards for someone who invents a device that really does work are extremely high, and in addition the benefits to the planet and the car industry of such an invention would be great. So I don't want to discourage people too much, and so here are some guidelines for inventors.

Firstly, do your research. For starters, look at every page on this site and make sure you understand the technical arguments against the fuel "saving" devices currently on the market. Also read plenty of books and Internet articles on the subject.

Next, make sure you work on a new-ish vehicle. Many inventors try their ideas out on old cars with carburettors and contact-breaker ignition systems. Such systems have already been superceeded and a device that only improves old cars has a very limited market. Even traditionally less advanced countries are now introducing electronic engine management, catalysts and lambda sensors - this should be your minimum standard of test vehicle. Ideally you want something with on-board diagnostic capability, for example a European car from 2000 or later.

Thirdly, you need good test equipment. To check the effect of your device on emissions you must measure CO, HC and NOx as a minimum. NOx emissions analysers are not easy to find but it is absolutely essential since a reduction in HC and CO at the expense of increased NOx is trivially easy to obtain.

To see the effect of your device on the engine, use a car with On-Board Diagnostic capability (as described above) and get hold of a Scan-Tool. With this you can read all kinds of useful parameters such as fuel flow, lambda, ignition timing, etc.

Finally, the only way to actually prove your device out is with rolling-road tests as described here. This will cost several thousand pounds to do properly but there is simply no alternative, as any on-road measurement is subject to external factors such as traffic and weather that make the result meaningless.

Most people who have (allegedly) invented a fuel "saving" product sell it on the aftermarket, ie sell it to drivers so they can "upgrade" their cars. But the real money is to be made in selling directly to car makers for fitment as standard equipment. If you invent a fuel saving device that really works, and you can prove it to industry, then you could sell perhaps ten million units a year. Aftermarket sales will always be very small in comparison.

One last word: don't send details of your invention to me unless you have adequately protected yourself, for example by means of a patent!