Devices of this type include Z-Stab / EZ-Stab, Pivot Raizin

As well as the air and fuel related devices decribed elsewhere on this site, there are also many products that claim to improve economy and/or power via changes to the vehicle electrical system. Chiefly these are grounding wires (to fit between the engine block and the vehicle body) and various voltage stabilisers.

Certainly poor electrical systems can cause significant problems. Most obviously, a poor earth link between the engine and body makes starting very difficult, since there is a large voltage drop when the starter current (100 - 200A) passes through the high resistance. What is far less clear is that a vehicle whose electrical system is in pretty much "factory" condition could benefit from adding an additional grounding strap.

Another class of device is the add-on voltage stabiliser. Now, there is no doubt that vehicle electrical systems are inherently "noisy" (due to ignition, alternator, etc), and it is not hard for me to see how an add-on device could smooth this out. The electrical details of these devices are of course kept secret by the makers but some educated guesswork is relatively straightforward! Assuming that these devices do reduce noise in the electrical system, it would not be unreasonable to expect benefits such as:

• Better sound from the in-car entertainment system
• Smoother idle, especially when switching electrical devices on/off
• Steadier light from headlamps; increased bulb life
• Possibly sharper throttle response, especially from low engine revs and with a nearly-flat battery
• Possibly better starting with a nearly-flat battery

Where I am less convinced is when the claims are extended to significantly improved fuel economy or torque / power. Modern vehicle wiring and ECUs are already designed to operate in a harsh electrical environment. They cope with conditions from maybe 8V starting with a nearly-flat battery to 16V on a boost charge, and with electrical interference from mobile telephones etc, without failure. The ECU runs internally at 5V or even less and is heavily stabilised to ensure the processor runs fault-free at all times. Many modern ECUs repeatedly self-check and would shut down the engine entirely if any kind of fault condition occurred. Overall, it is hard to envisage how a more stable electrical supply could significantly improve engine economy, emissions or performance on a vehicle in good condition.

The suggestion made by some sellers of such products, that the alternator on "unmodified" vehicles is always pushing 1 - 2 kW into the battery (and hence "robbing" the engine of this power) also does not fit my experiences. Once the battery is fully charged, the alternator automatically reduces its output (otherwise the continual flow of energy into the battery would cause it to boil and ultimately be destroyed), and the mechanical loading on the engine then drops to a relatively low level - though undoubtedly there is still some power loss.

Equally, extremely precise control of the engine is essential to meet today's strict emissions standards. If electrical problems really did lead to significant errors in fuel delivery or ignition timing on cars in good working order, it seems highly unlikely that such cars could pass emissions tests.

It is also worth noting that engines are generally developed on test beds using highly stabilised power supplies (not using the vehicle alternator), but the test results and ECU settings carry over quite accurately to in-vehicle use - ie there is no obvious worsening in performance with the "less stable" supply.

Improvements of one or two percent may be justified, and again to be fair to the makers of such devices, they do not generally claim implausibly large power or economy gains. Unfortunately benefits as small as this are difficult to precisely quantify without a large number of rolling-road dyno power or economy tests, due to the natural variation inherent in such testing. As with all such devices, while there are many satisfied customers, you can also find people who have tried them and found no obvious benefit.

When it comes to performance benefits, my view is that even quite effective products usually do not justify their purchase on a straight "power increase versus money spent" equation. I would tend to put voltage stabilisers in the same catagory - but as with all performance enhancers, some people are willing to spend a lot of money on not very much horsepower gain for understandable reasons of "making their car special", "liking the different sound", "because it looks cool", etc, and if you want to buy one for those reasons, that's fair enough.

Please also read the general comments on fuel "saving" devices, if you have not done so already.

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