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I'm considering to have my car engine chip tuned. I'd like to increase the fuel efficiency of the engine. Increasing the power of the engine would be only a secondary advantage of doing so. Most of the chip tuning companies in my country offer tuning for max power or for max fuel economy.

My question is this: is there anything like economy car engine chip tuning that really works? How much improvement can I expect or what are your real-life results (if any)?

I know there are other ways of increasing fuel economy (mileage), but this is an important one. There is a general consensus that bigger and especially diesel (turbo) engines are better to tune. My car is a 2007 VW Golf 1.9 TDI, but I wouldn't limit answers by that.

  • Do you have any other constraints? Usually, engines are tuned to produce a good balance between fuel economy and power, for the customers the car company hopes to attract. However, there also will be considerations given to laws that regulate the vehicle's emissions. If you are willing to break those laws, or live somewhere that doesn't have such laws, maybe fuel economy and power are your only two variables. But, normally, you need to obey emissions controls, and with very few exceptions, I'd say that's a good idea for people interested in sustainability. – Nate Oct 1 '13 at 9:06
  • Also, you probably know this already, but for your specific engine, I would also ask around at the TDIClub forums. Not everyone there cares about sustainability, but there's enough TDI owners who do care about fuel economy, for one reason or another, that you might find some good experience. – Nate Oct 1 '13 at 9:08
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    @Nate: The default car production balance is not bad, but it's a general default for this car/make. By tuning this (one) engine you can improve the performance and economy. Yes, my idea is to keep the existing emission limits (I have the emission check every other year) and I even expect to lower the emissions. Nice link too. – Peter Ivan Oct 1 '13 at 22:47
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Yes, many tuning stations offer a range of options.

The most popular is to offer power upgrades, usually at the expense of fuel economy, for example improving fuel/air/compression balance at low speeds for high acceleration, or altering tuning at high revs to increase top speed.

One of the tuning techniques to improve fuel consumption is to alter your car's mapping to give a much flatter torque curve, this allows a driver to control the fuel usage, and manage predictable gear shifts earlier than they otherwise would (short-shifting)

In reality, though, you can get the same (or better) gains from just changing your driving style. Coasting, short-shifting, avoiding braking where possible, limiting your top speed, over pressuring your tyres etc.

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There are different types of chips, some increase the pressure in the fuel rail to gain power, this are not looked on favorably by vehicle manufactures as they are increasing pressures beyond factory specifications. Alternate chips optimize the air to fuel ratios and other settings using the vehicle original ecu. These chips will not void your new car warranty as they are using the safe guards on the original computer. Any gain in power can be used to you advantage, if you drive economically, the vehicle will use less fuel for the same speed prior to adding the chip, on the other hand, you now have more power, so you can also use more fuel if you don't drive efficiently.

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I would say that the OEM engine tune is sufficiently developed to be as lean as possible relative to the fuel octane.

And so improve fuel economy by increasing the tire pressure. Also, shorter sidewall tires are possible. For instance a 205/50-15 tire and a 205/45-16 tire have about the same diameter and width but the 205/45-16 tire has a shorter sidewall.

If a manual transmission, then improve fuel economy by not lugging the engine and by not highly revving the engine. Shift the transmission to be in the correct gear at the correct time. Otherwise get an automatic transmission.

Now a front air-dam will improve fuel economy but a front air-dam can have a larger effect on reducing aerodynamic lift at the front than at the rear and therefor there is a risk of a high-speed aerodynamic oversteer. So current technology more often uses a front splitter and then smoothing panels on the underside of the car.

A rear lip spoiler will improve fuel economy but only have a small effect on aerodynamic lift at the rear.

Strangely enough a stiffer suspension will improve fuel economy because a stiffer suspension produces faster weight transfer and faster weight transfer results in less tire drift in ordinary driving. (Tire drift is what a tire does when it is not sliding. The sport of drifting is really the sport of power-sliding.)

There's no easy answer in exhaust systems. Current cars mostly need a tune just to use a low-restriction cat-back exhaust. For instance, popping sounds from the cat-back are due to un-burned fuel in the exhaust system. At least the electronic tuner then has something to tune-for.

Easy choices, but expensive choices, of vehicle weight reduction are available in AGM batteries, with premium racing style wheels, and in stainless-steel exhaust systems. The AGM battery can simply be smaller than the OEM gel battery.

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It is very unlikely that a chip tuning, almost every time developed by small companies, can surpass the factory tuning, considering that:

  • tuning requires controlling at least 10 parameters (in the last 10-15 years, more nowadays) in a range of rpm which should be split in several points, let's say 5-10 from minimum to max rpm. If you do the math, we are talking about 5 to the 10th power. Even assuming optimisations here and there, it's several thousands of combinations which need to be taken into account. NO small company can do that.

  • tuning for emissions is difficult to reach even for big companies because it affects other more interesting parameters such as power and fuel efficiency. It's extremely unlikely that a small company can improve fuel efficiency 1) significantly at all, and 2) not significantly but without hugely affecting emissions. If it were possible, the car companies would have done it already.

So no, tuning usually gives you more power, but even if in theory it could give you a fuel efficiency gain, in fact it will increase emissions a lot more to get that. Example: the FIRE engine from FIAT was developed to run lean and efficient, but it produced NOx. When the NOx emissions started to be regulated, the fuel efficiency worsened for few years. In any case, the worsening was minor, so even with the increased emissions you would get only small improvements.

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