Fuel saving crap

With gas being so expensive now, people are looking for that magic fix that costs $10 and gives them a 500% increase in gas mileage.  As usual, there’s no such thing.  Popular Mechanics tested a number of gadgets and all of them turned out to be snake oil.  Most had no discernable effect on power or efficiency.  A few actually decreased efficiency.  One started an engine fire.

A lot of the comments posted to the article state that these devices did work, despite PM’s experiments showing that they didn’t.  Some state that the magnets were the wrong type or not installed “in phase” and such.  However, the fact that gasoline is not magnetic seems to be a much stronger indicator of how much these magnets can actually help.

It’s very possible that some people did experience mileage improvements after installing the devices.  However, in some cases, people actually stated that they altered their driving patterns or did other work to the car as well (sometimes suggested in the gadgets’ instructions).  A test with two variables can’t prove that variable A is what actually caused the results, especially when variable B is known to produce similar results on its own.  For example, the Fuel Saver 7000′s instructions state that a bad oxygen sensor won’t return accurate readings and therefore you won’t see as much improvement from the FS7K.  What they neglect to mention is that a bad O2 will also result in bad readings and lower mileage even without the FS7K.  Installing the FS7K and a new O2 might give you better gas mileage, but you might have gained just as much from installing the O2 without the FS7K.

Here’s a comment that I posted to the article regarding the FS7K (not yet published).

Looking at the Fuel Saver 7000 “how it works” page (http://www.fuelconcepts.com/how.htm) and the installation instructions (http://www.fuelconcepts.com/install.pdf), there is very little to indicate that it will have much effect on power or efficiency.  You splice a line into your fuel source (either at the schrader valve on the fuel rail or elsewhere in the fuel line) and splice the main unit into your PCV-intake hose.  You calibrate it to a certain number of drips/min depending on your engine size.  The fuel drips down into the main unit and “secondary vaporization chamber”.  The drops of gas (purple dots) and the “light emissions” (blue dots) from the PCV valve “are vaporized through a 3-Stage ‘cold vaporizing vacuum system’” (blue swirly).  This appears to be nothing more than the regular intake manifold vacuum sucking them in (red dots).

Essentially, you’re sucking gas in from an alternate source, which is supposed to be vaporized more fully than the gas from the injectors.  The computer lowers the amount of gas sent in via the injectors to compensate for the gas from the Fuel Saver 7000.  Overall, you’re still burning the same amount of gas, but a portion of it is coming in via the Fuel Saver and is supposed to burn better.

However, there are downsides to this setup.  The Fuel Saver’s “oxygen intake” appears to be just a hole in the canister.  If so, your engine is now sucking in a (tiny) amount of unfiltered air, which could allow foreign materials in (but would most likely be ok).  Because the Fuel Saver is spliced into the PCV line and has its own oxygen intake, there is less vacuum on the PCV valve itself, which means you’re reducing the ability of the PCV system (http://en.wikipedia.org/wiki/PCV_valve), which could possibly lead to engine wear or damage.  They mention tapping a new port in the manifold if you don’t have a PCV line available, and I think it would probably be better to route the Fuel Saver into its own intake manifold port to avoid interference with the PCV system, but that adds a lot of complexity since most engines aren’t going to have extra vacuum ports available.

The whole idea of adding vaporized fuel to a random port on the intake manifold may or may not work well also.  Most modern cars have direct port fuel injection, and the manifold is engineered for flowing only air.  For example, it took a lot of different design attempts to make the upper intake in my GMC Syclone work well with an EGR port.  Introducing things other than plain air into a manifold designed for air simply may or may not work well, depending on the exact design of the manifold.  If the hose carrying the fuel vapor from the Fuel Saver exits in a certain way, the vaporized fuel could condense and simply drip down the intake, which is much worse than the vaporization that the regular injector would provide.

The schrader valve on the fuel rail is designed for temporary fuel pressure testing and such.  Certain fuel rails are known to crack with the added weight of a fuel pressure gauge or other device attached long term.  Another case where it would probably be ok, but it’s safer to permanently attach this to a regular fuel line than to use the port on the fuel rail.

Now on to the actual math behind this.  The L36 3.8L V6 in the Pontiac Firebird uses 22lb/hr injectors.  Figuring that gas weighs 6 pounds per gallon and there are 6 injectors, the injectors can put out a total of 132lb/hr or 22 gallons per hour.  I don’t know the average duty cycle in a real 3.8L car, but let’s assume that they don’t like to go over 80% to avoid stress on the circuitry, and we’ll take half of that – 40%.  Obviously, the amount of fuel going through the injectors will vary, but we’ll just use this as a mid-point guesstimate.  40% of 22 gallons is 8.8 gallons, which is 1126.4 ounces per hour.  That equals 18.773 ounces per minute of gas through the injectors.  The Fuel Saver instructions say that a 3.8L should use 38-42 drips per minute.  A quick test with water from the kitchen faucet showed 40 drops to be about 12cc.  One ounce is 29.57cc.  We’ll figure in some error and just say that the Fuel Saver should be set to half an ounce for the 3.8L.  With a normal flow rate of 18.773oz/min through the injectors, using the Fuel Saver you’re sending 2.66% of your fuel through it rather than the injectors.  At higher RPMs, there will be a lower percentage going through the Fuel Saver (more through the injectors but the same amount through the Fuel Saver), and a higher percentage at lower RPMs (less through the injectors but the same amount through the Fuel Saver).

While the idea of using a device that vaporizes the fuel more thoroughly should increase the combustion efficiency, I don’t think this device can absolutely guarantee that it will even help at all on every single car.  A lot of engineering goes into designing intakes, and a particular intake may or may not work well with this setup.  Also, interfering with the existing PCV system could possibly affect performance or even cause damage over a prolonged period.  This is only theory, and not actual product testing, but I doubt that sending <3% of your fuel through this device can give you a 50% improvement in gas mileage.

There is a line in the patent that states “An advantage of the present invention is that the delivery of a fuel rich air mixture into the PCV system is shown in improve the rate of fuel consumption in the engine.”  However, a quick Google search didn’t turn up anything related to that idea, other than the patent itself.  The device seems to be based on the fact that shooting a rich mixture into the PCV port will improve fuel consumption (lower it?), but there doesn’t seem to be a lot of support for this “fact” that I can find.

Feel free to let me know of any errors you see.  I tried to be as accurate as possible without having 100% exact numbers.  I’m not doing any self-promotion here, and I’d love to see something like this work, but the numbers just don’t seem to support it.

Hopefully that lets you see that there are a whole lot of variables involved with these things.  Depending on a specific car’s design, one of these gadgets might help or it might drastically hurt.  At the very best, it’s a crap shoot whether or not one of these devices will help you at all.

While I know for a fact that the manufacturers don’t give us the very best that they come up with (their designs are subject to cost and mass production), I’m pretty sure that in these days of car companies reporting huge losses, they would most certainly use any amazing new technology they found to boost gas mileage.  While big oil does have its fingers in a lot of places, and I’m sure there’s some mutual back-rubbing going on, I think Ford would much rather double their MPG and have every single person wanting to buy one, than stick to status quo and keep losing sales in order to appease the oil companies. If there were a cheap device out there that could reliably provide these amazing gains, I’m pretty sure we’d see them (possibly toned down some) from an OEM before too long.

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