E-Mail “How Can I Make My Car More Efficient?”

February 26th, 2012
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I get the strangest e-mails sometimes.  In guess people think I just have the answers to everything.   Here’s one:

Dear Depleted Cranium

The price of gas keeps going up but I can’t afford a new car and I really just want to figure out if there’s a way to make my car run more efficiently and burn less fuel. It would be nice if it made the performance better too.   I really am more interested in saving gas. I keep seeing all these products that go onto the gas line or the air filter or somehow are connected electrically.  I keep hearing that they are scams.  They sound too good to be true, so probably are.

Is there something that is not a scan that will boost my cars fuel mileage?

The internal combustion engine is a mature technology that has been tweaked and tinkered with for many years. The car business is cutthroat so manufacturers are trying to make their engines as efficient as possible. If there was a simple device like a magnet you could slap on to make the car burn fuel better it would come standard. A few more miles per gallon is a big deal in the automotive industry, especially at today’s fuel prices.

That said, there are a few things that could potentially improve the fuel efficiency of a car and also boost performance, but not by a huge amount:

  1. Keep the car well maintained and tuned – In a new car this is not going to make any difference, but as time goes on, spark plugs wear out, potentially resulting in less perfect ignition.   Fuel injectors can get dirty and oil degrades.   Just keep the car in good repair and it will provide the best fuel economy possible.  Check the owners manual to see how often you should bring it in for a tune-up.   Also keep the tires properly inflated.  But don’t expect any of this to make that big a difference.  Unless the car is in pretty bad need of maintenance, it won’t make a noticeable difference.
  2. Add a cold air intake – I am a little hesitant to suggest this, because in my experience it really does not produce any improvement you’ll notice, but at least in principle, if you can get the intake air temperature cooler, it will improve overall engine efficiency.   Most engines take in air under the hood where it’s already pretty hot.  A good cold air intake sucks in air from an area where it has not been preheated much by the engine.   It also should not restrict the flow of air by much, since that makes the engine work harder.   I’d recommend against putting one in if you don’t know what you’re doing, because improper installation can cause a lot of problems, some of which could ruin your engine.  And in any case, don’t expect this to make more than a very modest difference.
  3. Upgrade to a low resistance exhaust system – The exhaust system you choose for your car never will improve the performance of the engine directly.  An engine will always do best if it has no exhaust system at all, and just vents out the gas directly from the exhaust manifold.  That would be very loud and dirty, however, and modern regulations require a catalytic converter.  Pushing the exhaust through the piping, the catalytic converter and the muffler makes the engine do a little extra work.  Therefore, if you install an exhaust system with less resistance, such as larger pipes and a less restrictive muffler, it can result in the engine generating slightly more horsepower from the same amount of fuel.  Again, don’t expect anything major from this.   Most people who put performance mufflers on their car really just want it to sound loud and obnoxious.   Making the exhaust system actually as low resistance as possible requires completely rebuilding it, which is expensive and probably not worth the modest savings you’ll get.
  4. Modify the ECM Code – I am again hesitant to include this one, because usually it’s more trouble than it’s worth. Modern cars have an electronic engine control module which can often be modified by using a programer or by replacing the original ECM with one that is modified with new firmware. Most car manufacturers code their ECM to provide the best compromise between fuel economy, performance, engine response and so on. In some cases, it’s possible to gain more of one of these by making trade offs on the others. For example, some modifiers can squeeze a tiny bit more power out of their engine by sacrificing fuel economy. It’s also possible that you could make the engine use a little bit less fuel if you tweak it to rev up a bit slower or change other aspects of the engine. I don’t really recommend this, especially if you’re not sure of what you’re doing, and because you will ultimately end up having to make tradeoffs somewhere, since the manufacturer already does a pretty good job of balancing performance, fuel economy, reliability, response and so on.
  5. Add a turbocharger – This is probably the one thing that can actually result in a major increase in performance and overall efficiency to an internal combustion engine.  It uses a turbine, powered by the exhaust flow of the car, to spin another turbine that compresses the intake air before it reaches the engine.  Because the engine gets more air, it can operate more efficiently.  This will almost always produce better performance.   It may also improve gas mileage, but that really depends on the engine and how you tune it.   You will definitely need to reprogram the engine controller if the engine did not come with a turbo charger.There may be complications.  Not all engines can take the added compression, the additional compression may require you use higher octane fuel in the engine, which would defeat any potential savings and the turbocharger can be difficult to install depending on the car.  Turbochargers get very hot and therefore may need additional cooling components.  Installing them requires re-routing the engines exhaust and intake air.  It’s a complex job and not all engines provide a good place to locate the turbocharger.Turbochargers are expensive, especially when you factor in professional installation, which is required unless you really know what you are doing.  They may or may not actually result in a noticeable improvement in mileage.  When they do, it’s still not generally going to result in enough savings to pay for the cost of installation.  For this reason, turbochargers are generally installed for performance reasons but not to provide improved fuel economy, at least not in gasoline engines.

I’m sorry but that’s pretty much it. Aside from other basic things like trying to accelerate gradually and not gun the engine too much, avoiding any unnecessary items mounted to the outside of the car, which may increase drag and things like that, those are really the only things you can do and they probably won’t help enough to make them worth the effort, with the exception of keeping the car well maintained, which is always a good idea anyway.


This entry was posted on Sunday, February 26th, 2012 at 2:30 pm and is filed under Good Science, Misc. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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58 Responses to “E-Mail “How Can I Make My Car More Efficient?””

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  1. 1
    brian Says:

    There are a few other things you can do. If you drive mainly stop and go in the city keeping weight down will help so empty the trunk and don’t keep a full tank all the time. If you drive mainly on the highway then reducing wind resistance will help, sadly the easiest and possibly only way to do this is to drive slower.

    The best way is to drive less if that’s possible. Plan and combine trips, walk, take the bus, ride a bike etc…


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  2. 2
    MikeC Says:

    Driving style is probably the greatest effect – be aware of what is happening ahead of you – start coasting before a red light or stop rather than driving right up to it and braking hard, accelerate gently, always drive in the highest gear that is able to handle the speed (I prefer manuals), don’t accelerate up hill, coast downhill.

    I can eak out another 50 km from the 65 l tank of my BMW 323 by doing this more often than not, or another 20-30 km from the 30 l tank of my my little 1.3l mid-90′s shopping trolley!


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  3. 3
    MikeC Says:

    And something else I overlooked – tyre pressures.

    Running low tyre pressure means the car is doing more work than it should deforming the sidewalls – more work = more gas. And running high tyre pressures results in less area on the ground which can mean increased wear and less grip = more slippage – good for making smoke, not so good fur keeping costs down!


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  4. 4
    DV82XL Says:

    Buy a car with a manual transmission, and learn to use it properly. By coincidence both my wife and I own Honda Accord Coupes of the same year (2001) and engine size, both bought secondhand four years ago, eight months apart. One is standard, the other automatic, the only other difference being the color. The manual always gets better mileage, as both of use have owned more manuals than automatics over the years.

    But one must drive it properly, leaving it in lower gears long enough before shifting to really see the benefits. Where a manual really shines is in the Winter in low traction situations, as one can keep the ratio at the ideal setting for the road conditions.


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  5. 5
    drbuzz0 Says:

    All good ideas, but let me stress that this e-mail was asking how he could modify his car or what product he could add. Hence “buy a new car” is not really within the realm of possibilities. I mention driving style.

    I think he was more getting at the question of things like “magnetic fuel saver” – nope, nothing like that actually works. There are things you could add to an ICE and I mention the ones I can think of, but there are limits.

    About the only thing that is really going to make a big difference is a turbo charger. And as mentioned, adding a turbo charger to an existing car just for fuel economy makes no sense.

    I’ve considered adding a turbo charger or supercharger to my car (and ultimately decided against it because of the engine layout) as a way of giving it a little extra kick, but the cost is never going to be recouped in fuel savings, if there are any fuel savings at all, which there might not be.


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  6. 6
    DV82XL Says:

            drbuzz0 said:

    I’ve considered adding a turbo charger or supercharger to my car (and ultimately decided against it because of the engine layout) as a way of giving it a little extra kick, but the cost is never going to be recouped in fuel savings, if there are any fuel savings at all, which there might not be.

    I strongly doubt that a turbocharger will improve fuel economy in any case, as the function of these units is to supply more air to the intake manifold to permit more fuel to be burned. There may be some power bands where the engine is sipping less fuel per unit torque, but in new cars the ECM should be taking care of any situations where that would happen anyway.

    Superchargers are even worse. Because they are spun by a direst connection to the engine crankshaft, they add a net load to the engine, lowering fuel economy even farther. Turbochargers at least (if properly designed and installed) recover wasted energy in the form of heat from the exhaust to compress the air.

    Ether way, as you approach max volumetric efficiency, mileage per unit volume of fuel will start to drop, because you cannot get more energy out than you put in.


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  7. 7
    drbuzz0 Says:

            DV82XL said:

    I strongly doubt that a turbocharger will improve fuel economy in any case, as the function of these units is to supply more air to the intake manifold to permit more fuel to be burned. There may be some power bands where the engine is sipping less fuel per unit torque, but in new cars the ECM should be taking care of any situations where that would happen anyway.

    Superchargers are even worse. Because they are spun by a direst connection to the engine crankshaft, they add a net load to the engine, lowering fuel economy even farther. Turbochargers at least (if properly designed and installed) recover wasted energy in the form of heat from the exhaust to compress the air.

    Ether way, as you approach max volumetric efficiency, mileage per unit volume of fuel will start to drop, because you cannot get more energy out than you put in.

    I am sure a supercharger would not improve fuel efficiency. As for turbochargers, I have heard different accounts on that. I know that when the engine is designed and built to incorporate the turbocharger it can be optimized to produce a lot of power from an otherwise smaller engine displacement, thus resulting in higher fuel economy than you would get from an engine of comparable output with natural aspiration.

    I’ve seen turbo chargers billed as being able to improve fuel economy.

    I think the claim is, at best, questionable. I don’t think it’s impossible, but I doubt you’d get much in a stock engine that is engineered for natural respiration.


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  8. 8
    Anon Says:

    I’ll just suggest http://www.fuelsaving.info/ as pretty much the resource on this topic (other than changing your driving style there basically is nothing you can do to get better fuel economy, though using public transport or walking are also viable).

    The way that turbos are used these days to reduce fuel consumption is that they allow a smaller engine to be used to provide the same performance, that’s pretty much only something that can be done with new cars (a turbo engine will pretty much always have higher fuel consumption than a non-turbo of the same displacement).


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  9. 9
    DV82XL Says:

    Well that’s a bit of a marketing fudge. The key phrase is, “otherwise smaller engine displacement,” which is true, but misses the point. Gas consumption must be compared between engines of the same size in this case, for the metric to mean anything.

    At any rate within the context of a bolt-on modification on an existing engine, particularly a modern one already equipped with fuel injection and computerized fuel/air control, I would be very surprised to see any net improvement in mileage.

    One thing that was tried for a few years in aviation before the advent of turbine engines, was so-called compound supercharging. In this strange setup, a compressor was attached to the crankshaft ahead of the cylinders feeding the intake manifold, and an independent turbine, attached to the crankshaft behind driven by the exhaust manifold. Properly set up the turbine not only overcame the load of the compressor, but added several tens of percent power to the engine proper, thus resulting in much higher fuel efficiency.

    The only ones I ever saw were a Lockheed Super Constellation with engines made by Alison that had this feature. This was many years ago when I first started, but the old guys were very familiar with these and claimed they were popular in their day.


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  10. 10
    Will Says:

    “Upgrade to a low resistance exhaust system – The exhaust system you choose for your car never will improve the performance of the engine directly. An engine will always do best if it has no exhaust system at all, and just vents out the gas directly from the exhaust manifold. “

    Completely false. Exhaust scavenging and proper tuned length will do wonders for low and mid-range performance. At these rpm ranges, the already moving fluid from one cylinder will help pull exhaust from another (hence “scavenging”). In fact, having an exhaust system without enough back pressure can often be worse than a system of the proper length but slightly too restrictive mufflers. Plenty of performance charts from Dynamometers will provide evidence to the severe and noticeable loss of mid-range power from drag pipes (straight exhaust with no muffler). The only time one would want no (or completely unrestricted) exhaust is if one is running a dragster and only cares about power at a small range at high RPM, otherwise overall engine efficiency goes to hell. I just wanted to point that out since we are talking about efficiency and not peak power across 1000 rpm band.


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  11. 11
    MikeC Says:

    AFAIK the reason turbochargers are useful is that it enables you to get the same horsepower for a smaller and hence lighter engine- any fuel saving comes from the weight saving.

    Way back before electronics we (young fella’s) used to do things like port & polish heads to get smoother airflows, balance pistons, etc – working in aircraft maintenance meant I had the tools & connections to get these done for free – you wouldn’t want to spend the money on your family sedan!! And of course het objective was more horsepower – but it is also true that they would enable the car to use less power on the “housekeeping” tasks of moving air around.

    Compound-turbochargers were a few years before my time – and right at the limit of piston engine technology!! :)


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  12. 12
    Will Says:

    I am also skeptical of a turbo making an engine more efficient. It will certainly allow an engine to produce more power and when it is spun down the engine can still be fairly economical. My contention is turbochargers add a significant amount of heat to the incoming air charge. Most of this heat is usually (but not always) removed with an inter-cooler. If the stetup is aftermarket and has no inter-cooler then the engine is working with an air charge at a much lower density than normal which will reduce efficiency. The air received from an inter-cooler will still be hotter than if it was just pulled from under the hood and considerably hotter than most cool air intakes. I haven’t run any numbers but it doesn’t seem logical that these factors would increase efficiency AND performance. At best I would think cautious driving would produce near stock mileage while a heavy foot delivers lots of fun at terrible fuel efficiencies. Perhaps I’m off base, I’d love to hear from anyone with some design expertise in forced automotive induction.


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  13. 13
    Anon Says:

            DV82XL said:

    Well that’s a bit of a marketing fudge. The key phrase is, “otherwise smaller engine displacement,” which is true, but misses the point. Gas consumption must be compared between engines of the same size in this case, for the metric to mean anything.

    If you’re looking for a new car then you car more about fuel consumption per unit of power/torque and if the smaller turbo can produce the same power would consider it equivalent to the larger NA engine.

            DV82XL said:

    One thing that was tried for a few years in aviation before the advent of turbine engines, was so-called compound supercharging. In this strange setup, a compressor was attached to the crankshaft ahead of the cylinders feeding the intake manifold, and an independent turbine, attached to the crankshaft behind driven by the exhaust manifold. Properly set up the turbine not only overcame the load of the compressor, but added several tens of percent power to the engine proper, thus resulting in much higher fuel efficiency.

    The only ones I ever saw were a Lockheed Super Constellation with engines made by Alison that had this feature. This was many years ago when I first started, but the old guys were very familiar with these and claimed they were popular in their day.

    It was actually a Wright engine, reliability though was a bit of a problem with them (mechanics called the power recovery turbines, parts recovery turbines for some reason). Some others tried it but only Wright got it to mass production.


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  14. 14
    DV82XL Says:

    I stand corrected it was the Wright R-3350 Duplex-Cyclone engines in an ex-TCA Super Connie that I saw. However I seem to remember that the turbine unit itself was made by Alison, but I may be wrong.

    They were nicknamed ‘parts recovery turbines’ because of the low MTBF these units had. Apparently they were a maintenance nightmare.


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  15. 15
    drbuzz0 Says:

    I have heard of engines on aircraft with a “power recovery turbine” which is like half a turbocharger. The energy from the exhaust stream is used in its own right not to power an intake turbine. The idea is that if properly designed it recovers more power than is lost from the obstruction to exhaust.

    Apparently this idea has been revived to some extent for automobiles, where some have suggested that it would result in lesser parasitic load on the engine to have exhaust gasses drive a turbine to run the alternator then to have it belt-driven. I doubt any savings would amount to much.

    Some diesel engines have been built with blowdown turbines as well.

    http://en.wikipedia.org/wiki/Turbo-compound_engine


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  16. 16
    Dave Says:

    Can you really increase the performance of a car by changing the engine software? I have heard this but always doubted it a little.


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  17. 17
    drbuzz0 Says:

            Dave said:

    Can you really increase the performance of a car by changing the engine software? I have heard this but always doubted it a little.

    It often can be done but that does not mean you would want to. On my car, for example, it’s possible to hack the firmware to make the engine output more power, but the hack involves changing how it manages the exhaust gas return and the fuel injection. Normally the engine is tuned to burn all or nearly all the fuel, but basically what you can do to get more power involves making it run rich. The engine can produce more power when running rich.

    There are problems with this, of course. First, it hurts fuel economy quite a bit, because some of the fuel just goes out the tailpipe. It also is a violation of the emissions laws in most sates. You are also are making the engine run outside its design specs, which has the potential to cause unexpected damage or problems.


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  18. 18
    DV82XL Says:

            Dave said:

    Can you really increase the performance of a car by changing the engine software? I have heard this but always doubted it a little.

    You can change the performance parameters but its’s a give and take deal,; what you gain in one area, you lose in another. Often higher power, for example, comes at the cost of increased pollution, increased gas millage, at the cost of acceleration, and so on. In many jurisdictions it is outright illegal to tamper with the engine software.


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  19. 19
    Anon Says:

    You can get better performance by changing the ECU mapping but for stock engines the chips are oversold (if you’ve modified the engine then you’ll probably need a new ECU mapping to actually take full advantage of it).

    Of course you’ve still got to meet emissions regulations (many of the things done to increase power will prevent that). For fuel economy you could probably get a significant improvement by running the engine somewhat lean but that increases NOx emissions so it’s illegal.


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  20. 20
    Robert Sneddon Says:

            DV82XL said:

    One thing that was tried for a few years in aviation before the advent of turbine engines, was so-called compound supercharging.

    The main reason supercharging was implemented on piston aircraft engines was to make them work efficiently at higher altitudes. Eventually towards the end of WWII piston-engined bombers and fighters were flying at 30,000 feet plus where the air pressure is only 30% of sea-level. Supercharging also meant the engines had an improved power-to-weight ratio which was an important factor in obtaining better performance from the same airframe weight.

    Really, as someone else said, if there was a magic magnet or other gadget that would improve fuel consumption then manufacturers would be using it already. The most basic factor which might increase fuel consumption day to day is low tire (ObUKEnglish: tyre) pressure and that’s totally in the control of the car owner. Remember President Obama’s comments about this and how he was howled down by the Right who took to waving tire pressure gauges at him? He was correct and they were wrong.


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  21. 21
    Amoeba Says:

    One approach has been hinted-at. Reducing weight, or rather mass. Remove the carpets, anything in the trunk that you don’t need, unused seats.


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  22. 22
    Sigivald Says:

    0. Ensure that the tires are properly inflated. That’s huge.

    (As you and Mr. Sneddon mentioned, naturally. But it’s so huge it should be an item by itself; it’s free or nearly free and can literally make a 4 or 5% difference in mileage, all with a little bit of attention every few weeks.)

    0b. Drive smoothly, accelerate as gently as is compatible with not-being-a-dick-to-fellow-drivers, stop smartly. Rapid throttle changes and acceleration waste fuel, if that’s your big concern*. (MikeC said that, but I’m also going to repeat it, because it’s one of the few things you can actually DO to get noticeably better fuel economy.)

    (* I drive my ancient car Like I Stole It, but this has very little effect on its economy as it’s horribly inefficient to begin with [76 HP and 21 mpg from a 3500# sedan], plus it prevents carbon buildup. This is not an issue for people not driving 35+ year old diesels, typically.)

    There’s no technological magic bullet, as others have said.

    Well, there are lots of them, but they’re all far more expensive than it’s worth; there’s no point in spending $4000 on an engine swap to save $150 a year on fuel for a car you’re not going to be driving for 40 years!

    Likewise serious body work can decrease the coefficient of drag, which is huge – but also both insanely expensive as a modification and usually ass-ugly.

    On ECUs, unless you’re driving a sports car it’s probably already tuned for economy more than power, so that’s pretty marginal.


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  23. 23
    Joe Says:

    Ok regarding turbo charging to reduce fuel consumption. They absolutely CAN do that, but the circumstances that are being talked about here, as an add on, it won’t or usually won’t.

    A turbo charger is powered by exhaust gas pressure. By having the turbo charger, some power must go to the charger that requires the engine work harder to push out the exhaust gas and therefore is a load on the engine, but some of the power is lost anyway, so it can recover more power than it otherwise consumes. The turbo charger then forces air into the intake, and this reduces the engines burden on the intake cycle. Basically it is pushing more air which helps and it is restricting exhaust flow, which hurts, but it can be made so that it helps more than it hurts by recovering wasted power and putting it back into the engine.

    The engine can be further tuned to take better advantage of the air flow from the turbo, especially in diesel engines where getting high compression is important. Turbo means the engine does not need to work as hard to get the necessary compression. It can help in gas engines too, but maybe not to the same extent.

    The reason this will never work in the circumstance discussed above, where you are bolting on a turbo is that aftermarket turbo chargers are never designed to achieve maximum efficiency and nobody installs and tunes the engine to get maximum efficiency. The turbos on big diesel engines are tuned for getting the best efficiency and that might be true on some OEM – equipped turbo cars too. Turbo chargers sold after market are purely performance upgrades and are never designed to have the maximum increase in power and that usually means they work best at higher RPM versus cruising and they are also usually intended to give as much boost as possible versus have the low exhaust restriction.

    It would never make sense to upgrade a passenger car with a turbo system to try to save gas because the expense of turbocharging a vehicle is too high for the savings to ever balance it out.


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  24. 24
    I'mnotreallyhere Says:

            DV82XL said:

    Well that’s a bit of a marketing fudge. The key phrase is, “otherwise smaller engine displacement,” which is true, but misses the point. Gas consumption must be compared between engines of the same size in this case, for the metric to mean anything.

    Bovine faeces – the comparison worth making is for engines of comparable performance.

    Although I’d like to stress to those who don’t know that :
    1) Brake Horsepower (BHP) for an engine varies throughout the rev-range, but the figure you’ll always get told is the maximum value, even if this isn’t very relevant to 99% of users.
    2) Engine designers *do* get told by their managers to push up the max BHP at the expense of useful performance in everyday life – and because they’re basically all car/motorcycle enthusiasts they tend to hate it.

    Depending on the car, I’d guess the automatic gearbox, if you have one, is either controlled by the ECU or it’s own electronics, tweaking that to change the shift points may allow better performance by making it behave more economically.

    But all of that is expensive and highly technical. The cheaper option is simply to attempt to strip out any and all excess weight in the car. Remove seats if you’re not going to use them, especially if they can be easily unbolted and later reattached. The aggressive can strip out carpets, inner door panels, the ceiling, most of the ventilation system, rear electric window motors if you’ve got no passengers (or seats!) in the back, the list goes on.

    Ricardo, who are a pretty solid engine design consultancy with a lot of expertise in downsizing engines (smaller displacement but turbocharged), did a study for an aluminium consortium on the impact of weight reduction (and engine downsizing) on fuel consumption (linked below). The bottom line for those who’re lazy is that a 5% reduction in weight should give you a percent or two in fuel economy – variable by car type and use cycle.

    Some might say that 5% weight for 2% economy isn’t a lot and they’re right – but you’d change your savings account for 2% more interest and plenty of people put more money into fuel for their car than into their savings account.

    http://aluminumintransportation.org/downloads/AluminumNow/Ricardo%20Study_with%20cover.pdf

    P.S. If you feel like trying a fitness regime to lose some weight, the extra fuel economy is a pretty tenuous argument (unless you’re massive!), but everyone’s got to start somewhere!


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  25. 25
    DV82XL Says:

            I’mnotreallyhere said:

    Bovine faeces – the comparison worth making is for engines of comparable performance!

    I fail to see your point. Are you disputing the fact that for a given displacement, fuel economy will be less for an engine with a compressor on the intake manifold? Because the whole point of putting a blower on an ICE is to provide more air to permit more fuel to be burned. Yes, similar performance can be had at smaller displacements, but that was not the crux of the argument.

    In real-world driving the presence of a turbocharger will not result in a net saving in fuel per distance traveled, and in the case of stop-and-go driving will be less due to the lag that will be present as the unit spools up at each start. While those cars that have this feature built in may have some compensation programmed in to the ECU firmware, I doubt that in the case of a bolt-on (which is being considered here) that this would be so.


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  26. 26
    Calli Arcale Says:

            MikeC said:

    And something else I overlooked – tyre pressures.

    Running low tyre pressure means the car is doing more work than it should deforming the sidewalls – more work = more gas. And running high tyre pressures results in less area on the ground which can mean increased wear and less grip = more slippage – good for making smoke, not so good fur keeping costs down!

    Different tires will also make a difference; there are low-resistance tires available, and as there is less drag, you will get better economy. However, that’s not always a good thing — first, tires aren’t cheap, and second, a 3 MPG improvement is not worth risking an accident due to increased stopping distance. More to the point, the increased wear will reduce the life of the tires, which could well defeat the purpose of improving the mileage; that’s exactly what I found out when I tried doing that. It did improve my mileage, but I had to replace the tires more quickly. I replaced them last November, and have kept them at the recommended inflation ever since.


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  27. 27
    I'mnotreallyhere Says:

            DV82XL said:

    I fail to see your point. Are you disputing the fact that for a given displacement, fuel economy will be less for an engine with a compressor on the intake manifold?

    No – though I suppose you might be able to get a gain in stupidly extreme rich-running engines, but that’s a daft avenue to go down.

            DV82XL said:

    Because the whole point of putting a blower on an ICE is to provide more air to permit more fuel to be burned. Yes, similar performance can be had at smaller displacements,

    This was my point, and as such it’s daft to say “Gas consumption must be compared between engines of the same size in this case, for the metric to mean anything.” – we don’t measure the utility of our car in terms of the fuel used, it’s not the objective. The objective is to get from point A to point B, via road network C applying road rules D avoiding idiot drivers E though to Y whilst carrying load Z.

            DV82XL said:

    but that was not the crux of the argument.

    It wasn’t perhaps the crux of the original email, though replacing the entire engine is potentially a wiser idea than getting an after-market turbo and inter-cooler fitted – but heavily dependent on availability.


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  28. 28
    DV82XL Says:

    Yes, suppose if you take what I wrote out of the context I intended and place them in one of your own they might appear stupid….


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  29. 29
    josh Says:

    My mpg is an obsession since my car of six months has it displayed right on the dashboard. It clicked back up to 40.2 this evening. Obviously had a good run on the motorway.

    Attempting to follow the ebb and flow of the congestion not only saves fuel but also time for everyone and a smooth lane is an expedient lane. I always see the outside lane performing worse as it will lock up completely while the lower lanes can keep moving. I attribute this to demographics. The outside lane is most likely to be populated by the kind of driver who has a very inefficient boost n brake style. This leads to instability in the flow and.longer journey times.


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  30. 30
    DV82XL Says:

            josh said:

    My mpg is an obsession since my car of six months has it displayed right on the dashboard.

    That reminds me. Back in the day, one of the most useful bolt-on, if you wanted to save fuel, was a vacuum gauge. If you kept half an eye on it, you could improve fuel economy considerably by being less aggressive on the accelerator, and selecting the right gear, (in a standard) and generally improving your operating habits. I haven’t seen one installed on a car in years, but as Josh wrote, the new integrated mpg indicators can do the job.

    What would be really neat, (IMO) would be some way to have this displayed as the cash value of the fuel you were burning, so you could see the true cost in real time. I’m sure this could be done, but my wife pointed out that she would find such a display so stressful she wouldn’t be able to keep her mind on her driving.


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  31. 31
    Amoeba Says:

    While not technically having any influence on car efficiency, the most fuel efficient transport is not to use the car, but to go by bicycle – one of the most efficient means of transport known. Cycling is two to three times as energy efficient as walking. According to this source, a bicycle is at least 25 times as efficient as a standard petrol car and unlike many other modes, it is door-to-door transport.
    Sustainable Energy — without the hot air Page 119
    http://www.withouthotair.com/

    Many journeys are easily cycled. In the UK 50% of journeys are 7 miles or less. So by not using the car on local journeys one avoids the most inefficient journeys.

    In Urban areas it is fairly common for 40% of traffic to be cruising for parking spaces. At certain times, Christmas etc, the percentage of cruisers is much higher. All this unnecessary driving wastes fuel.

    Remember, by cycling you make the world a better place. No noise, pollution and cycling makes one healthier and feel good too.


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  32. 32
    matthew Says:

            Amoeba said:

    While not technically having any influence on car efficiency, the most fuel efficient transport is not to use the car, but to go by bicycle – one of the most efficient means of transport known. Cycling is two to three times as energy efficient as walking. According to this source, a bicycle is at least 25 times as efficient as a standard petrol car and unlike many other modes, it is door-to-door transport.
    Sustainable Energy — without the hot air Page 119
    http://www.withouthotair.com/

    Many journeys are easily cycled. In the UK 50% of journeys are 7 miles or less. So by not using the car on local journeys one avoids the most inefficient journeys.

    In Urban areas it is fairly common for 40% of traffic to be cruising for parking spaces. At certain times, Christmas etc, the percentage of cruisers is much higher. All this unnecessary driving wastes fuel.

    Remember, by cycling you make the world a better place. No noise, pollution and cycling makes one healthier and feel good too.

    Efficient, possibly. Practical, not so much. Try taking 2 kids to school or hauling a week’s worth of groceries by bike.

    I’ve said it before, and I’ll say it again – any form of transport where you can’t haul 2 kids, hockey equipment, and a load of groceries can’t be the be-all and end-all of transport.


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  33. 33
    Amoeba Says:

            matthew said:

    Efficient, possibly. Practical, not so much. Try taking 2 kids to school or hauling a week’s worth of groceries by bike.

    I’ve said it before, and I’ll say it again – any form of transport where you can’t haul 2 kids, hockey equipment, and a load of groceries can’t be the be-all and end-all of transport.

    You are of course entirely wrong. It’s a common mistake to believe the myth that a car is the be-all and end-all of transport.

    There are many people who do not rely upon a car for everyday load-carrying and it’s a growing trend.
    Example bikes
    http://clevercycles.com/blog/products/bicycles/family-cargo/
    Note: my only connection with this company is limited to viewing their website.

    People will eventually realise that driving in cities is essentially harmful to society – antisocial, and that driving is subsidised by society. Drivers need to realise that is becoming increasingly unacceptable and that they must pay the full costs of driving.

    A study that covers part of the external costs. There are numerous others.
    http://www.ce.utexas.edu/prof/kockelman/public_html/trb08vehicleexternalities.pdf

    The external costs of free parking:
    The High Cost of Free Parking – Shoup
    http://www.uctc.net/papers/351.pdf


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  34. 34
    Anon Says:

    Yes, some people manage to live their whole lives with only a bicycle, some people manage to live their whole lives without running water as well, doesn’t mean we should follow them.

            Amoeba said:

    There are many people who do not rely upon a car for everyday load-carrying and it’s a growing trend.

    Yeah, people who live in inner city areas with good public transport.


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  35. 35
    drbuzz0 Says:

            Amoeba said:

    You are of course entirely wrong. It’s a common mistake to believe the myth that a car is the be-all and end-all of transport.

    There are many people who do not rely upon a car for everyday load-carrying and it’s a growing trend.
    Example bikes
    http://clevercycles.com/blog/products/bicycles/family-cargo/
    Note: my only connection with this company is limited to viewing their website.

    Might work for some. Would not work for me.

            Amoeba said:

    People will eventually realise that driving in cities is essentially harmful to society – antisocial, and that driving is subsidised by society. Drivers need to realise that is becoming increasingly unacceptable and that they must pay the full costs of driving.

    Does not matter if it is harmful to society. It is beneficial to ME or to the other individual who is using the car. Not driving will not benefit society. It might if everyone did, but that kind of thing never makes people do anything because there’s diffusion of responsibility.

    Sorry but I love my car and you could take away free parking and make gasoline twice the cost and I wouldn’t drive any less. I don’t think I’m alone in that regard.


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  36. 36
    Edis Says:

    There is very little that can be done to improve the milage of a car without significant changes which will end up costing more than you save on gas.

    The best tip to save on gas is to drive in a way that reduce the fuel consumption. To keep the tires correctly inflated are also a good tip, this is also important for road safety. There are also low viscosity low friction oils than can be used, but make sure they are suitable for your specific engine. Of course, you should also remove any unnecessary equipment in or on the car which adds weight and drag.

    As for cold air intakes, most cars already take air from outside the engine bay (in front of the radiator is common source for cold high pressure air). But cold air isn’t always better for efficiency as the lower temperature might hurt vaporisation.

    A turbocharger also won’t reduce the fuel consumption of a car. The purpose of turbocharging is to allow downsizing without reduced performance. By turbocharging a car manufacturer might select smaller turbocharged engine instead of a larger naturally aspiranted engine, both offering the same performance since the smaller engine is turbocharged. The smaller engine will be more efficient for daily driving since operates at a higher average bmep at part load. The key here is that engine efficiency increase with increased load.

    There is little that can be done to save fuel by modifying the software in the ECU without it having some sort of negative impact. This can be increased stress on the engine, increased emissions or the need to use a more expensive higher octane fuel.

    With a naturally aspiranted engine you can’t do much to improve the performance of the engine by software alone unless the stock engine is restricted to use its full potential. Today all mondern ECUs operate with a torque demand strategy. The position of the gas pedal is translated to a torque request, and this torque request is used to calculate an airmass/combustion request. This airmass/combustion request is used to control the throttle valve of the engine (diesels use fuelmass/combustion requests instead). So if a manufacturer makes two versions of an engine, with say 140 and 170 hp, these two engines can use the exact same hardware the only difference being that the less powerful engine have a lower set maximum torque request. If that’s the case you can increase the perfomance quite a lot with software only. With a turbocharged engine you can also allow a higher boost pressure to increase the airmass/combustion.

    Increased spark advance can also increase output and efficiency up to a point. But increased spark advance also increase cylinder pressures and can cause knock. The latter might demand the use of a higher octane fuel. With a naturally aspiranted engine however, the engine usually use spark advance for Maximum Brake Torque from the factory, and going beyond this will do nothing.

    Running richer will only reduce engine output. Normally an engine run richer than what is best for output alone at high load, the limiting factor here tends to be exhaust temperature. At lower load the engine is operated at lambda 1 to allow the catalyst to both oxidize and reduce pollutants.

    Since an engine spends most time at part load at low engine speed a less restrictive exhaust system will do very little to save fuel, you certainly won’t get your money back on buying the new exhaust system to begin with.

    When it comes to exhaust systems any backpressure is really more than you would like to have, but here’s the thing: a large incorrectly tuned exhaust system can actually increase backpressure at certain speeds at the moment when the exhaust valve is about to close, which is the critical moment. This can significantly hurt performance. All exhaust systems are designed to improve engine volumetric efficiency by pulse tuning. When the exhaust valve opens a pressure pulse forms in the exhaust port. This pulse travels downstream the pipe in the manifold and when it reaches an area increase it will be reflected as an expansion pulse and travel back to the exhaust port. Correctly tuned this expansion pulse will arrive at the exhaust port at the time the exhaust valve is about to close.

    Some heavy truck engines are equipped with turbocompound, in principle a second turbine connected to the crankshaft after the regular turbocharger, but for a passenger car it’s not worth the added cost. These are also known as blowdown turbines and are usually worth a few percent of the total shaft power. Blowdown refers to the period when the exhaust valve have been opened and the exhaust flows out from the cylinder due to the high pressure, something which occur late during the expansion stroke. There are a few NACA papers on the subject that can be downloaded from NASA’s website.

    Old turbocharged WW2 engines where often both turbocharged and supercharged, the turbocharger being used to compensate for the lack of airpressure at high altitude. The reduced airpressure at high altitude also increased turbine performance.


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  37. 37
    Russ Says:

    Simple way to make an ICE more efficient: Force it to run lean. Basically cut back how much fuel goes in to the available air.

    they don’t make them that way because it causes you other problems. It can damage the engine because the fuel has lubricating properties. It can cause it to stall out more frequently. It will cause power loss. IT might not start cold.

    It can increase emissions too, because the engine will be more prone to missfires and NOx and CO might go up too. For this reason changing the fuel-air ratio to any degree that can do this is probably going to be illegal anyway.


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  38. 38
    Anon Says:

    CO and unburned hydrocarbons would tend to go down when running lean and NOx will also go down but the catalytic converter won’t be able to deal with that NOx so you’ll end up with higher emissions.

    Lean burn can be used in direct injection engines without causing massive amounts of pollution but that’s only relevant if you’re buying a new car (which will come from the factory set up for it), modifying your engine to run lean will almost certainly put you in violation of anti-pollution laws (such modifications are specifically banned in the US for example).

    http://www.fuelsaving.info/air_bleed.htm has quite a bit more detail on lean-burn.


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  39. 39
    Russ Says:

            Anon said:

    CO and unburned hydrocarbons would tend to go down when running lean and NOx will also go down but the catalytic converter won’t be able to deal with that NOx so you’ll end up with higher emissions.

    Lean burn can be used in direct injection engines without causing massive amounts of pollution but that’s only relevant if you’re buying a new car (which will come from the factory set up for it), modifying your engine to run lean will almost certainly put you in violation of anti-pollution laws (such modifications are specifically banned in the US for example).

    http://www.fuelsaving.info/air_bleed.htm has quite a bit more detail on lean-burn.

    I am not an expert, but according to some things I’ve read, some people have modified the engine to run so lean that it gets missfires, where not all the cylendar strokes are igniting as they should. This will obviously cause some major emissions problems. It can also damage the engine if you do it badly enough.


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  40. 40
    Anon Says:

            Russ said:

    I am not an expert, but according to some things I’ve read, some people have modified the engine to run so lean that it gets missfires, where not all the cylendar strokes are igniting as they should.

    This will obviously cause some major emissions problems. It can also damage the engine if you do it badly enough.

    If it isn’t igniting then that’ll cause massive unburned hydrocarbon emissions (and unleaded petrol has a high aromatic content).

    Of course if you’re getting large amounts of unburned hydrocarbons coming out your exhaust pipe it means your engine is wasting some fuel, well maintained engines shouldn’t be wasting any more than a percent or so but if leaned it out sufficiently to get misfires I wouldn’t be surprised if it is actually increasing fuel consumption.


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  41. 41
    DWMF Says:

    Change all lubrications around the car regularly. Keep a very close eye on the color of the main engine oil. If it goes darker than strong tea (with milk), change it with clean oil. If your car has an autobox, also do the same with the ATF, it should stay pink like a rose wine. If it gets dark red or brown, change the ATF for clean, making sure that the torque converter is also well cleaned (with new ATF).

    Modern cars tend not to need much attention to their axles and bearings. But my experience of older cars instilled the habit of getting the car up on the ramp for close inspection, and if necessary sticking my grease gun on its nipples. [Ooooerr!]

    While it’s up there, give the underside and wheel arches a thorough clean. Losing the mud and crud can only help. Reapply Waxoyl (rust prevention) where it has been washed or worn away.

    Also, keep the old girl clean and tidy. It helps to keep value and cuts down on unnecessary weight. TTFN.


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  42. 42
    Calli Arcale Says:

            josh said:

    Attempting to follow the ebb and flow of the congestion not only saves fuel but also time for everyone and a smooth lane is an expedient lane. I always see the outside lane performing worse as it will lock up completely while the lower lanes can keep moving. I attribute this to demographics. The outside lane is most likely to be populated by the kind of driver who has a very inefficient boost n brake style. This leads to instability in the flow and.longer journey times.

    It’s not demographics; it’s reaction time. On the freeway, the outside lane is where most of the traffic enters and exits. Sometimes, better training on proper merging etiquette would help; in other cases, it’s down to poor design of the freeway entrance. In general, if I’m on a three-lane half of a freeway going through the metro area, I prefer the middle lane if I’m going any significant distance, to avoid all the people getting on an getting off. This is especially true in Bloomington, MN on I-494. There are some ugly entrances through there.


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  43. 43
    drbuzz0 Says:

    While many of the suggestions here for keeping the car maintained, avoiding unnecessary heavy loads in the trunk, maintaining good tire pressure and so on are valid, I think that they miss what the e-mailer is asking for.

    All those steps will only keep the car as efficient as it was to begin with, when it rolled out of the factory. The e-mailer asked for a way to add something that would make the car more fuel efficient than it is to begin with, under OEM specs.

    Unfortunately, there’s no simple way to do that, at least not without some big expense and sacrifices that would pretty much negate the value of any improvement in fuel efficiency.


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  44. 44
    Gordon Says:

    If the goal is to make the car use less fuel than the oem configuration, you could replace the engine with one of smaller displacement or one that is of a newer design and more fuel efficient.

    I know there are some things manufacturers have experimented with to make cars more fuel efficient by recovering more power from the engine, like using a small sterling engine or even a steam engine to put some of the waste heat to work. It works, but it’s too expensive/complex/heavy/cumbersome to make it worthwhile actually putting in a car.


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  45. 45
    Anon Says:

            Gordon said:

    If the goal is to make the car use less fuel than the oem configuration, you could replace the engine with one of smaller displacement or one that is of a newer design and more fuel efficient.

    Though even there a less powerful engine would have to work harder so may not actually use less fuel (it’s common for very small engines to not actually get the fuel saving (and COâ‚‚ emissions as well, in some countries the smaller engined car will receive lower taxes for being ‘greener’ when it isn’t going to do any better than the more powerful one in the real world) you’d expect from the test when used in the real world).

    Though even then a new engine would probably cost more than what you’d save in fuel costs even if it used less fuel in the real world.


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  46. 46
    drbuzz0 Says:

            Anon said:

    Though even there a less powerful engine would have to work harder so may not actually use less fuel (it’s common for very small engines to not actually get the fuel saving (and COâ‚‚ emissions as well, in some countries the smaller engined car will receive lower taxes for being ‘greener’ when it isn’t going to do any better than the more powerful one in the real world) you’d expect from the test when used in the real world).

    Though even then a new engine would probably cost more than what you’d save in fuel costs even if it used less fuel in the real world.

    I think in most cases, it’s probably possible to find an engine that will preform better in your vehicle, at least if money is not an object, that is.

    my car is a few years old. The engine in it is pretty good, but certainly not the absolute state of the art for the best efficiency you can get. In the past few years, the maker, Chrysler, has come out with a redesigned engine that squeezes a bit more fuel efficiency out. I basically have the LH series of DOHC engines at 2.7 liters. They now are using V-6 engines of the new Pentastar family, which is similar but has some redesigns. The new design does not use an EGR valve and has a different design to the camshafts and the intake.

    It’s slightly better fuel wise. If I re-engined the car I’d probably get better mileage.

    But then again… I’d cost about the same as buying a new car.


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  47. 47
    Anon Says:

    If you’re doing it for fuel efficiency then money definitely will be an object.


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  48. 48
    drbuzz0 Says:

            Anon said:

    If you’re doing it for fuel efficiency then money definitely will be an object.

    Well, if you’re doing it to save money, yes. There is another reason I can think of doing it: Stubbornness and refusal to admit that you can’t do it.

    I’ve been known to succumb to that. Luckily there’s no way I could afford it.

    “Sir, there’s simply no way you could improve the fuel efficiency of this car!”
    “Oh sure I could if I really tried”
    “No. You can’t. You can’t do it.”
    “Oh yeah? You don’t think I can? Well watch me!”

    ….
    $8000 later

    “Check it out. the car now can get 31 mpg. Before I only got 28 mpg. You are wrong! I can do it! I did it”


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  49. 49
    fixx Says:

    “Well that’s a bit of a marketing fudge. The key phrase is, “otherwise smaller engine displacement,” which is true, but misses the point. Gas consumption must be compared between engines of the same size in this case, for the metric to mean anything.”
    - Actually the comparison should be between engines of the same power, which is where supercharging (turbo or crank driven) comes in. With a supercharged engine the power can be the same with a smaller engine. A smaller engine means less weight and better fuel economy. Also turbochargers reduce the pumping losses of an ICE, which is the energy used to move the charge into the cylinders and move the exhaust out.

    A few more things that can be done:

    - Equal length tuned headers with properly sized collectors. All cars should have this but few do. The exhaust scavenging reduces pumping losses.
    - Install an economy camshaft. This one could involve a lot of other changes and involves opening the engine up (so not a bolt on).
    - Small protrusions can be added on the back of the roof before it turns into the rear window. These increase turbulence locally over the rear of the car and change the airflow such that overall wind resistance goes down. You can see these now on some higher end luxury cars. You can copy the shape but proper placement may require a wind tunnel or a bit of trial and error.
    - A car computer that displays your fuel consumption is an excellent way of improving your gas mileage by giving feedback from driving habits and specific speeds at which best economy is achieved. Contrary to popular belief slower is not always better for efficiency. I get better MPG at 90 km/hr than at 80 km/hr in my car.
    - A cheap alternative to a computer is a vacuum gauge. Highest manifold vacuum is generally when you are getting best economy.
    - Low resistance tires.
    - In some cases reducing exhaust or intake restriction can improve performance but this does depend on how the engine is currently configured. It can be done by installing a bigger air filter and/or mufflers with less back pressure. There is a system for performance cars called Supertrap (I think) that allows the exhaust back pressure to be dialed in with plates, this would probably be the best way (also requires free flowing muffler). This mod works best on cars with mass air flow sensors since they actually measure the volume of air entering the engine. This means that induction and exhaust changes will not require remapping of the a/f ratio in the engine computer.
    - Engine oil friction modifiers. These are all those additives you see with all those claims of better mileage and increased engine life.

    Sorry if I’ve repeated ideas already posted, I didn’t have time to read everyone’s comments.


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  50. 50
    Bob Says:

    You can make your car a lot more efficient and even better you cna have it run on water. Why not? Water is part hydrogen and its proven you can run the car on hydrogen. Just fill the tank with water and all you have to do is break that bond and the engine burns the water like it was gasoline.

    Stan Meyers invented a catalyst that does this. It worked great and was about to change the world.

    You know what happened next. The government and the oil company masters and the saudi’s and everyone else who would lose their war fed riches wanted him to stop. They were going to work with Meyers and offered him millions of dollars to shut up about it. He was too honest and would not take it from them, so they moved to plan B and had him killed. RIP Meyers. Genius had uis almost freed.

    People still build their cars to run on water uisng his technology, but nobody goes out and tels the world. I have been thinking of converting my car. Do it for urself and you will be fine, but go out public and they will kill you too!

    http://www.youtube.com/watch?v=WEp6ckvRtj0

    http://www.youtube.com/watch?v=h0dhwlhTs9M&feature=related


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