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How Does Your New Car Get Better MPG Than Your Old One?

Follow Antony

Almost every day we hear of a shiny new car that gets a certain number of miles to the gallon, a number often greater than its predecessor.

It sometimes seems like witchcraft - until significant steps towards high-tech materials are taken, rarely do cars lose weight from one model to the next (with a few honorable exceptions), and weight is generally acknowledged to be an enemy of performance and MPG.

So how are our cars getting not only quicker and safer, but more efficient too? Join us as we explore some of the most common techniques for small mileage gains...

Long gear ratios, more gears

We all know why cars have gears. An internal combustion engine works most efficiently and delivers most of its power and torque at a certain rate. Gears help ensure this efficient power and torque band is utilized as much as possible.

Adding more gears to an automatic or manual transmission means even greater potential for making use of the engine's most effective range, which is why we're seeing ever higher numbers. Long gear ratios allow for cruising at lower engine revs, where the engine is using less fuel. It's a technique used by cars like the 2012 Chevrolet Cruze Eco.

Torque converter lock-up

You'll notice driving an automatic vehicle that engine revs can rise and fall independently of road speed. This is great for smooth driving as the transmission takes up the slack in jerky throttle applications, but it's no good for low-revs, efficient cruising where engine revs can soar or you get a downchange when asking for more power on the freeway.

Earlier lock-up means at cruising speeds a prod on the gas pedal will use more of the engine's low-down torque than high end, gas-guzzling power.

Low-viscosity oils

An internal combustion engine generates a lot of friction. We're quite familiar with friction in cars - it helps us brake. Friction is great for stopping then, but ideally we want an engine to "go" as easily as possible.

As well as advances in tighter tolerances, low-viscosity oils help an engine run with as little friction as possible (while still protecting components). This doesn't just mean more power from energy otherwise lost through friction, but an engine doing less work can use less fuel, too.


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Comments (5)
  1. The lockup torque converter I think I understand. But I have been curious about the DSG transmissions or dual-clutch transmission. Do they even use a torque converter? and how common are DSG transmissions?
     
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  2. DSGs essentially use an electronically-actuated clutch for pulling away (slips it to get moving) and a second clutch that pre-selects gears alternately with the other clutch when on the move. They don't hunt for revs like CVTs and torque converters so they don't need to lock up. It's a bit like driving a manual, but with every gear-shifting process done for you.

    They're quite common in Europe, less so in the U.S. Every Volkswagen Group company now uses them (including SEAT and Skoda) on both gasoline and diesels, Ford has a system (Powershift) as do Renault, Ferrari, Bugatti, Mitsubishi uses one on the Lancer Evo, Nissan on the GT-R and there are almost certainly others.
     
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  3. They can improve economy for many people in the same way modern autos can, but they're usually quite an expensive option.
     
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  4. Thanks for the added information.
     
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  5. @John, not much I can add to Anthony's comments, but I work for a supplier of motors and we supply the motors to a Tier One for the Ford Fiesta and Focus with DCTs (DSGs). Hyundai and Nissan/Renault already use them, too and GM's aren't far away. As transmissions go, they're a little expensive, but not bad, actually, given the usual fuel savings.
    Other common fuel savings methods include turbocharging, electric power steering, start-stop systems, better aerodynamics, direct fuel injection and lighter weight vehicles. Not to mention already common methods such as cylinder deactivation, variable valve timing, and others I'm sure I'm missing now.
     
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