How To Get Into Cars: Hypermiling Mods

While we’re currently in an era of comparatively low gas prices, the last few decades have seen much volatility in the oil market. This can hit the hip pocket hard, particularly for those driving thirstier vehicles. Thankfully, modifications can help squeeze a few extra miles out of each gallon of dinosaur juice if you know what you’re doing.

The art of striving for the best fuel economy is known as hypermiling, and involves a broad spectrum of tricks and techniques to get the most out of a drop of fuel. Let’s dive in to how you can build a more efficient cruiser for getting around town.

Step 1: Know Thine Enemy

The MPGuino is a great solution for monitoring fuel consumption in older cars without a trip computer.

If you want to improve your fuel economy, the first step is to measure it. Without accurate measurement, it’s impossible to quantify any gains made or optimise for the best performance. For those with modern cars, it’s likely that there’s already a trip computer built into the dash. Using this to track your fuel economy is the easiest solution. Instantaneous modes are useful to help improve driving habits, while average modes are great for determining the car’s economy over time.

However, many older vehicles don’t have such features installed as stock. Thankfully, there’s a few ways to work around this. For those driving post-1996 vehicles outfitted with an OBD-II port, tools like Kiwi or Scangauge can often track fuel economy. Failing this, most fuel injected cars can be fitted with a device like the MPGuino that monitors fuel injection to calculate consumption. Fundamentally, all of these tools involve tracking the amount of fuel used per distance travelled. Factory tools and OBD-II gauges do it by using the car’s standard hardware, while the MPGuino splices in to speedometer signals and injector triggers to do the same thing with an Arduino. If you do decide to install a custom device, make sure you calibrate it properly, else your figures won’t bear much resemblance to what’s going on in reality.

Of course, as long as your car has a working odometer and a fuel tank that doesn’t leak, there’s always the pen-and-paper method. Simply reset the trip odometer to zero after filling the tank to the brim. Then, when refilling the tank, fill all the way to the top, and divide the miles driven by the gallons of fuel added back to the tank. This isn’t the most accurate method, as the nature of gas station pumps and automotive fuel tanks mean that tanks aren’t always accurately filled to the brim, due to air pockets and devices used to prevent overfilling. Despite this, it’s a handy way of getting some ballpark figures of your car’s performance over time.

With a good grasp on your car’s fuel numbers, it’s also important to test your mods scientifically. Throwing on some “improvements” and doing a lap of the block while reading the instantaneous MPG readout won’t cut it. Ideally, it’s best to compare several tanks worth of average MPG readings with the car’s established baseline before modification. Routes, grades of fuel, and other factors should be kept as similar as possible if you want the ultimate bragging rights amongst the hypermiling set.

Step 2: Mods

Now that you know what your car is capable of, it’s time to consider modifications to eke a few more yards out of every drop of fuel. The range of modifications vary from the simple and easy to the extreme, with practicality concerns meaning some will be out of reach for the average driver.

Aero – Smooth And Sleek

Despite not looking particularly aerodynamic, the Mercedes A-Class has the lowest coefficient of drag of any production car, Cd=0.22.

One of the biggest areas that can improve fuel economy is improving the aerodynamics of a car. Unlike our previous article, which discussed improving aerodynamics for more grip by increasing downforce, the focus here is to reduce drag. Drag increases with the square of velocity. This means that the faster you travel, the more fuel you need to use to overcome the drag on the vehicle. Mods in this area will have the greatest effect at high speeds, such as during highway driving. It’s important to note that any mods that significantly change the aerodynamic properties of the vehicle may have an adverse affect on handling, so tread carefully. Also, it pays to remember that some vehicles may already have incredibly low drag despite the way they look. For example, it may not appear to be particularly streamlined, but the latest Mercedes A-Class is a leader in low-drag design. Improving on such a design would likely be difficult to impossible without the aid of a windtunnel and 20-30 world-class engineers.

Back in 2008, [basjoos] claimed average MPG numbers in the 70s with this heavily-modified Honda Civic. Note the prominent boat tail and wheel shrouds.

The most basic modifications in this area involve simply smoothing the vehicle’s profile. Taping over cracks, changing out large wing mirrors for smaller, sleeker items, and removing extraneous add-ons like cosmetic wings and large antennas can all make a difference. More serious hypermilers have experimented with blocking off grills, improving fuel economy but risking overheating outside of the coldest days of winter. Using front lips to guide air around the tyres rather than under the body can net some gains, too.

At the more extreme end, body mods can get serious, and seriously impractical. Many hypermilers get deep into structural work with materials like coroplast and aluminium, creating “boat tails” to smooth airflow and reduce MPG. These often compromise the use of rear storage, but can have major effects towards reducing drag. Undertray modifications can also help, at the risk of winding up with your craft project tangled around a driveshaft or suspension arm. Some even go so far as to fit wheel shrouds to further improve their car’s sleek profile.

Weight

The heavier a car is, the more fuel is needed to accelerate that mass up to speed. Thus, reducing a car’s weight is a great way to improve fuel efficiency, with the EPA estimating that removing 100lbs of weight can improve economy by 1-2% on average.

There are plenty of ways to save weight in the average car, particularly for the creatively minded. For example, if you have no friends, there’s no reason to be carrying around all 5 seats in your family wagon. Eliminating the rear bench and front passenger seat can easily save 100 lbs or more, netting a serious gain for precisely zero money. More extreme methods can involve driving without a spare tire, or removing carpets and sound deadening. For the truly dedicated, glass windows can be replaced with lighter lexan panels, and heavy stock wheels can be swapped out for lightweight aftermarket ones.

Tyres

Uneven wear on an overinflated tyre. The pattern of wear shown indicates most of the tyre is contributing no grip, making the car dangerous to drive at any speed.

While not the most exciting modification one can make, tyres nevertheless have a role to play in fuel economy. Overcoming rolling resistance takes fuel, so switching to a lower-rolling resistance tyre can help. For those looking for more, switching to a skinnier tyre than standard can also help, though there are risks here around changing the handling characteristics of the vehicle. Making drastic changes can be dangerous, so often it’s better to lean on the side of caution and just fit a nice set of eco-focused tyres on an appropriately sized wheel.

Additionally, increasing tyre pressure can help. By adding more air to the tyre, it reduces the size of the contact patch. This reduces the rolling resistance, thus improving fuel economy. However, it also reduces grip, and can lead to blowouts and other disastrous consequences. Such measures are even more dangerous in the wet. As a bonus, in modern cars, it will throw all kinds of errors and warnings from your tyre-pressure monitoring system.

Engine

Mazda has spent a small fortune on their unique gasoline compression ignition technology to gain up to 20% improvement in fuel economy. Making gains in engine efficiency is a big-money sport.

The engine is perhaps the hardest place to make significant fuel economy gains as a home gamer. Car companies invest millions of dollars on developing engines, with a strong focus on fuel economy and efficiency. This is an area where cheap one-size-fits-all eBay parts aren’t going to improve on a bespoke designed OEM part. This goes for tuning as well — a day down at your neighbourhood dyno isn’t going to net a more efficient tune than the one Honda spent years testing in all atmospheric conditions imaginable.

This isn’t to say there is never anything left on the table, however. It just requires a very intelligent consideration of the engine as a whole, and a realistic approach to what is possible. One place where manufacturers do have to compromise is price. A budget economy car from the mid-1990s may have a restrictive exhaust, which was chosen for manufacturing cost over outright efficiency. Swapping this out for a better-flowing part may net a few extra horsepower, and allow the engine to breathe more freely, improving efficiency. Oftentimes, a clear look at where costs were cut will find the handful of areas where a stock motor might find a few efficiency gains. However, it can be difficult to make improvements here without spending more than you’ll make back in savings on gas.

Conclusion

Hypermiling is a great way to save a few bucks, but with gas prices at historic lows and electric cars on the market, it’s not the big deal it was perhaps a decade ago. Many now dive into the world of precise driving techniques and advanced modifications not purely for the savings at the pump, but the sheer engineering challenge. While we’re starting to see the sun set on gasoline technology, gains remain to be had, and there will always be hackers looking to wring every last bit of energy out of each drop of gasoline. To those who wrench in pursuit of this goal, we salute you!

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