TECHNICAL TOPIC: MAXIMIZING YOUR FUEL ECONOMY
DATE WRITTEN: SEPTEMBER 21, 2015
One of the most routine questions we get here at Diesel Power Products relates to maximizing fuel economy. And we can’t blame anyone for asking this, with fuel prices where they are and many of our trucks being daily drivers, getting every last mile per gallon (or maybe gallons per mile) can make a big difference in the pocket book. While each type of truck and its individual uses can sway the recommendations we may give to a particular person, the general philosophies really never change. In order to best explain all of the upgrades we will typically recommend, we have put together an explanation for various product type recommendations, as well as some specific recommendations for numerous vehicle applications.
One of the most common upgrades in any automotive market is that of exhaust. While the majority of consumers upgrade their exhaust for the sound, performance, and general aesthetics of aftermarket exhaust, there are also typically increases in fuel economy, as well. But how can exhaust gain fuel economy? That answer is two-fold. The first reason, is simply due to the increase in power, the engine does not necessarily have to work as hard (as long as you’re not constantly showing off your new exhaust note to everyone), thus less work load is placed on the engine, making it easier for the engine to do its said job. The second reason is due to a decrease in exhaust temperature. Larger diameter, higher flowing exhaust systems assist in extinguishing exhaust and heat away from the engine at a faster rate than the factory exhaust. When we are able to reduce heat (break out your physics books here) that energy is able to be turned into power energy, as opposed to heat energy. Any time you can reduce heat energy and transform that into power energy, the overall efficiency works in your favor to increase not only power, but also fuel economy, basically being more efficient. This isn’t to say we should all put on the largest exhaust we can find, as its a balancing act. If you have too little backpressure on the system, the combustion process will be ill-effected, creating a negative effect because the engine must work harder to make the desired power level again. Overall, most diesels that are either stock or have minimal upgrades can benefit from a four inch exhaust system to outflow the factory system without causing any undesirable results.
CLICK HERE for a recommended exhaust for a CUMMINS
CLICK HERE for a recommended exhaust for a POWERSTROKE
CLICK HERE for a recommended exhaust for a DURAMAX
Diesel engines are kind of like an air pump. They suck air in, compress the air, and push the air back out. If you can supply the cylinders with more, DENSE air, the efficiency of the engine is increased. Dense air can usually be derived from cooler, or cold air, hence the terminology of a cold air intake. Basically, the stock airbox does an adequate job of sucking in air and keeping it relatively cool. However, what most factory airboxes lack are the ability to suck in large volumes of flat, tabulated air. Most current style factory airboxes use a flat, panel filter that limits your physical surface area of incoming air. Secondly, most stock boxes have multiple “mufflers” designed to quiet down the incoming air charge. While these mufflers do an excellent job of quieting down the airflow, they also cause considerable turbulence for the inbound air. Think of an airplane here, when you hit turbulence, the plane loses speed and overall efficiency, as it must work harder to fight through this turbulent air stream. Your engine and turbo are no different. Flat air moves faster, and can be pushed through the engine at a faster rate, and even be compressed more easily. The advantage of most aftermarket cold air intake systems is that they will traditionally feature a larger air filter for additional surface area to suck in air, as well as remove any of these inline muffler systems. The result is a flatter, higher velocity air stream equating to faster throttle response, cooler temperatures, better overall horsepower, and even higher fuel economy.
CLICK HERE for a recommended intake for a CUMMINS
CLICK HERE for a recommended intake for a POWERSTROKE
CLICK HERE for a recommended intake for a DURAMAX
Most people have heard the terms “chip,” or “tuner,” or “programmer,” but what are these and how do they actually increase fuel economy? Simply put, what is most commonly referred to as a “chip” is an electronic device that plugs inline to at least one sensor or input on an engine to alter the signals before they are sent to the vehicle’s computer (ECM). An example of a popular “chip” would be an Edge Juice with Attitude for a 2006-2007 Ram Cummins. This chip will plug into the MAP (Manifold Absolute Pressure), rail pressure sensor, as well as several other inputs and alter the signal before the ECM reads these signals to enhance the mechanical functions of the engine.
Next, what most people refer to as either a “tuner” or “programmer” describes a device that is designed to store and upload a file to your vehicle’s ECM, essentially changing the factory programming of the vehicle. In most cases, tuners or programmers plug into the vehicle’s OBDII (On-Board Diagnostic) port located under the dash, and once programming is complete, you can store the device back in its case, as many are not permanently mounted in the vehicle. Several popular examples of this type of device are EFILive, MADS Electronics Smarty tuners, and BullyDog GT tuners.
While most diesel owners would typically install some type of tuning device for added horsepower, there are also fuel economy advantages in most cases. The big advantage to any of the above mentioned methods of tuning are that they usually feature multiple levels of programming, and one of these is most often a fuel economy mode. From the factory, the programming is extremely one dimensional, designed to suit the masses. However, there are definite gains that can be had when retuning the computer specifically for added fuel economy that can start delivering a very noticeable reduction in your stops to the fuel station. By altering timing, injection duration, rail pressure, and simply overall engine mapping, you will not only pick up some MPG’s, but even a noticeable gain in power…pretty hard to find any negatives there!
CLICK HERE for a recommended tuner for a CUMMINS
CLICK HERE for a recommended exhaust for a POWERSTROKE
CLICK HERE for a recommended tuner for a DURAMAX
Yes, these two items are directly related to one another! Most trucks come from the factory with roughly a 3.73 type of ring and pinion ratio and 31-33” tall tires. This tire to gearing ratio is very well rounded for the majority of people that do a little towing, a fair amount of commuting, and, in general, use their truck for most everything. Many trucks have options for both higher and lower gear ratios, as well. For years, most diesels could have a lower 4.10 gear ratio that is well suited for individuals that tow more frequently. Further, we are beginning to see more auto manufacturers offering higher gear ratios, such as a 3.23, that is a great alternative for those not towing as heavy and looking to lower their engine RPM for increased fuel economy.
But, if you’re anything like us at Diesel Power Products, stock tires only serve one purpose, to be turned into a tire swing. A term we throw around a lot here is “40’s are the new 35,” think it’ll catch on? So, as you can guess, we run fairly large tires that can have a dramatic impact on the driving characteristics of a truck. In the simplest of theories, installing larger tires will reduce your speed to RPM ratio, thus should increase your fuel economy, right? WRONG! Two issues arise with this fallacy: weight and engine load. Most larger tires, especially mud terrains, are drastically heavier than their stock counter parts. This additional load causes more strain on the engine to physically turn the tires, making it work harder, causing a decrease in fuel economy. Secondly, as a ballpark average, increasing the tire size larger than a 35 inch diameter with roughly a 3.73 gear ratio will make the engine physically work harder, again, decreasing the fuel economy. So, how do you still look cool and not kill your MPG’s? First, do your homework on tires and find some that aren’t filled with lead weights. Its surprising how much weight you can shave on similarly sized tires by shopping around based upon the weight.
Secondly, especially if you are going to run larger than a 35 inch tire, you need to lower the gear ratio if running some of the previously mentioned higher factory ratios. This will bring the speed to RPM ratio back in check. If you are unsure of what gear ratio is best for you, its pretty simple math to bring the overall run out back to factory specifications. Let’s use the common factory 265-70R-17 sized tire with a 3.73 ring and pinion ratio as an example. If you’re bumping up to a 37 inch tire and want the speed to RPM ratio to be close to the same as factory, the first thing you need to do is convert the P-Metric tire to a good old, easy to read diameter measurement in inches. The easiest way to do this is to whip out the trusty tape measure, but if you don’t have the stock tires any longer, you can always do an online search for “tire size calculator” which will bring up exactly 1.2 zillion hits. This tire size results in a 31.6” measurement, however, different brands of tires can vary slightly in their physical measurement. Using some cross multiplication, we then punch in the following equation:
3.73/31.6 = X/37
This will tell us that for an equal run out, we want to install a 4.37 gear ratio, but no one makes that exact ratio. At this point, a decision would need to be made to either go with a 4.10 or a 4.56, as these are the most common ratios in that range, however, some aftermarket manufacturers are beginning to release some in-between ring and pinion sizes that would be a better, more exact match. Overall, properly matching up the vehicle’s use, tire size, and gear ratio can not only impact the fuel economy, but drastically effect the driving manners of the truck by increasing turbo spool up time, lowering EGT’s, and having proper shift patterns on automatic transmission equipped trucks.
CLICK HERE for a recommended ring and pinion package for a CUMMINS
CLICK HERE for a recommended ring and pinion package for a POWERSTROKE
CLICK HERE for a recommended ring and pinion package for a DURAMAX
Attention Dodge owners, do you ever wonder what those guys driving SuperDuty’s are doing out in the cold on a snowy morning huddled near their front wheels? No, they’re not giving their tires a pep talk to get them through the snow, they are locking their hubs. That’s right, they have to get out of their truck, and manually lock their hubs before engaging the four wheel drive. You may think that your Ram does all of this automatically, and if you do, you’re unfortunately incorrect. Heavy Duty Rams’ hubs are constantly engaged, meaning they are constantly spinning, heating up, and wearing out, where a SuperDuty must have its hubs engaged when the driver wants to put the truck into four wheel drive.
Ultimately, each method has its own perks, but from a fuel economy stand point, braving the elements to manually lock your hubs is of advantage. As mentioned, SuperDuty’s do this from the factory, but Ram owners have the option of upgrading to a mechanical locking hub from such companies as Dynatrac, Spyntec, and Yukon. Will it ever pay for itself in fuel economy gains? Yes, but not necessarily quickly. Most Rams will average a two mile per gallon fuel economy increase with the conversion. Based upon that information, and that the average price for a conversion kit is $1700, and using a price tag of $4.00 per gallon of fuel, it would take roughly 85,000 miles for it to pay for itself, assuming you do not have to pay for the installation. Combine this with easier steering and stronger components that will last considerably longer than the stock parts, and you have a good argument for upgrading.
CLICK HERE for a recommended mechanical locking hub conversion for a CUMMINS
If you can recall way back in 2007, you probably noticed new labeling at the diesel pumps mentioning something to the effect of ULSD (Ultra Low Sulfur Diesel), 15 ppm sulfur content, designed exclusively for use in diesel vehicles produced in and after 2007, and so forth, so what was all that about? In short, new mandates were set to produce cleaner diesel fuel, as well as cleaner burning diesel engines. The ULSD was to be limited to 15 parts per million of sulfur, down from the previous LSD (Low Sulfur Diesel) at a whopping 500 ppm. With this change in sulfur content also came a host of changes to the fuel quality, as well. The most tangible difference for most diesel owners was the reduction in the cetane rating of the new fuel. The original LSD fuel carried a cetane rating of typically around 50, where ULSD is in the 40-45 range based upon numerous studies that have been conducted to randomly test cetane ratings across the country. This means that diesels built pre-2007, which were designed to run on 50 cetane point fuel, were now forced to run fuel ten points lower than originally intended. Obviously, this degrade in the cetane number affects the overall combustion performance of the fuel, meaning that there was a slight horsepower and fuel economy loss across the board. For vehicles built 2007 and after, these diesels have merely always dealt with the lower rating, but would surely gain power from the higher cetane rating, but would soon become clogged with deposits in the emissions systems due to the higher sulfur content of standard LSD.
So, how do you get the cetane number back up, but without shoving 33 times the sulfur into the engine? The answer is simple, fuel additives! There are a plethora of diesel specific additives on the market that perform numerous tasks ranging from incremental cetane increases, water separation, fuel stabilization, gel point reduction, increased lubrication, and with any combination of the previously mentioned. But since we’re talking about increasing fuel economy, the most important factor is cetane. Most fuel additives that combine a cetane increase with one of the other benefits will actually raise the cetane number between one and three points. While this is definitely advantageous, especially when combined with the other benefits of anti-gel, water separation, and so forth, the biggest gain in fuel economy comes when we get a larger cetane increase, such as with Fuel Bomb’s Hellfire blend. Hellfire will increase the cetane number eight points with the addition of only four ounces of additive to a standard sized fuel tank. At this point, it will take trucks back to the LSD cetane rating, but with the lower sulfur content, a complete win-win!
CLICK HERE for more information on F-Bomb Diesel Additive
Water methanol injection systems are kits designed to inject highly pressurized fluid directly into your intake manifold to aid in both cooling the intake charge, as well as increasing the efficiency of the fuel’s burn in the cylinders. The timing and duration of the charges are based upon numerous factors, such as boost, load, and throttle position, depending on the brand and type of system. Basically, the water portion of the mixture will aid in cooling the air, which as most know, equates to denser air, and dense air creates a better combustion. The methanol is responsible for increasing the “burn efficiency” of the diesel fuel, meaning that more of the existing fuel is burnt. When more of the existing fuel is turned into power energy, as opposed to heat energy, you gain both power and fuel economy.
Now, the surprising part is that many people actually use washer fluid as their injectable! Completely out of coincidence, many high end washer fluids contain roughly the same chemical composition as purpose built water methanol that is designed to be injected into an engine’s intake system. This doesn’t mean you can pick up the cheapest fluid off the shelf at your local parts counter, but there are many brands that can be utilized, which is why some people will even use their factory washer fluid bottle as their holding reservoir, making it a dual purpose tank under the hood, as opposed to mounting a separate tank elsewhere on the vehicle.
But how much fuel economy can really be gained? We quite often receive feedback from customers that their average fuel economy increased two miles per gallon. Of course, you now have the added cost of purchasing the water methanol mixture, but with that factored in, the increased fuel economy and power, and lower exhaust gas temperatures, adding a water methanol system is a great addition to almost any diesel vehicle.
All of the late model “Big Three” diesels feature what are known as High Pressure Common Rail (HPCR) fuel systems that utilize a single injection pump that turns the low pressure fuel from the tank into a high pressure stream of fuel capable of pressures in excess of 30,000 psi. For years, the standard type of pump used was coined a CP3, a very capable, long lasting pump design by the professionals at Bosch. Over the last several years, however, we have begun to see the emergence of a new breed of high pressure pump, called CP4’s, that have proven themselves as not having the overall capabilities as the previous CP3. As power adding devices are installed on the truck, the fuel delivery requirements are typically increased, taxing the CP4. This can result in a less-than-desired amount of rail pressure, producing improperly performing injectors.
In order to remedy fluctuating CP4’s, and even CP3’s, we recommend installing a second injection pump to not only eliminate fluctuations, but also decrease the load on the single pump, resulting in a longer service life. Overall, the benefits are a more reliable truck that will gain fuel economy, power, and the potential for a ton of power that will come from other power adders without starving the injectors of fuel.
Your injectors are the final step in the fueling process before your liquid fuel is transformed into energy, so it only makes sense that these are a vital part of the equation when investigating ways to produce additional fuel economy, as well as power. There are several factors relating to your injectors that can effect the overall efficiency potential of your truck. First and foremost, the general health of your injectors can be a large contributing factor to your current fuel economy. In short, injectors are designed to spray fuel out of numerous microscopic orifices to create a pattern that is in direct relation to the design of the piston bowl. As injectors become worn, this pattern is altered which will negatively effect the combustion within the cylinders, causing a reduction in efficiency. Thus, by replacing your worn injectors with new or properly remanufactured units, your fuel economy can be restored.
Now for those with properly functioning injectors, you still have a great potential for increased fuel economy by installing a set of upgraded injectors. There are many factors that can attribute to increased MPG’s and power from upgraded injectors, so we will give you a few examples. First, many manufacturers slightly modify the spray angle and even increase the amount of orifices, but reduce the overall size of each orifice in order to increase the atomization of the fuel, causing a more complete burn. And the more complete the burn, the more efficient the engine is. Another good example would be that of the factory injector found in 1999-2003 Ford Powerstrokes. These models of 7.3L’s ran what is known as a split shot injector that actually shoots a small amount of fuel at pre-ignition in order to quiet the engine down. However, by changing these out to a single shot injector that only has one main injection event, as what is found in the earlier 1994-1997 model years, fuel economy can be picked up, as well as power. And finally, upgraded aftermarket injectors almost always increase the overall power of the truck in varying increments. If you are careful with your selection and do not select an injector with too large of a displacement, you will add fuel economy simply because the truck has more power to get the same job done. Just think of a stage coach with three horses pulling it versus eight horses. Those eight horses can go a heck of a lot further without stopping to rest because each one is not having to work quite as hard. But remember, the only way this tactic works is by ensuring your foot is not constantly in the “go pedal” enjoying your newfound additional horsepower!
We are definitely not a posterchild for aerodynamics with a large portion of our fleet running 40” or larger tires, however, aerodynamics can definitely play a large role in increasing fuel economy. One addition we like to install that does not disservice the general use of most any truck is that of a roll up tonneau cover. These install in a matter of minutes and can be rolled nearly completely out of the way for loading items in the bed or hooking up to a fifth wheel or gooseneck trailer. But when you’re cruising without a full bed, you can decrease your drag coefficient, reducing friction, equating to better fuel economy.
And for those that have ever followed MythBusters, you’ll understand how simply removing or dropping your tailgate will actually increase your drag coefficient as it kills the air mass that would usually be circulating in the bed. Now, instead of the air stream flowing evenly over the cab and past the bed area, it becomes a jumbled mess. The addition of a tonneau cover keeps a linear air flow, still improving on aerodynamics over no bed cover, without the added weight of a fiberglass canopy.
CLICK HERE for a recommended tonneau cover for a CUMMINS
Every ounce of weight that is added to the truck will make it that much more difficult for the engine to complete its job, common physics here. While much of the weight we add to our trucks is somewhat unpreventable, such as service bodies, ladder racks, et cetera, any unnecessary items should be left behind when attempting to maximize fuel economy. Further, when looking at various upgrades and upfits, do some research on the material and thickness of materials being used. For instance, if you’re going to outfit your truck with a flat bed, aluminum beds are becoming much more prolific and offer up an extreme reduction in weight in comparison to steel. And if you’re going to be building your own bed, do you really need ¼” thick side skirts on your service body? Probably not. Leave the thicker material where the abuse will be occurring, but go thinner where you don’t need the additional protection.
(Insert a motherly figure wagging her finger at you)
We don’t need to preach about ensuring you’ve done all of your regular service work to include fluid changes and valve adjustments, but one thing to seriously consider is switching all of your oils to a full synthetic blend. Yes, we realize that synthetic is more expensive than standard dinosaur oil, but for good reason. Think of it this way: standard oil is produced by harvesting oil from the ground and removing anything from it you don’t want, where synthetic is made from the ground up to PUT IN everything you DO want. Quality full synthetic oils will outlast standard oils meaning that they can be ran in the vehicle substantially longer, negating the cost difference in the grand scheme of things. Further, these oils do not break down when exposed to prolonged, excessive heat, as dinosaur oil does, meaning you’ll get better protection for all of your vital engine and drivetrain components. And how does it effect fuel economy you ask? That answer is simple: by having an oil with increased lubricity, less friction is created, meaning the parts can move more easily, requiring less driving force to keep those parts moving.
CLICK HERE to see our recommendations for proper LUBRICANTS
Now that you’ve taken our recommendations and installed all of the previously mentioned products onto your truck, are you going to get 40 miles per gallon? Not likely. The honest truth is that the more fuel economy adding products that are added to the truck, the less of an impact each one makes. That being said, all of the products mentioned have ancillary benefits besides fuel economy. Some add horsepower, some add reliability, so you can rest assured that even if you don’t add an additional twenty miles to the gallon, the truck will perform better than it ever did, and be built to take a beating for years to come.