Monday, July 21, 2008

With Smart Driving Comes Great Savings

Gas-Saving Tips for the Savvy Consumer - Sakina Rangwala & Amy Adkins @ Washington Post

As I've continued to modify my car I've placed engine efficiency at the top of my list when considering a new part purchase. The last two parts I bought were a shorter shift lever and a new diverter valve for the closed loop turbocharger. I don't have a large engine (1.8l with the turbo that produces only 170hp at stock, but probably a little more now) so the engine is rather efficient as it is. But there are ways of improving the engine's output and thus reducing the amount of fuel needed to keep it turning at certain speeds. Aside from the regular maintence there are other things one can do to improve engine, drivetrain and overall performance of nearly any consumer vehicle.
Rangwala has compiled a list of practices and ideas that can improve fuel economy along with a few misconceptions or dangerous practices one should avoid. Overall, she's put together a decent list that most drivers can follow without drastically changing the way they drive. I do have two items that I think Rangwala has gotten partially wrong. The first is the air filter. While your air filter does need replacing at regular intervals, a new air filter alone will not give you any noticeable fuel savings. But replacing the whole air intake box with a cold air intake will. As Rangwala noted, modern cars come equiped with an air intake sensor called the Mass Air Filter that typically sits right off the air box and measures the temperature and volume of air entering the car. The car's computer, or ECU, adjusts the amount of fuel entering the combustion chamber so the proper fuel-air mixture is reached. A cold air intake is designed to lower the temperature of the incoming air. Cooler air is denser and the denser the air the more you can put into the combustion chamber. The MAF and the ECU will compensate for the change in air volume and temperature by adding more fuel to the mixture. While it sounds like you would use more fuel you actually end up using less as the engine has a more efficient combustion driving the pistons. A five to ten percent increase in fuel economy is common with the replacement of the stock air intake. The cost of aftermarket cold air intakes can run between $150 and $400 but considering the price of fuel it's a worthwhile investment.
The other item Rangwala muddles a bit is the one on fuel additives. I think she should have differentiated between so-called 'octane boosters' and fuel system cleaners. Boosting octane doesn't do a damn thing for your car, particularly one that's built to take a certain octane of fuel in the first place. In point of fact, raising the octane in a car that's not designed for higher octanes can actually damage the engine. The other item, the fuel system cleaner, does help your car. By keeping the fuel system free of debris and cleaning the intake valves you end up with a smoother running engine. Of course, using a fuel system cleaner also will require that you stick to a strict oil change schedule. Some of the debris in the system gets burned off into the exhaust while some of it gets cycled into the oil system. It's not a big deal to do and the payoff is significant, even if you don't notice it.
The other items Rangwala lists are all pretty good, even if some are just plain common sense ideas. Planning your route, keeping the load in the car light, maintaining proper tire pressure and all of that are things everyone can easily do. I keep coming back to a line I read on a tuning site: you don't see fat race car drivers. Even your own weight can have an effect on fuel consumption. Weight reduction allows several other advantages beyond lessening the strain on the engine. A lighter car is a more nimble car. It is also a car that can take better advantage of serious coasting and light hypermiling. It's harder to do in an automatic-shifting car but taking advantage of downslopes and long stretches to a red light by putting the car in neutral offers significant improvement in fuel economy. The basic idea is to put physics and the laws of motion to work for you. A lighter car can coast for a long time without losing too much of its kinetic energy. Even a slight gradiation in the road can allow you to maintain your speed while letting the engine idle. Done properly you can even come off a downward slope and make it over another slope with little to no use of the engine.
While Rangwala does a decent job of rounding up the most important things a driver should take note of if they want to increase efficiency she ends on something of a sour note. It is true that buying gas in the morning will not increase the amount of gas you get she misses another point about fueling up in the morning that could improve the air quality of a city if enough drivers do it. By refueling in the morning versus after work you save the car from expelling gas vapor into the air. Have enough drivers follow this practice and the overall air quality would see some improvement. This follows with the nature of all the other items Rangwala mentions; they're all common sense ideas that just require a minimal amount of forethought. With gas prices as they are now, I hope drivers start putting that more into consideration.