The Maxima has for many years been a do-it-all kind of car. Part family car, part sport sedan, and part everyday cruiser, the Maxima does a little bit of everything a car can do, a little better than most cars. However, fuel economy for this budget sport sedan never has been its strongest suit compared to other cars in its size class. But that situation isn't beyond remedy using some DIY tech, and you don't even necessarily have to look silly doing it.
There's a classic good-news-bad-news situation with this car. The good news is that this generation of Maxima is about as aerodynamic as cars get; even by 1990s standards, you're not going to find too many sedan bodies that are aerodynamically smoother this side of a 1996 Ford Taurus. So, the Maxima body offers a pretty solid foundation, and shouldn't require anything major in terms of external modifications. The bad news is that first, you're not going to find easy improvements through aero, and second, the problem is primarily in the drivetrain. At 17 city and 24 mpg highway, the primary issue here is that the 3.0-liter engine is just putting far more torque to the ground than it needs to in order to move the car. Great for sporty throttle response, bad for fuel economy.
The key to getting the most mileage out of this car is to make the most out of the VG30 engine's excess torque. That means treating the engine like a diesel and keeping rpm as low as possible, which, in turn, means gearing the car down. It is possible to fit a very low 2.44-to-1 final drive gearset; Nissan sells them as replacement parts for this transmission. But that's going to be an incredibly expensive nightmare that will take 60 years of driving to offset in fuel savings. The cheaper route is to use slightly taller tires. Stock tires for this car are 205/65R15, which have a diameter of 25.5 inches and a circumference of 80 inches. Your simplest bet is to swap out for lightweight aftermarket 18-inch rims, and buy a set of economy-car 195/65R18 tires. That will put you at 28 inches diameter, a circumference of 88 inches, and a nine percent effective gain in gearing. For this car, expect that to translate directly into a similar gain in fuel economy.
The problem with fitting taller tires for increased fuel economy is that you raise the car by half the increase in tire diameter -- in this case, about 2.5 inches. That's exactly the opposite direction you want to go if you're trying to save fuel. Lowering springs abound for this car, so you shouldn't have any problem finding a set of springs to drop the car by 2.5 inches to at least offset the gain in height from the tires. The primary issue now is fender clearance. Nissan was kind enough to give this Maxima the tire clearance of a pickup truck, which looks dorky from the factory but works in your favor here. You should just have enough clearance to drop the body down over your tires, and still leave the requisite "two fingers" of clearance for suspension movement. You're going to need stiff springs to keep the tires off the fenders, but the car will handle and look a lot better with those huge rollers filling up the wheel wells.
One the engine, consider the usual battery of bolt-on upgrades. An underdrive pulley set, freer-flowing intake and exhaust, high-flow catalytic converter, upgraded coils and fine-wire iridium spark plugs will all help. A "warm air intake" could make a big difference here, de-rating the powerful engine by sucking hot air from around the rear exhaust manifold and feeding it to the engine. The less-dense air will effectively reduce the engine's displacement and torque output, which is what you need for this application. Some metal ducting from the underside of the manifold to the air cleaner box and a cable-operated butterfly valve will allow you to de-rate the engine on demand, which should pay noticeable dividends around town. The engine's intake air temperature sensor is in the manifold, so the computer will adjust for the increased air temperature if it comes in through the airbox.
If the Maxima has a serious weak spot in its aero profile, it's that blunt nose and the massive clearance between the front bumper and ground. That's going to resist forward movement, and channel air under the very un-aerodynamic bottom of the car. What you really need is an air dam, a flat piece of sheet-metal riveted to the front bumper that fills the gap between the bumper and the ground. But, if you don't want something that looks like it came out of Mad Max, Wings West sells a cool-looking-in-a-1980s-way body kit for this car that utilizes an air dam as close to perfect as you're going to find in 2014. Block off the air dam cooling vents with a clear or black plastic panel mounted from behind the bumper, and you're done. You could finish it off with a flat "belly pan" running under the car, but that might be more trouble than its worth. But between the big wheels filling up those gaping wheel arches, the Wings West body kit and a free-flowing exhaust, you should end up with a fairly economical Maxima that won't embarrass you on the street.
