Join Date: Jul 2010
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Re: Intake adds better fuel economy?
actually there are 2 sides to this. I don't know if the 1.8 is DI or not but I'm guessing no coz that's an expensive tech and this is a cheap car.
So for a non DI vehicle there are 2 possible outcomes if you modify your intake system.
1. The fuel economy has improved: This is due to an easier breathing intake causing a better atomization of gas, as well as more efficient filling of the combustion chamber. In many cases when you drive the vehicle with the normal intake (if you had a vacuum gauge) you will see a surge in vac and there is a certain amount of drag caused by a restrictive intake system. However this being a 2009/2010 car I would imagine Nissan has done everything in its power to maximize the factory intake efficiency for max mpg. Also a less restrictive intake causes the driver to feel that the car has more power and psychologically he MAY tend to put less throttle input just because of that, causing the ECU to use the fuel map mapped towards a lesser throttle opening, thus reducing the fuel consumption. Logically the only bad thing Nissan COULD have done is to install paper filter to reduce cost, I would be very wary about altering the intake tract or other portions of the intake system prior to the throttle body.
2. The fuel economy has deteriorated: The driver might drive more aggressively because of the added sportiness or sound from the brand new intake. This would be the biggest factor in a sloppier MPG after install. The other possibility is the lack of ram speed due to the freed up intake system, causing fuel to atomize less optimally (again, I'm assuming we have a port injection engine) at the intake valves. This is not the result of a poorly made intake, but rather, an intake designed for a different goal - the ram speed is probably more optimal at higher RPM for its claimed "HP increase" by shifting the ram speed to become more optimal at high volume operations. However, poor atomization of the fuel at lower RPM gives this sense of "losing torque" at lower RPM, causing the driver to press the go pedal deeper in hopes to regain the loss, this would significantly increase fuel consumption as that is going to scale the engine management's fuel map to a higher load/higher performance section.
So it really depends on how the intake system is designed to do. What will be a telltale sign of a good intake system is that you find yourself driving at the same speed with lighter throttle, causing the engine management system to choose a lighter load operation mode.
To be safe it's probably best to just replace the paper filter with a high-flow drop-in unit from an aftermarket manufacturer. That way, you are ensured most optimum Nissan engineering without the cost cutting. Anything more "modified" may or may not help the cause.
What about engines with direct injection? Well the air is always mixed with the fuel before it's released into the combustion chamber as a "packet" of combustible so there will really be no significant difference unless the car is having a hard time breathing through its intake system...