As someone who's modified cars and made cars pretty fast (I consider 11's pretty fast), an intake will not get you better mileage, at least to no significant degree under most circumstances. If it does it's messing with your AFR. But with modern cars, that won't be the case at light loads. If anyone tells you it gets more, it's probably confirmation bias.
Reasons stated below:
1. No you're not really reducing pumping losses. At least not at partial throttle. Your throttle plate will be the biggest resistrictor.
2. Most factory airboxes are pulling air from an already cool location. You're probably not getting any cooler air then factory. But even if you are say getting a 10 degree reduction, it's probably not enough of a reduction for timing to advance. That air is going through a lot of tubing and a fmic. At low air speed, the temps will be extremely similar. You timing tables will be based upon a TMAP sensor in the intake manifold.
3. So really at light load you are making no more power. You're no more efficient.
4. If you're messing up factory airflow characteristics which can affect MAF or MAP sensors, typically your car operates in closed loop logic during light load. This means that your car will use the wide band O2 sensors in the exhaust, which measures oxygen in the exhaust; and then it will use this information to change air fuel ratio (AFR). It will generally always target 14.7 which will be optimal for catalytic converter efficiency. It does this by trimming fuel with short and long term trims. STFT and LTFT.
5. Now say you do mess up flow characteristics and impart a bias for your MAF or MAP sensory. In open loop you can actually change your AFR. A lot of cars go open loop under heavy load. They ignore the 02 sensor and just base fueling off a MAF or MAP sensory. And you might have actually leaned out AFR from factory. So in this instance you may save fuel. But remember this is when you are driving aggressively or say towing. But if it's leaning out AFR due to sensor biases, then that could potentially be bad and lead to knock and preignition.
Reasons stated below:
1. No you're not really reducing pumping losses. At least not at partial throttle. Your throttle plate will be the biggest resistrictor.
2. Most factory airboxes are pulling air from an already cool location. You're probably not getting any cooler air then factory. But even if you are say getting a 10 degree reduction, it's probably not enough of a reduction for timing to advance. That air is going through a lot of tubing and a fmic. At low air speed, the temps will be extremely similar. You timing tables will be based upon a TMAP sensor in the intake manifold.
3. So really at light load you are making no more power. You're no more efficient.
4. If you're messing up factory airflow characteristics which can affect MAF or MAP sensors, typically your car operates in closed loop logic during light load. This means that your car will use the wide band O2 sensors in the exhaust, which measures oxygen in the exhaust; and then it will use this information to change air fuel ratio (AFR). It will generally always target 14.7 which will be optimal for catalytic converter efficiency. It does this by trimming fuel with short and long term trims. STFT and LTFT.
5. Now say you do mess up flow characteristics and impart a bias for your MAF or MAP sensory. In open loop you can actually change your AFR. A lot of cars go open loop under heavy load. They ignore the 02 sensor and just base fueling off a MAF or MAP sensory. And you might have actually leaned out AFR from factory. So in this instance you may save fuel. But remember this is when you are driving aggressively or say towing. But if it's leaning out AFR due to sensor biases, then that could potentially be bad and lead to knock and preignition.
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