[Soichiro]

So, not being a master mechanic or anything, I bought an aftermarket air filter for the purpose of increasing airflow to the engine, and when I went to install it, I was faced with the question of where to install it. I drive a 2009 Hyundai Elantra, and I discovered that by default, there is a vent at the front of the hood that sucks air directly from outside the car into the engine intake. This normally keeps the intake temp at a constant ~10F above ambient. Well, as the aftermarket filter was larger (and a completely different shape) from the original filter, I had to change this somehow. So, what I ended up doing was removing the original filter and attaching the aftermarket filter, but leaving the pipe that comes in from the outside of the car in the same position, but not attached to the filter. So it looks something like this:

(Lol never mind, I was going to post an image, but I'm not allowed to because I have too few posts!)

Basically, simply by disconnecting the outside vent from the filter, I've disabled the vacuum effect created in the intake valve that caused cold air to be constantly pumped in from outside. So now, when the car is idling, the intake air temp runs at about 25-30F above ambient, but while moving, cold air can still flow into the air filter from outside, so the intake temp remains at about 10-15F above ambient while moving. According to my theory, this should actually be ideal. (I'm not a scientist or anything, but) if I am correct, the time when a warm air intake should benefit an engine the most is at low RPMs--i.e. city driving. This mod accomplishes that. My city MPG average has increased from approximately 26.5 mpg to 31 mpg. Unfortunately I have not yet had an opportunity to test it on highway driving, but if my theory is correct, because the cold air can still flow in while the car is moving, the mod should not have a large impact in either direction on highway driving, which is the intent. I've theorized that a warm air intake can potentially lead to power loss at higher RPMs, so if that is the case, it would be ideal for the air to remain relatively cool for highway driving (although this mod does have the added benefit of keeping the engine compartment slightly cooler during highway driving as well--that may not benefit MPG directly, but it will likely help with durability of engine components and preventing overheating). However, for city driving, this mod so far seems to provide a great benefit.