The longer, smaller and more bends a tube has the more restriction. Air is restricted [no matter how slightly] by the side of tubing[correlated with length], directional change and width.
Lets start with width as it ties into most everything else. Lets replace air with water as its flow characteristics are smiler. Trying to pass a X amount of water through a tube of X width will take a certain amount of time. That time will decrease as the width of the tube gets bigger up to a point. [1]When the tube is big enough the time it takes for the water to flow through will level off and stop increasing. This is the optimum size. Big enough to allow said amount of water to flow through but not clumsy or oversize.
The sides of tubing also restrict flow. Air is rubbing against the sides causing friction the friction restricts flow. The rougher the side of the tube is and more perpendicular groves [slits, imperfections etc] are to the flow the more restriction you will get. Longer tubes cause more restriction and less flow. If the tube is really long it will even cause a lag in the time that outside air gets to where it needs to.
Directional change is more obvious. anything changing direction will slow down to some degree it is all depending on the severity of the direction change.
Now with all this said it may seem like a hot air intake is the way to go, short tube, no direction change and only TB width to worry about. BUT their is one major factor we must include.
Colder air is more dense and therefore more can fit in a defined space. Think of why we drop pulleys we want an optimal amount of air to be inducted into the engine.
With that being said a a FWI seems like the best choice which is the opposite of the above logic. It takes the air from outside the engine bay where the air is virtually ambient.
So whats really the best? Experiments need to be conducted to measure the optimal volume of air that the engine takes in under different rpm's while keeping the ambient air a constant. Then different HAI's, CAI's And FWI's need to be tested to see which provides with the volume it needs closest to the optimal a measured above. Then the IAT's need to be tested to see what induction method runs closest to the optimal temperature. Different materials have to be taken into consideration also as heat soak is a big problem with different applications. The intake that provides the engine with the most volume and the coldest air wins.
So who wants to run the tests any takers? There are countless setups and countless intakes made. The combinations are endless. WHats the best for a stock Gp may not be so for even a slightly modded one.
Moral of the story, no one has/will test every setup AND intake and never will. This is most likely because it is not that big of a deal. Differences in HAI's, CAI's and FWI's are made apparent upon testing and the differences between products of the same nature are so trivial it doesn't even matter.
Still have to add my opinion, i feel if the wizaired drops temps to near ambient [even after running the vehicle for lengths of time] as some people claim then that's the way to go. Cant get colder then ambient [without an i/c, spray etc.] On the same hand if the FWI's give an optimal amount of volume then that's the way to go [Remember 1]. If you are running an intercooler and your IAT's are optimal then a HAI is the way to go.
Originally Posted by Bio248
