I am using a tight cast aluminum 90 in mine. I have no engineering experience or anything but it seems to me, especially on a big 4" pipe, having a stubby little air filter is going to be more restrictive than a 90* bend with a monster filter. Plus I found this article about airflow through bends with different size piping. It seems to show that a 90* bend such as my 4" cast radiused pipe is only minimally restrictive. In fact, as long as im reading that right, it shows that a smooth 90* bend is one of the most efficient ways to change the direction of airflow. http://www.donaldson.com/en/engine/s...ary/034973.pdf
Who knows...try it out and see if you like it, its just a intake.
