Originally Posted by semtex

If you compare the photos of the two carefully, it appears that the Berks have two things that the Stillens don't. First, the port for the O2 sensors on the Berks are extended out to make them more resistant to throwing CELs. Secondly, notice that the Berks have a second set of O2 sensor ports built in for hooking up wide-band O2 sensors on a dyno, whereas the Stillens do not. Just making a couple of observations.

Edit: They also appear to yield less gain and are significantly more expensive than Berk. (Sorry Stillen/Josh/Kyle -- you know I love you guys but I have to call it the way I see it.)