the head bottle necks the oil passages or something. not sure exactly but it will either give half or double the oil press. i forgot what, but the bottom line is it reads funky. mine was kind of a pain in the ass, just do the metric adapter from the oil filter housing (replacing the factory sender), either tee off and still use the factory sender with the aftermarket one or just replace with the aftermarket line or electric sender. i used an a/n line from the metric adapter to the gauge inside the car. you'll need about 20 feet. 16 was veeeerrrrry tight.