J runners

First, there are two shape of ports...they will differ on the head side of the runner.
1.) Rounder Port
2.) Oval Port

but, for the most part the Motor Generation we list in here will work. The exception is the J37a1 which has oval ports (newer style oval), where all the other Gen 1 and Gen 2 motors have round. Then you get into the new J37 dual Vtec (ZDX, RLX, etc) and they have a single piece runner setup. Outside those, as long as you stay within the motor Generation you'll be fine.