I've got a American turbine At J pump and I've never seen one with a pop off valve ? Is that because most people running triple digits run a Berkley pump ? I'm just curious, I haven't seen any American turbine pumps in race boats before.
if it's an at-309 with the forward slanted hand hole cover, you won't see any popoff's attached to it. there are some used in boats that race, but that suction piece isn't suitable for popoff installation. to use a popoff, the handhole needs to be flat to the boat with more flange area, like a dominator. if your pump is a tj-309, that's an insert pump and wouldn't necessarily be ideal for racing. the sd pump suction pieces come with flanges in place, so the intake has to be set in whatever position will fit the suction piece. looks like a popoff could be used with an sd.
from American turbine, most people are using the dominator 12-s suction piece for racing applications.