[GoreMaker]

I'm planning out the re-assembly of the coolant lines on my 77 Trans Am 400/4-spd with factory AC. My engine build has KRE D-port heads and I'm running hoses from the back of the heads to the water crossover at the front. The passenger side rear fitting is teed to connect a 5/8" hose that goes to the heater core, like the factory setup.

Based on what I'm seeing in the service manual, my car did not come with a vacuum-actuated cutoff valve for that line. There doesn't appear to be a provision in my climate controls for such a vacuum line so I'm inclined to think that's accurate.

My current setup in that area has no flow restriction going to the heater core, but I'm pretty sure the factory nipple that was pressed into the rear of the cast iron head had a built-in restrictor spring. Even the nipple that KRE provides for that location has zero flow restriction. It seems like my current setup would pull unrestricted hot coolant from the back of the right head and send it through the heater core and then into the suction side of the water pump, thereby pre-heating the cooled coolant from the radiator all the time. Should I be adding a flow restrictor to the line that goes to the heater core? What kind of flow rate should I be aiming for in that line?

[78w72]

there is no vac actuated cutoff valve on these cars of this era. im not sure where or how they restricted coolant flow but probably in the head outlet like you mentioned.

on my E-head motor i used a threaded AN fitting that steps down to a smaller outlet size based on the size of AN hose used, i think i used -10 for the heater outlet, but the outlet hole on the fitting is smaller than the inlet size of the heater core tube. to reduce the inlet hole size/flow a little more i also used a stainless washer in the hose at the inlet of the heater core, cant recall the exact size but it was just big enough to match the OD size of the inlet tube but the center hole was maybe 3/8"-1/2". not sure if that matches the factory reduction size but it definitely reduces the amount of coolant flow into teh heater core & has been working fine for 6+ years now with lots of high rpm drag strip & street time.