Correct 86-87 Grand National Intake Manifold to Heater Pipe Fitting Nipple

1KWIKSIX

Well-Known Member
What is the correct intake manifold to Heater pipe fitting?
Some vendors sell this 1/2” MNPT x -10AN fitting with a straight thru large bore of 15/32”, where I’ve read that a restrictor was installed in this fitting from the factory.
Point in case, Racetronix offers a restricted fitting 11/32” opening & restricted ID of 15/64”.
What purpose would the restricted ID fitting provide ?
Obviously would restrict coolant flow to the heater core.
What effect would the increased flow from the larger straight bore on the aftermarket fitting have on coolant temperature ?

Large bore aftermarket nipple is silver & restricted bore Racetronix fitting is black
 

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