Intake manifold center port. Closed or open?

Discussion in 'Troubleshooting & Diagnosis' started by brewquest, Jul 12, 2017.

  1. brewquest

    brewquest Member

    Jul 19, 2012
    Denver, Colorado
    Hello all,

    I have a 1970-73 SBC block (id 3970014) and am replacing the intake manifold gaskets. I am replacing them because I have an oil leak out of the china rails. My question is do I close one of the center ports as the instructions say? There was not a cap when I took the manifold off. Pic of instructions below. 1969-72 dont have it closed off. My car is a 1981 and Im not sure what the motor came out of. What does closing off this center port do?

    Also, as a side note I have been struggling with temp issues. (212 degrees f at block by headers.)

  2. Ihada70Z28B4

    Ihada70Z28B4 Veteran Member

    Oct 4, 2002
    Exhaust to EGR and heat crossover to warm the intake for cold weather driveability. I block them off if not driving in cold weather.
  3. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    Nov 4, 2004
    Ringgold, GA
    Do you still have an EGR valve, what intake manifold is on this engine? That crossover and EGR shouldn't be the cause of over heat issues. I don't run them b/c my intake doesn't have EGR or crossover.
  4. 70lt1z28

    70lt1z28 Veteran Member Gold Member

    Oct 3, 1999
    Beavercreek, Ohio, USA
    On pre-egr cars this was to heat the choke bi-metal coil to allow the choke to open faster in cold weather. If you don't have EGR and don't drive in cold weather and don't have a heat riser in the exhaust, then block it. Blocking it will allow the intake to run cooler and that improves fuel charge-density.
  5. brewquest

    brewquest Member

    Jul 19, 2012
    Denver, Colorado
    Perfect, thanks guys!
    I dont have EGR and want it to run cooler!

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