I was putting close eyes on my intake manifold while hooking up the vacuum line for my brake booster and noticed that this port appears to have gotten hot enough to blister the paint. The opposite side shows the same blackening and blistering.
Looking at the information I can find online, some heads have this as an open port and some have it blocked off. I initially thought it was a coolant crossover port, but if so I would have expected the other coolant ports to be overheated as well.
Anyone know what this is? I am pulling the distributor soon and did not intend to pull the intake with it, but if this is a problem I want to fix it while I am in the area.
Maybe it is an exhaust crossover? And the previous owner didn't use proper high-temp paint? In which case it is fine, but ugly.
Last edited by Fibonachu; 11/22/20235:40 AM. Reason: added crossover theory
I haven’t seen one of those for years, but I believe they’re exhaust crossover ports for carburetor heat.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
It's a heat riser port that runs exhaust gas under the carburetor during warmup when the flap valve in the exhaust manifold is closed on the passenger's side manifold. It's impossible to keep that area painted- - - -maybe powder coat would work but I doubt it. Make sure the heat riser isn't stuck closed all the time. Jerry
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All carburetor small block factory intake manifolds have the exhaust passage. That passage runs from one head, under the carburetor, to the other head. As HRL noted, it works in conjunction with the exhaust manifold heat riser to heat the intake manifold plenum floor. Depending on year, model, application, the intake manifold gaskets have a changeable restrictor that will tune the amount of exhaust that is allowed to pass through. New intake manifold gasket sets typically include the restrictor and some instructions on the application of the restrictor plate.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
