Baffle or what on factory 340 intake?

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dibbons

dibbons

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Purchased a second hand factory 1972 four-barrel (Thermoquad) intake manifold. I notice on the underside there are two threaded holes. It that for a heat shield to keep oil off the bottom of the manifold? That would get hot there anyway because of the exhaust heat crossover passage, wouldn't it? Thank you.
 
There are a couple of different intake valley pans in the aftermarket.
 
weld up the holes and get a set of metal intake gaskets that seal off the crossover and disable the exhaust manifold flapper in the open position. Cooler manifold, denser mixture, better performance, etc.
 
dibbons said:
Purchased a second hand factory 1972 four-barrel (Thermoquad) intake manifold..
Click to expand...

While you are diddlin' with that, look down in the manifold. If it's a 72, it should have the EGR "floor jets." That year did not have an external EGR valve, but it DID have jets drilled between the intake plenum and the heat crossover, creating a constant exhaust leak into the intake

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Del, that's actually for the 1973 340. The 1972 intakes had bumps in the primary floor. The 1971 was completely flat.
 
I see the jets in the bottom of the intake plenum, not sure if they are open any longer though. If I block the heat crossover passage, I guess it really won't matter.
 
dibbons said:
I see the jets in the bottom of the intake plenum, not sure if they are open any longer though. If I block the heat crossover passage, I guess it really won't matter.
Click to expand...

Then it is a late 72 casting (for 73) or a 73 casting. Same intake as the prior ones. It may flow a tad less, but you caint prove it by me. It's a fine piece. Use it.
 
You can also just put pipe plugs where the floor jets are. I wouldn't sweat the heat shield myself. More chance for it to come lose, which is worse than oil coking to the bottom of the intake.
 
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