what is the correct way to install a 1973 pontiac 400 intake manifold?
October 19, 2009 | Car
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Re: “what is the correct way to install a 1973 pontiac 400 intake manifold?”
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That is the heat riser for the bottom of the manifold. If you are not planning a lot of low temperature starts - block it off. It provides heat to the bottom of the intake manifold and allows your thermostatic choke to function properly.
Race pontiacs block it off completely.
If you’ve upgraded to a mechanical or electricl choke - plug the crossover - The cooler the intake manifold the more power you make. The downside is some cold weather driveability until the car comes up to temp. Mine is blocked off on my 73 as I only drive it in the summer. On really cold days its a bit cranky at first but everything is fine when it warms up.
Do not block it off. The block off plates are used in racing applications, keep the fuel/air charge cooler, resulting in about a .1 second faster quarter-mile. Keeping it unblocked will ensure that your engine warms up quicker, and runs better in colder weather. It was unblocked from the factory.
If you live in a cold climate and your choke operates via the heat from the manifold, leave it open. If not, or if you only drive it in warm weather, block the passage. Blocking it will keep your fuel temperature in the carb a little cooler, making the air/fuel charge slightly denser. Either way will not “screw up” your engine. It just might make it take longer to warm up when it’s cold if you block it.
if you are going to drive the car in cold weather do not block it off but if you drive it mostly in the summer go ahead and block it off, all that opening does is heat the carb up faster for winter driving.
I’ve got stainless block off plates set into my intake gaskets to block the heat off from the intake. The fel-pro gaskets with block off option tend to burn out after a few thousand miles. My car runs on the street, and runs fine once I let it warm up.
Be sure the heads and intake are clean and free from old gasket material. Make sure to install the plastic alignment dowels that hold the intake gaskets in place to the heads. I install the gaskets dry, no sealant. Then carefully set the intake down. Dont forget the little rubber washer that goes between the intake and the timing cover bypass hole. Install the bolts but do not tighten them. Install the front long bolt, and pull the intake up to the timing cover with that long bolt. Doesn’t have to be tight, just pretty snug. This keeps the washer from leaking. Now tighten the intake bolts in a criss-cross pattern.