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I'm using a 2985 4.9l intake manifold. I plugged the egr hole on the top. Since I'm using headers, the opening on the bottom side of the intake is still open. Do I need to make a block late to close it or is it OK to be left open?
Little late to the party sorry
You can leave it open but as said the factory bolted the exh manifold to the intake and had a valve that would flow hot exh gas to the bottom of the intake.
This heat would keep air fuel mixed where if to cold the fuel would drop out of the air and cause poor running.
At one time you could buy a plate that had 2 pipe nipples that would bolt to the bottom of the intake but as of late I have not seen them.
It is not hard to make using the gasket as a pattern to cut the flat plate. I bought this plate years ago off Ebay.
You just need to watch where the holes come thru
Bolted to the intake manifold. Yes I am using EFI exh manifolds.
Now to tell the truth I think it would do vary little to stop carb icing as the air going into the carb is what would ice the carb so you need to heat the incoming air like the factory did with the factory air filter assy pulling hot air from the tin around the exh manifold.
Yes I am running the factory air filter and Carter v1 carb I do not have the tin on the EFI exh manifolds but so far on the road 4 years no icing issues.
I do have a trick for the factory hot air asst. choke on the carter carb when running EFI manifolds and can be used for headers also.
Dave ----
BTW you will want to run the EGR plate as a spacer or the throttle cable will not pull right.
My valve is blocked off like you did on the intake with the plug and no vacuum to valve.
Some have cut the valve off and filled the end with JB Weld to finish it off as they did not like the valve hanging off the side of the like it dose.
I wanted the under hood of my 81 F100 to look close to factory stock.
Dave ----
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