On the bottom of the offenhauser intake manifold there is an opening. I orginally thought/believed it hooked into the exhaust manifold. Kinda like a re-circulating of the exhaust gases.

I just got my headers for the truck in the other day. They are from hedman and have no place to attach to the intake manifold, so I guess my orginal idea is out. I have done the searches here in the Tech Articles, and in the forum, along with over at Ford Six. I also posted up a similiar question over there.

I need a new intake manifold anyway, because I sold the previous one(long story.) Do I need to look for one that does not have that opening on the bottom?

Any help or insight is appreciated.

 

No, your original idea is correct. People that do headers or the EFI exhaust manifold swaps no longer have the heat riser attached. The void in the stock manifold, as well as in the offy units can just be left open. Obviously, in the stock configuration, it has exhaust gases in there. It does not communicate with the intake in any way.

Now, this is an issue that you perhaps should have read up on beforehand. Some searches for "heated carb" "heat riser" "warm air aircleaner" "heated carb plate" "intake block off plate" might net you some interesting reading. Once you have put headers on, your carb and intake no longer have a source of heat. If you live in warmer climes, you are ok. And actually, you are OK if its cold and DRY, too, though your fuel economy may suffer some during very cold weather. But if you live in areas prone to damp weather around the freezing mark, then you will get carb icing. Ever notice how gas evaporating from your hands makes them cold? Well, atomization of gas in your carb does the same thing -- in certain situations your carb will start to look like a froze up airconditioner coil. The carb will drop to a temp around zero and the damp air will start to just condense out and turn the carb into a block of ice on the outside. Eventually things can just stop working.

I personally intend to heat the base of the offy (or in my case edelbrock) intake by makeing a block off plate that bolts to the bottom of the intake. Once the void in the base is sealed, I will plumb and run water (via heater hoses) through the base. This should work -- have seen pictures somewhere, but I didn't copy them so cannot show you.

Good luck.....