318 heads, 302 casting. Mystery holes?? (Solved!)

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Righty Tighty

Blame it on the dog
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I’ve got the engine on the stand and pulled off the exhaust gaskets, and found a hole under each exhaust port that hadn’t been plugged. The holes are threaded and go directly into the port, and since they weren’t plugged, were leaking exhaust.
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What are these holes for? My guess is that they’re for stock manifolds, and since the flanges on my headers don’t have holes for them, they were overlooked.

Next, what should I do? Should I simply plug them with a screw of the same pitch and call it good?
 
They are air injection ports. (pollution control) As long as they are threaded, plug them up.
 
I always tap them to 1/4-20 and screw set screws into them sealed with high temp rtv.
 
Thanks guys. Turns out they’re the same pitch and diameter as the valve cover studs. Rusty, is there any particular reason you tap them to 1/4-20?
 
Thanks guys. Turns out they’re the same pitch and diameter as the valve cover studs. Rusty, is there any particular reason you tap them to 1/4-20?

If they are the same as the valve cover fasteners, someone has already tapped them to 1/4-20. And yes there's a reason I tap them. Because they are not tapped from the factory.
 
Well let me apologize for the stupid question, because I just now realized that those studs are indeed 1/4-20. I’m a big dummy. BUT, thankfully they’re already tapped, because all I need to do is pay a visit to the hardware store and pick up some set screws.

Here’s a question that’s unrelated to the holes, but related to the heads. I noticed most of the valves are pretty sooty looking. Does that mean I’m running rich?
 
Well let me apologize for the stupid question, because I just now realized that those studs are indeed 1/4-20. I’m a big dummy. BUT, thankfully they’re already tapped, because all I need to do is pay a visit to the hardware store and pick up some set screws.

Here’s a question that’s unrelated to the holes, but related to the heads. I noticed most of the valves are pretty sooty looking. Does that mean I’m running rich?

I didn't see a stupid question. You don't know unless you ask.

Could be running rich. Could also just be exhaust soot. Get it back together and running and you can fine tune it from there.
 
With a set of headers they'll also leak badly, and make a really bad exhaust leak sound.
 
With a set of headers they'll also leak badly, and make a really bad exhaust leak sound.

That's just flat out untrue. With GOOD, STRAIGHT header flanges, GOOD header gaskets like Remflex and a GOOD set of header bolts, they will not leak.That may have been your experience with inferior parts, but not everyone has the same experience by FAR.
 
With a set of headers they'll also leak badly, and make a really bad exhaust leak sound.
I did have a few leaks with the Fel Pro gaskets, went to Remflex and it solved the problem. (Except for the injection ports I missed)
 
I did have a few leaks with the Fel Pro gaskets, went to Remflex and it solved the problem. (Except for the injection ports I missed)

Also make sure the flanges are straight AND all the welds on the tubes at the flanges are straight, level and on the same plane. Esay enough done by placing the headers on a smooth flat surface like the concrete floor and getting a mirror and looking for daylight under the welds. If you see some, just file the welds down appropriately. A lot of people think you can just sling a set of headers on, but they are like any other aftermarket part and often require mods to make work correctly. Once everything is straight and flat, you'll be hard pressed to MAKE a set of headers leak. Even a cheap set.
 
That's just flat out untrue. With GOOD, STRAIGHT header flanges, GOOD header gaskets like Remflex and a GOOD set of header bolts, they will not leak.That may have been your experience with inferior parts, but not everyone has the same experience by FAR.
Talking about header flanges, I cut the bars between the ports. I have had very few leaks doing this. The header companies weld the tubes to the flanges and grind the welds (not surface them so they are all parallel and flat) By cutting the flange, it isolates the ports from the others in case there is any warpage. Even cheap thin flanges can seal
 
Talking about header flanges, I cut the bars between the ports. I have had very few leaks doing this. The header companies weld the tubes to the flanges and grind the welds (not surface them so they are all parallel and flat) By cutting the flange, it isolates the ports from the others in case there is any warpage. Even cheap thin flanges can seal
I have TTI headers, and like you describe the flanges are one piece all across. It seemed peculiar to me, but I didn’t want to go cutting into some really expensive part without knowing whether it would help or hurt.
 
That's just flat out untrue. With GOOD, STRAIGHT header flanges, GOOD header gaskets like Remflex and a GOOD set of header bolts, they will not leak.That may have been your experience with inferior parts, but not everyone has the same experience by FAR.
Let me clarify my remark. My son's first truck was an '83 W150. He showed up one day with a new set of headers that sounded terrible. Inspection showed he didn't plug the AIR holes. I fixed the problem by installing a set of earlier heads that didn't have AIR holes. Problem solved.
 
Let me clarify my remark. My son's first truck was an '83 W150. He showed up one day with a new set of headers that sounded terrible. Inspection showed he didn't plug the AIR holes. I fixed the problem by installing a set of earlier heads that didn't have AIR holes. Problem solved.

That's certainly one way to do it!
 
I have TTI headers, and like you describe the flanges are one piece all across. It seemed peculiar to me, but I didn’t want to go cutting into some really expensive part without knowing whether it would help or hurt.
I stated what I did as a side bar of information. I have a pair of 302's and I bet some headers with a small flange (not talking thick) will not cover the 302's AIR ports unless they are plugged. Those holes are just too far away from the exhaust port. Easy to see in the photos on post #1. By cutting the flange between the first, center, and rear tubes, it isolates them making them un effected by the whole flange.
 
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I learned my hard way lesson on the air holes with an 84 D350, when I put headers on it. Fired it up, and PHTT, PHTT,PHTT....lol. Fortunately, there is 4 miles of room in a truck..so I was able to move the headers, tap the holes 1/4-20, and plug em up with allen head set screws.
 
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