Hot slot intake manifold

[dmjlambert]

Here's my 1969 CST/10 with 350 engine. I learned to pay attention to the hot slot intake manifold, it has a smile on it. These are mentioned every great once in a while on the forum as I see from my recent search. I didn't know what the thing was called until this week.

I found some really good information here from Lars Grimsrud:
https://www.corvetteforum.com/forums...d-problem.html

The exhaust ports on my hot slot are blocked off by my engine rebuilder guy. The slot is still there to spoil ideas about justing just any old Quadrajet gasket, as seen in my pictures. My engine was whistling. So, I installed the carburetor using the factory-style gasket set. If I was really determined to convert without buying a different intake manifold, I would do a redneck fix and fill the slot with JB Weld and sand it flat. But it hasn't come to that yet. Posting pictures for your entertainment.

[kwmech]

The JB weld may hold, but I have my doubts. In the past I just made sure hole was drilled to 7/16'', and threaded an allen head 1/4'' pipe plug in on both sides to plug off the blow holes. Then filled in with JB to flatten out the area where it seals. OR you can buy an aluminum intake

[Steeveedee]

I disagree with Lars from your link. There is very little pressure from exhaust gases in the first place, and once the heat riser opens, there is even less. This design is a compromise reached by engineers working on making the vehicle work in any environment, within reason. Depending on what your guy did to close off the ports, you may well be done with trying to stop the heat flow (it goes up hill, so that area is still getting hot). If you want to keep the manifold, ask your guy what he did. It may not require any more work.

[dmjlambert]

Originally Posted by Steeveedee

I disagree with Lars from your link. There is very little pressure from exhaust gases in the first place, and once the heat riser opens, there is even less. This design is a compromise reached by engineers working on making the vehicle work in any environment, within reason. Depending on what your guy did to close off the ports, you may well be done with trying to stop the heat flow (it goes up hill, so that area is still getting hot). If you want to keep the manifold, ask your guy what he did. It may not require any more work.

I don't think I need any more work, but I do need to be mindful to not try using gaskets that are not designed for this manifold, and that means I don't need to be using that 1/4" thick gasket that came with my remanufactured carburetor. If the exhaust holes had not been blocked on my intake, I would have been sucking a lot of exhaust into the engine while using that incorrect gasket. Since my holes are blocked, I could get away with just using the proper shaped composite gasket and no heat shield, but I went ahead and put both gasket and heat shield on there anyway.

When you say you disagree with Lars, what part is there to disagree with? I think his article is just explaining how it works and what gaskets to use, because people often use the wrong gasket (like I did).

[dmjlambert]

Just adding a note, so this thread serves as documentation. I didn't mention the vacuum leak earlier, that is the reason for figuring out the gaskets. The whistling was caused by a vacuum leak through the hot slot caused by using the incorrect gasket on a hot slot manifold with blocked exhaust holes.

[StingRay]

Damn that brings back memories. I put one on my Chevelle in High school. I was missing that thin steel shim that covers the slot. I got a big surprise when I went to start it.

[68Gold/white]

I've used 1/4" pipe plugs, cut off the ends of 3/8" bolts and bought 3/8" set screws

You really need to plug those holes. It's old technology. Trying to heat up the carb base for better fuel atomization, especially in cold weather. The exhaust gases erode the base gasket (even the correct one), and make a vacuum leak. If you thick base gasket didn't have that gap forward of the 2 primary holes, it might work...