dodgem880

What is is the purpose of the two items pictured down in the opening of the my intake manifold? If I had to guess I'd say they have something to do with the heat riser system but, I'm not sure.

LA-360

I've also noticed these on my LA-318.

Thanks

Coronet 500

They are orifices to inject a small amount of exhaust into the intake charge and help reduce emissions. Most people will plug them.

dodgem880

Alright Thanks

Do they unscrew or are they pressed in?

Gorts 5th

Get a new manifold or plug em...

dodgem880

Thanks but, I don't intend to do either. I'm just wondered what their purpose is and wanted to learn more about them. They must be an obscure subject, I can't seem to find the keywords to research this on my own. Is there a technical term?

Would it be a stupid question to ask why one would plug them?

In the picture:

the one on the left has a hex base so I would guess you can unscrew it and thread a plug in the hole? Something like below?

Why does the right side look different? Is it already plugged?



Why does the right side look different? Is it already plugged?

Coronet 500

Plug them to gain some performance. Can't remember if they are straight thread or tapered pipe thread.

Picture is hard to make out with glare. Can you pass any thing through it?

dodgem880

Thanks for the reply.

To be honest I didn't try. I took this picture before I put my carb back on and since this engine is in a truck I didn't climb up to look at it myself, just used my phone. I could see the stud from were I was but, didn't know about the left port until after I took the picture. Next time I have the carb off either of my trucks I'll see if I can poke it. You would think that would cause a serious problem if it was an open hole with no metering orifice. IF it is plugged maybe it's because that is the same side of the manifold the EGR valve would go. (If I had one)

Anyway, so I couldn't find anyone talking about this using "mopar OR dodge OR chrysler" in my google searches.

But, I though to myself "so... it's like EGR without the valve?"

Wikipedia search EGR
Bingo.

I see why people plugged them but, I haven't noticed any problems so I'm fine with them (for now).

I had trouble finding it because 1) did know what it was 2) assumed it was something exclusive to Chrysler products.

dodgem880

Update.

I did a reseal job on my intake manifold. While I had it off I decided to investigate these egr orifices. As I suspected the side with the hex base unscrews. The other side is just a bored hole. The two are connected together underneath the intake runners.

I blew compressed air in one side and it came out the other. Same when I filled one side up with solvent. Nothing came out of the crossover runner (yes I knocked the carbon out of them). So, it seem they don't function or go anywhere. I suspect it's because my EGR valve is plated off. I went ahead put the jet back in. It appears to use pipe thread as it screwed easily into a 3/4" pipe fitting.

I believe fuel pools down in them. Thats whats causing the glare in the original picture I took.

So, these aren't like the first egr systems mentioned in the above Wikipedia quote it seems.

Other than obstruction to flow, do they do anything else?

Could I have just left the jet out without plugging the hole?

Coronet 500

Definitely Plug them.

RacerHog

Yep.... What He said....

dodgem880

Well, like I said I put the "jet" back in. I could go back and plug the threaded sided but, it's probably too late for the bored hole side. I've already reinstalled the intake. I don't want to risk getting metal cuttings into the engine by tapping it now. Would plugging the one side be good enough? that would do at least two things I believe:

• Get rid of that big metering jet
• Block the connection between the two sides (What effect that has I do not know.)

However, I'm still trying to understand the purpose of plugging these. Is this more about eliminating restriction to flow or stopping the exhaust gas from recirculating? Because in the latter case didn't I prove these orifices do not function on my intake?

I'm just trying to better understand the advantage of doing this based on the "experiment" I did.

Coronet 500

The liquid you poured in went into the exhaust manifold or into the cylinder if the exhaust valve happened to be open.

dodgem880

I did that with the intake manifold off of the engine. So, the cylinders and exhaust manifold were out of the picture.

Coronet 500

dodgem880

Thank You for the diagram.

That's exactly how I expected my intake to be but, I do not believe that is the case.

However, Your diagram gave me inspiration to try and find a Chrysler version



My intake seems to resemble the diagram on the right. It has provisions for an egr valve but, it is plated with a blank and metal gasket. It even shows only have one "floor jet" like mine.

However I do think my crossover runs all the way through because when I had it in the solvent tank cleaning it up. I stood it up vertical long ways and ran solvent down the crossover port and solvent came out the other side.

There does seem to be some kind of partial obstruction at the entrance of the egr valve side port. Its hard to explain. but fluid can go around the sides of it. I think it 's like a chamber or baffle for the egr valve.

edit:

something I just thought of. The EGR provision is on the driver side. The heat riser valve is on the passenger side. The flow would be from left to right not right to left like in the diagram. I also wonder if the EGR system, that is the passage for the floor jets is somehow segregated from the heat riser system that's used to heat the carburetor and run the automatic choke? This is confusing, I'm probably putting too much thought into it. At the end of the day it doesn't really matter I suppose.

dodgem880

I found the following on a ford forums but, I can't imagine why the emission technology would be any different.

https://www.ford-trucks.com/forums/8...ml#post7217740
Plus, based on what I saw with my manifold, this makes sense to me. That's why I couldn't get air/fluid to pass from the meters holes to the cross over ports because they don't lead directly to the exhaust crossover.

Because, if they did. What purpose would the EGR valve serve? It wouldn't be able to stop flow to the meter orifices, it would technically be bypassed.

The meter holes are on a separate runner that is "fed" from the EGR valve provision which in my case is permanently closed because it's plated off.

Am I making any sense here?