78 440 dual plane intake threaded hole

[jeepthrills01]

I was removing my leaky TQ for a swap meet acquired 4150 which I just went through for my 78 motorhome 440....and I noticed a large threaded hole in the floor of the manifold on the passenger side under the primaries. And a hole about half the diameter on the driver's side with a smooth bore. I'm assuming this is for flow equalization...but every pic I've seen of a factory cast intake seems to have a "metering oriface" in both holes. All my previous motors have already had an aftermarket....and it was over 20 years ago...so may have just not noticed if any of them had it before. Every Google term I come up with isn't even close.....someone with deeper knowledge care to reveal it's secret?

 

[BeepBeepRR]

From another site. The picture they showed was a small block 2 bbl intake. My 75 RV engine had it too. I was swapping intakes anyhow.

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

 

[jeepthrills01]

So having one fully venting into my intake charge....that would explain a few idle anomalies . Thanks for the quick response.