Holes in manifold

[old guys rule]

Two holes at the bottom of the plenum beneath the primaries. Purpose?

 

[BeepBeepRR]

What year intake? Pretty sure they were in there on later style intakes for emissions purposes. I may be wrong, my 75 440 intake had them. Or Early style EGR for making them emissions compliant. Did some googling and yup early EGR emissions crap.

Holes drilled in the intake?

Howdy people, I have a pretty straight forward question. I aquired this Edelbrock Performer 318/360 dual plane intake in a parts deal. Upon initial inspection I noticed that there is a hole drilled in the bottom of each plenum, and am wondering…. Why? What for? How come? WTF? Is it junk? Is it...

www.forabodiesonly.com

 

[Lefty71]

I think they were called "floor jets" for EGR. I'd tap and plug them.

 

[Fran Blacker]

Hiding Nitrous .

 

[RJRENTON]

Two holes at the bottom of the plenum beneath the primaries. Purpose?

The first year (1972) 340 engines with cast iron manifolds used FIXED EGR metering orifices connecting the intake plenum with the exhaust xover passage, metering a fixed ammount of EGR ALL THE TIME. In 1973 Mopar and aftermarket manifolds (Edelbrock or "Eddy") used an external EGR regulating valve, the best SOLUTION as suggested is to drill/tap the plenum holes using flush mounted NPT pipe plugs as well as the external EGR metering passageways. Others may have alternate suggestions....
BOB RENTON

 

[old guys rule]

The first year (1972) 340 engines with cast iron manifolds used FIXED EGR metering orifices connecting the intake plenum with the exhaust xover passage, metering a fixed ammount of EGR ALL THE TIME. In 1973 Mopar and aftermarket manifolds (Edelbrock or "Eddy") used an external EGR regulating valve, the best SOLUTION as suggested is to drill/tap the plenum holes using flush mounted NPT pipe plugs as well as the external EGR metering passageways. Others may have alternate suggestions....
BOB RENTON

I have heard that there is an advantage to using EGR. Can't remember what it was possibly cooling mixture and suppressing detonation. Sound right?

 

[old guys rule]

Hiding Nitrous .

Liking that idea!

 

[RJRENTON]

I have heard that there is an advantage to using EGR. Can't remember what it was possibly cooling mixture and suppressing detonation. Sound right?

EGR was introduced in 1973 nation wide (1972 California) as a way to reduce the Oxides of Nitrogen, or Nox (Nitrogen Dioxide NO2 and Nitric oxide NO) emissions by LOWERING combustion chamber temperature to less than 1500°F by introducing exhaust gas to the incoming fuel charge. What it did was to reduce performance, introducing stumbling/poor low speed performance and reduced fuel mileage. Ignition advance characteristics changed to try to compensate. Reducing detonation....yes....but also performance....
BOB RENTON

 

[multimopes]

Hiding Nitrous .

Believe it or not. I had 1 or 2 of them under my intake. They were threaded. I plugged them. My car was a former race only car. I do believe it was for nitrous, lol!

 

[old guys rule]

EGR was introduced in 1973 nation wide (1972 California) as a way to reduce the Oxides of Nitrogen, or Nox (Nitrogen Dioxide NO2 and Nitric oxide NO) emissions by LOWERING combustion chamber temperature to less than 1500°F by introducing exhaust gas to the incoming fuel charge. What it did was to reduce performance, introducing stumbling/poor low speed performance and reduced fuel mileage. Ignition advance characteristics changed to try to compensate. Reducing detonation....yes....but also performance....
BOB RENTON

Makes sense to me. I'll have to tap them to plug them. I always plug off the EGR holes. All manifolds aftermarket that I've had they were already plugged in the plenum. Thanks for the heads up, Dave

 

[Mackman]

I may be mistaken, but I seem to recall those holes were originally tapped and a threaded “floor jet” was screwed into them. Over time they burned out and became bigger. I had seen them welded shut.