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Does anyone know what these "things" are or do? On a 73 dart custom
- Thread starter Matt B
- Start date
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Those are 73 only pieces. The left one goes to the distributor vacuum advance. Not sure about the other one. Early attempts at emission control.
@slantsixdan can tell you exactly what they are called and what they do.
gunbunny
Well-Known Member
Pretty sure those are EGR & Distributor ported vacuum switches.
Those are a doo hickey and a thing-a-mabob...
69_340_GTS
Well-Known Member
CARB = California Air Resources Board
TrailBeast
AKA Mopars4us on Youtube
That one on the left makes a nice access to clean your cowl out.
Yea, early smog stuff and not needed.
Google the part #'s. I'm Google smart!
slantsixdan
=..=
The dingus on the left (outboard) is an OSAC valve, "Orifice Spark Advance Control". Its job is to delay vacuum to the distributor for 7 to 17 seconds so the '73 cars could squeak past their Federal emissions type-approval tests and be legal for first sale. Notorious for causing hesitation, mushy acceleration, and poor driveability. You're best off leaving it disconnected; run the vacuum advance hose directly from the correct port on the carburetor to the distributor. The "CARB" stamp does not refer to the California Air Resources Board, it indicates which port originally got the hose from the carburetor.
The inboard dingus is a thermal vacuum switch. Its job was to block vacuum to the EGR valve below a certain ambient temperature. According to Chrysler, this was installed because at very low temperatures there was less tendency for high combustion chamber temperatures to form NOx, so under those conditions there was no need to suffer the driveability hit caused by EGR. According to EPA, that's a load of poo and this was really installed because the Federal emissions type-approval test protocol didn't include operation at the low temperatures when this dingus deactivated the EGR.
It was one of the first times EPA accused an automaker of installing an emissions control defeat device. Was it a bogus accusation? Maybe or not; that can only legitimately be answered by looking at emissions data with and without that dingus. It's academic at this point; if I were in your shoes I would permanently disable the EGR (remove valve and install blockoff plate with a new gasket is the neatest/cleanest way...or remove valve, flip it 180° and reinstall it with a new gasket…or leave the valve in place rightside up and just make sure no vacuum reaches it).
Since we are talking about making a Slant-6 Dart run better: find tune-up parts and technique suggestions in this post. Do the Fuel line mod and the HEI upgrade . Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. And see this thread.
The inboard dingus is a thermal vacuum switch. Its job was to block vacuum to the EGR valve below a certain ambient temperature. According to Chrysler, this was installed because at very low temperatures there was less tendency for high combustion chamber temperatures to form NOx, so under those conditions there was no need to suffer the driveability hit caused by EGR. According to EPA, that's a load of poo and this was really installed because the Federal emissions type-approval test protocol didn't include operation at the low temperatures when this dingus deactivated the EGR.
It was one of the first times EPA accused an automaker of installing an emissions control defeat device. Was it a bogus accusation? Maybe or not; that can only legitimately be answered by looking at emissions data with and without that dingus. It's academic at this point; if I were in your shoes I would permanently disable the EGR (remove valve and install blockoff plate with a new gasket is the neatest/cleanest way...or remove valve, flip it 180° and reinstall it with a new gasket…or leave the valve in place rightside up and just make sure no vacuum reaches it).
Since we are talking about making a Slant-6 Dart run better: find tune-up parts and technique suggestions in this post. Do the Fuel line mod and the HEI upgrade . Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. And see this thread.
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Dusterdenovo
Contentedly Old School
FYI, DMT sells those gaskets for a buck a piece. Top quality.
Mr. Sinister
Devastation Manager
Nothing....only used on the Left coast.
Remove and discard you will never use them.
Unless you intend to restore to OEM.
Remove and discard you will never use them.
Unless you intend to restore to OEM.
slantsixdan
=..=
No, the OSAC valve was present and hooked up as original equipment on all '73s and many '74-'75-'76 cars, no matter what state they were sold in. They were even present on Canada-spec cars, though Canada's emissions regs were not as strict as the American regs until '88-'89. The thermal vacuum switch was on most early-production and a fair percentage of late-production '73s, again regardless of where they were first sold.
I've had a couple of '73 models and I just weld in a patch over those, prime, fill, sand and paint. Afterwards, it is as if they were never there.
Yep all 73's A,B and E had them in the cowl plenum.
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