That sounds like a little better answer. It's amazing all the crap they will put on a car. I bypassed all that, the first thing I did was flip the air cleaner lid, and remover the plastic scoop inserts in the hood. Probably didn't help much, but at that time in life I thought it did. JTS 71 Mach1
I have never been convinced flipping the air-cleaner lid did anything to help the engine run...simply because if it did, the OEM designers would have just designed it to gulp more air. But who knows?
Taking the air scoop block-off plates will not do anything other than allow water and dirt all over your engine!
But...removing them sure does alleviate the obvious "fakeness" of the scoops visible to anyone who looks at them!
The plastic thing inside the air cleaner against the outer sidewall is a holder for the foam breather element (#FB-59), part of the PCV system.
The PCV valve (located in the top of the oil-fill cap on the drivers side valve cover) pulls oily air vapors from the top of the crankcase, and routed them back into the carb (through the vacuum hose in the back of the carb) and engine so as to be 'reburned' for cleaner emissions.
But, since inducing a vacuum into the crankcase via the PCV system could cause a host of issues( Oil consumption, loss of power, valve cover leaks, etc...), a "breather" system is incorporated.
This is the "path" of air into and out of the PCV system:
1) fresh air enters the air cleaner
2) fresh air is drawn into and through the foam breather element (the #FB-59 unit) and down through the hose leading into the passenger side valve cover.
3) This fresh air mixes in the crankcase with the oily vapors from combustion that are in the crankcase, diluting it somewhat.
4) vacuum from the PCV valve located in the driver side valve cover (on the other side of the engine) draws this oily vapor OUT of the crankcase and routes it into the rear, base of the carb.
5) This oily vapor is mixed with the incoming fresh air charge going into the carb, to be reburned during combustion.
If you do not have a functioning breather system hooked up, your PCV valve cannot work properly leading to sludge build up and dirty oil after relatively few miles. This is the earliest of "emissions control devices" and is one of the good ones! You need it!
The PCV system has an important function when the engine is NOT running also:
When the engine is shut off, all vacuum bleeds off (naturally) and a spring-loaded plunger within the PCV valve closes, blocking any oily vapors from floating up through the PCV valve, through the hoses to the carb, and up and out, into the surrounding air.
The vapors could still float out the other "end" of the system, the breather (#FB-59) on the other side of the engine, so a foam element is placed in there to catch and trap the heavier-than-air oily vapors as they pass through the foam, and into the air cleaner interior.
The entire air-cleaner assembly however is a sealed unit, trapping any dirty/ oily air vapors within the air- cleaner, gulped down into the carb at the next start-up.
This is the reason no "open element" air cleaners could be used on OEM cars past 1968 (1965 in California, I think). A "sealed crankcase" is required on all OEM vehicles since then.
When Ford was defending themselves from the tree-huggers attacking them about their evil and gigantic Excursion, Ford made the public comment that...
"...driving down the highway at 55MPH for ONE HOUR in a new Excursion produces fewer emissions than a properly-functioning '65 Mustang 289 does sitting in a parking lot with the ENGINE TURNED OFF for the same hour."
This is mostly due to the effectiveness of the PCV system (not yet mandated on a '65 Mustang) which traps vapors in the system while the engine is turned off.
Got these pictures from the 1973 Mustang Part & Body Illustrations. Wanted to post them here in case anyone else in the future is trying to piece this together. You still have to do some leg work and look up part numbers if you aren't sure what you're looking at.
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