I still don't understand the concept of vacuum completly.

Where does it come from?

Why is a leak bad?

What does it do for the engine?

Please enlighten me, I need a clue.

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1985 Camaro IROC-Z LB9

1989 Pontiac Firebird
Formula W6S LO3 TBI 305
-180 degree stat
-Hooker Cat-Back

 

Well...

Vaccum Sucks.
No Really, it Does

Vaccum Is a Lower than Atmopheric Pressure, Or area of it. Inside Your Intake manifold, and Carb, and Cylinders partially, Is Vaccum. That is to Say a lower than the surrounding atmospheric Pressure. This is Caused Essentially By The Pistons Pulling Back, creating Open Space W/o Any air in them, TO Put it Simply. This Causes Air to be sucked in Via the Intake Valve ( Funny how that works... ) Wich In Turn pulls Air Out Of the Intake manifold, Wich Pulls In Down through the carb, Or throttle Body On a FI car. So whats a Vaccum Leak Do ? it allows Air to get Into the Mix Via a Path that isnt through the Carb. Whats this Do? Lots of things, None Of wich help your Car Run very well

Sorry If that was a ***** Explination, but its late



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Livin' the Stereotype

 

following up that question...


How does the car control the vacuum? (i.e., how does it know when to open the thermac, the yatta yatta)

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89 iroc-z 305 tbi
everything stock, except for a mirror that fell off

 

Oh ok, that's about what I thought. Ok here is another one.

How do different cams change the amount of vacuum? I know it probably has something to do with the opening position of the intake valve.

 

Pop!, goes my brain.

If there is a vacuum leak then the raises the pressure inside the manifold and therefore the outside air doesn't push through the fuel as fast, plus the air that comes through the leak doesn't get any fuel mixed with it.

Am I on the right track there?

 

Keith,

Final answer?

You're right! The vacuum is actually created by the engine pumping air from the intake side to the exhaust side. It is a fairly efficient air pump. When it pumps more air out than is allowed to enter, the intake side enters a state of low relative pressure, or partial vacuum. The inward flow of air caused by this pressure differential is what is used to carry fuel into the combustion chambers. A leak in the system can cause a different amount of fuel to be carried to different chambers, resulting in rough, uneven operation.

The amount of vacuum is regulated by the speed of the engine (air pump) and how much air is allowed to enter the intake (throttle position). Opening the throttle will increase pressure in the intake (lower vacuum) until the engine speed increases. As the engine speed increases, it pumps more air out and again establishes a level of vacuum in the intake side. For this reason, it is important to increase the amount of fuel available to the engine at larger throttle openings. The more dense fuel charge creates more power and causes the engine speed to increase to a point where the pressure differential is re-established at a desirable level. Conversely, and engine that is running at higher RPM and has a closed throttle will create a larger pressure differential (vacuum). In this situation the engine should get a lower density of fuel charge so that the engine speed can reduce.

BTW - It sounds like you've grasped the theory, anyway. Just remember that the engine is basically an air pump. More air flowing allows more power to be generated. It's as simple as that. Anything you do to modify your system for more power production should fit that theory. As long as you can keep your fuel system at a point where it can administer the appropriate amount of fuel to mix with the incoming air, the sky's the limit for power production. Some of us lose sight of that at times...

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Later,
Vader
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"No matter how hard you try you can't stop us now"
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