FE-FC Holden Discussion Forum

I know i must sound really green, but the only stupid question you can ask, is the one you don;t ask.....so can anyone please help explain the Vacuum on a RED 202.

In other words, there is a vacuum outlet on the INLET MANIFOLD, and there are 2 vacuum holes on the top of the chrome rocker cover, and I know brakes will need a vacuum hose connected to them......but can anyone explain, what goes where, and in what order the vacuum comes from and goes to.....

That's the beauty of buying an engine in parts, and putting the jigsaw together.

Thanks again folks

Mark

Mark,

The fitting on the inlet manifold is where around 12-14"Hg Vacuum is present at engine idle. The vacuum is created by the cylinders drawing the fuel/air mixture into the engine - the induction stroke in a 4 stroke engine.

The vacuum is used for various purposes

* to scavenge unburnt fuel and oil fumes from the  crankcase (this is the fitting on top of the rocker cover)

*vacuum for the power brake booster

*vacuum advance on the distributor (to advance the timing as more vacuum is drawn into the engine - when you put your foot down)

* some heater controls on later models

* various emissions switches, especially on the later Commodore sixes.

In a 4 stroke engine there are four parts to the engine process:

1. Induction - air/fuel is drawn into the engine by the downward movement of the piston via the carburettor/inlet manifold/inlet valve

2. Compression - the fuel/air mixture is compressed inside the cylinder by the pistons upward motion

3. Firing (or Power) - the spark plug ignites the compressed mixture causing the piston to travel back down. Spark plug is normally fired just Before the piston reaches its uppermost point, or Top Dead Centre. This is why you see timing given as 6.0 BTDC

4. Exhaust - the waste gases produced as a result of the firing stroke are evacuated by the pistons next upward movement/exhaust vavle/exhaust system.

Hope this helps your understanding of what's happening.

cheers,

Craig.

Hi Mark,

the accomp pic shows how I've got mine set up....

I use the tapping on the rear of the manifold for the power booster vacuum hose...

I connected the rear rocker cover opening using a PCV valve to the tapping on the manifold just below where the throttle body meets the manifold

I connected the front rocker cover opening to the air filter venting point, just inside of the filter element

I connected the distributor advance to the tapping on the RH side of the carburettor body...

Of all the connenctions, the one I'm least sure about is the last one....I heard from one mechanic that it depends on the distributor/points cam as to whether the vacuum opening should be above or below the throttle plate.....apparently different red motors had the tappings at different points on the carby to suit different distributors/cams......can anyone else add to this?

regards......Brad

Craig,

You forgot the most important use for vacuum on an FC........... clear, unrestricted vision in the harshest of rain storms on a steep incline! (The wipers!)

Regards

Ed

Yea Edward,
       You don't have those " silly metal stick things" going backwards & forwards on the windscreen , in front of your eyes  ;D

         Norm    :)

Thanks Brad & Craig....you info has helped me quite a bit.

Sorry for the delay in thanking you for your replies....been a bit busy !

Cheers

Mark