ported vacuum switch

[dan1s]

On a ported vacuum switch for a 68' 442 does anyone know the setup (where each port goes)

I have the top port going to the distributor. The middle port going to the carburetor. And the bottom port going to the intake manifold.

Is this correct?

Thanks, Dan

[Oldsguy]

do you mean the one pictured in this thread? http://classicoldsmobile.com/forums/...valve-vrv.html
or this thread? http://classicoldsmobile.com/forums/...2832-dtvs.html

[dan1s]

Dan,

No to both of these threads. This switch is located at the front of the motor in the intake manafold. My car is a 1968 442 with a 400cid

Here is a picture of a new one.

[texasred]

If it is like the 69 (and I'm not saying for sure that it is) then the top port goes to the advance on the distributor; middle port to ported vacuum on your carburetor; bottom port to manifold vacuum forward and left of the carburetor.

C.J.

[dan1s]

C.J.

Thanks, welll it looks like mine is bad. I can't get any Vac. to the top port.

Why is it pulling vac. from the carb. and the manifold?

Dan

[texasred]

It won't open to allow ported vacuum advance until the engine is warm, which is why it is in a water port, and it has manifold vacuum Try it again with the engine warm or you can just bypass it altogether.

C.J.

[dan1s]

C.J.

Thanks,

What is the purpose of it ported to the carb?

Dan

[texasred]

Not sure, Dan. I got that bit of info from a post I copied a while back. I keep some strange info sometimes.....wish I knew/could tell you more.

C.J.

[dan1s]

C.J.

I just got this info from another forum that I belong to.

"During normal engine operation, the vacuum advance canister receives vacuum from the carburetor body, which means there is no vacuum advance at idle. When the engine is overheated (about 240°F), the switch connects the vacuum advance canister directly to manifold vacuum, which is supposed to raise idle speed, which is supposed to make the engine run cooler. Unless you need this part to have a "correct" restoration or have a very large camshaft, bypass it and connect the vacuum advance directly to the manifold."

So all my questions have been solved. Thanks

Dan

[joe_padavano]

Originally Posted by dan1s

C.J.
So all my questions have been solved. Thanks

Dan

Well, not quite...

Just for completeness, disabling of the vac advance at idle and small throttle openings was done in the late 1960s as an early way to comply with federal NOX emissions requirements. Unfortunately, this method also resulted in engine overheating, which is why the thermal vac switch was used to restore the advance at high engine temps. All this hardware became moot once EGR valves were mandated in 1973.

[88 coupe]

Originally Posted by joe_padavano

........ disabling of the vac advance at idle and small throttle openings was done in the late 1960s as an early way to comply with federal NOX emissions requirements ........

Your use of the word disabling, implies that Olds did not use ported vac advance prior to that time, which would not be accurate.

........ Unfortunately, this method also resulted in engine overheating ........

Nothing to do with ported advance. Everything to do with using less initial advance, at idle.

........ which is why the thermal vac switch was used to restore the advance at high engine temps ........

Make that, at high idle temps, as that was when the overheating might occur.

Norm

[88 coupe]

Got sidetracked and forgot about the original topic.

Originally Posted by dan1s

........ which means there is no vacuum advance at idle ........

Which is the way it has always been done.

........ Unless you need this part to have a "correct" restoration ........

Doesn't matter matter whether it is bypassed or not.

The switch has no effect on the normal operation of the vacuum advance. It is only used if the car overheats at idle, due to inadequate initial advance.

........ or have a very large camshaft ........

If the cam is that large, the choice of vacuum source would be a non issue.

........ bypass it and connect the vacuum advance directly to the manifold ........

The factory used "ported" vacuum for a reason (actually two).

I suggest you compare both, to find out whether your "internet source" is more reliable than your Factory Service Manual.

Norm

[Sam Barrett]

If you go to Fusick and order the Maintenance manual for that year, it show specific set up instructions for the Distributor Vacuum Control Switch.

It varies for different years for example a '71 and '72 have a four port switch that uses the atmosphere, the manifold, the carb ported vacuum as well as thermal control and transmission control of the source for vacuum.

[liftrocket]

I have a 72 Cutlass with a 350-4bbl. During a rebuild, the Distributor Vacuum Control Switch (four ports plus electrical connector) went missing. I have been trying to find one and have learned that it is nearly impossible to find a new one. Parts stores and catalogs point to the three port without electrical version. I have been looking for a diagram as to how to hook this up on my 72. My service manual shows how to hook up the original type nicely but not this simpler type.

On this new part (STANDARD MOTOR PRODUCTS Part # PVS1 {PORTED VACUUM SWITCH}), the ports are labelled from top to bottom "1", "D", and "2" and no documentation came with it. The mechanic I talked to thinks the bottom port goes to the manifold, the middle "D" port goes to the distributor, and the top port goes to a port on the carb (not sure which).

A pic of the new part can be found at http://thegraves.ca/72Cutlass/new.jpg

I would appreciate tips on how to hook up the hoses for this.

Thanks!

[J-(Chicago)]

does this help? http://www.classicoldsmobile.com/for...ol-switch.html

You can use the search link on this site to see if someone else has been through the problem once already.

[liftrocket]

That helps greatly. Thanks for doing what I should have done a better job at in the first place. :-)

[Sam Barrett]

To find a used DVC switch try Bob Anderson in Tampa Fl 813-932-0108