Thermostatc vacuum switch

[shelbydoug]

Not just at idle. Any time the throttle is closed the vacuum signal to the distributor drops to a lower value, regardless of RPM. Decelleration for example. The only time the distributor vacuum advance would see manifold vacuum is during an overheat situation if it is all working properly.

No boiling water yet!

If it works the way I think it is supposed to, I actually like the idea of it closing the vacuum to the vacuum advance at idle.

It gives me tuning options.

Also I THINK that it switches at some point from engine vacuum to timed port vacuum. That's really what the question initially was getting at.

Either way, I'm ok with it. I probably will need to do the hot water thing to determine at what temp it opens and if it is simgle stage or dual.

I like the idea that it is still installed in the original thermostat housing. It is appropriate for a '68.

Now if I can only find a yellow plastic overlay for the ignition coil, like the battery top idea, I'd be happier.

Unfortunately, although looking great, the Marti Autolite spark plug wires crapped out already. Too bad. They looked great in the AUTOLITE cap.

I haven't thought about the original spark plug wires in 45 years. I was innocent then. I never realized how FREAKIN' BAD the original wire engineering was back then? 

That's ok with me. I don't see any disadvantage to that function.

[Corey Bowcutt]

This has been a very interesting and informative thread.  I have a related question.  If you have electronic ignition does the vacuum advance still function?  I understand having it all hooked up to look correct but was wondering if it is actually doing anything?

Corey

[Royce Peterson]

Electronic ignition (Pertronix etc) replaces the ignition points as a method of charging and discharging the coil. It has no effect on anything controlled by vacuum.

This has been a very interesting and informative thread.  I have a related question.  If you have electronic ignition does the vacuum advance still function?  I understand having it all hooked up to look correct but was wondering if it is actually doing anything?

Corey

[shelbydoug]

Electronic ignition (Pertronix etc) replaces the ignition points as a method of charging and discharging the coil. It has no effect on anything controlled by vacuum.

This has been a very interesting and informative thread.  I have a related question.  If you have electronic ignition does the vacuum advance still function?  I understand having it all hooked up to look correct but was wondering if it is actually doing anything?

Corey

+1.

[shelbydoug]

There are several hook up diagrams in the 68 Shop Manual.

By trial and error, I have determined that the engine vacuum goes on the bottom, the line to the carb "timed vacuum" is in the middle and the distributor vacuum advance goes on top.

If you put the distributor vacuum advance in the middle as the engine gets hot it will advance the distributor and raise the idle rpm about 400 rpms.

For me that doesn't work.

The tree seems to open at around 160 water temp. Apperently it is two stage? I don't know at what temp the valve distributes vacuum to the vacuum advance. I haven't gotten hot enough yet.

[mr68shelby]

Just found that The March 1967 Shop Tips has a page on these. It references the 1967 valves which have a different design, but they should operate the same. It says the thermal valve opens at approximately 230 degrees to switch from the carb vacuum to the intake vacuum. Mike

[shelbydoug]

Just found that The March 1967 Shop Tips has a page on these. It references the 1967 valves which have a different design, but they should operate the same. It says the thermal valve opens at approximately 230 degrees to switch from the carb vacuum to the intake vacuum. Mike

Is there a '67 version of the vacuum tree? I'm pretty sure the switch over temp on mine is much lower then that?

[J_Speegle]

Is there a '67 version of the vacuum tree? I'm pretty sure the switch over temp on mine is much lower then that?

For non-HipPo 289 applications. Its integrated with heater hose intake manifold connection. There has been one for sale for over a year on Ebay




Since its not factory might as well swap out the thermostat housing and use one from a different year it you choose to go that route

[shelbydoug]

Is there a '67 version of the vacuum tree? I'm pretty sure the switch over temp on mine is much lower then that?

For non-HipPo 289 applications. Its integrated with heater hose intake manifold connection. There has been one for sale for over a year on Ebay




Since its not factory might as well swap out the thermostat housing and use one from a different year it you choose to go that route

I presume that they are very rare and as such the price of them is excessive?

I actually like the way that mine works on my 68.