Vehicle Emission Control Decal

[dionden]

Hi. Jeff

We have similar vacuum advance setups.

(A) the vacuum restriction goes to port 1

As shown it is farthest from the threaded end of the thermo-valve.

(B) The delay valve is not a V-REST.

I can try to get you a picture of mine if it would help.

Edit: photo of yellow switch valve and blue V-REST

The restriction limits the amount of vacuum reaching the advance diaphragm.

© The point of having an unobstructed path is so that vacuum can be used to control idle speed.

The valve in the thermostat neck will shift to straight manifold vacuum in the event the engine starts to overheat.

This pulls the idle speed up a few hundred rpm (which turns the fan and water pump faster)

This means if the truck were stuck idling in traffic it would make an attempt to cool itself off without much affecting performance off idle.

This is essentially "vacuum logic" that was common before computers and electronics in vehicles.

Good explanation Jim; One thing I noticed is that PVS is on the Rad side of the thermostat, it monitors rad temperature, not engine temperature.

On mine, it had a T with the heater hose, located on the intake manifold until I did away with it. I think some EFI engines are set up in such a way.

 

[ArdWrknTrk]

Good explanation Jim; One thing I noticed is that PVS is on the Rad side of the thermostat, it monitors rad temperature, not engine temperature.

On mine, it had a T with the heater hose, located on the intake manifold until I did away with it. I think some EFI engines are set up in such a way.

Yes, it's in the 'neck' where the upper radiator hose attaches.

So it senses heat after any thermostat restrictions.

It is basically a wax pellet that has a calibrated coefficient of expansion pushing open a shuttle port.

The heater is always run in a closed bypass loop (it avoids the thermostat and radiator)

This gets heat to the cab -and the throttle body- ASAP while allowing the thermostat to function getting the block/engine up to operating temperature.

[Gary Lewis]

Yes, it's in the 'neck' where the upper radiator hose attaches.

So it senses heat after any thermostat restrictions.

It is basically a wax pellet that has a calibrated coefficient of expansion pushing open a shuttle port.

The heater is always run in a closed bypass loop (it avoids the thermostat and radiator)

This gets heat to the cab -and the throttle body- ASAP while allowing the thermostat to function getting the block/engine up to operating temperature.

Jim - In my experience "ASAP" is relative to the engine you have. My aluminum 3.5L EB seems to warm up fairly quickly, but a 7.5L 460 is a big lump of iron so ASAP ain't very fast. But yes, the heater gets the warmed water before the radiator does.

Jeff - You've been running around w/o vacuum advance? This should make a noticeable difference in MPG.

[ArdWrknTrk]

Jim - In my experience "ASAP" is relative to the engine you have. My aluminum 3.5L EB seems to warm up fairly quickly, but a 7.5L 460 is a big lump of iron so ASAP ain't very fast. But yes, the heater gets the warmed water before the radiator does.

Jeff - You've been running around w/o vacuum advance? This should make a noticeable difference in MPG.

Everything is relative.

The 460 is a bigger lump of iron than Jeff's 351.

As Soon As Possible doesn't mean "fast" it just means heat has priority over the block.

Yes. It sure seems ridiculous that Big Brother had no vacuum advance (and I wonder where the static timing was set)

When I find hidden stuff like this I want to throttle someone!

Hopefully Jeff can get a proper V-REST.

He'll notice power as well as economy since that's why vacuum+mechanical advance is installed.

[Gary Lewis]

Everything is relative.

The 460 is a bigger lump of iron than Jeff's 351.

As Soon As Possible doesn't mean "fast" it just means heat has priority over the block.

Yes. It sure seems ridiculous that Big Brother had no vacuum advance (and I wonder where the static timing was set)

When I find hidden stuff like this I want to throttle someone!

Hopefully Jeff can get a proper V-REST.

He'll notice power as well as economy since that's why vacuum+mechanical advance is installed.

Yup, hidden stuff is no fun.

But you are right, Jeff is going to be happy.

As for relative, our temp today of 100F is relative - it is hotter in Phoenix, but then they don't have much grass left to mow and I do.

[BigBrother-84]

Yup, hidden stuff is no fun.

But you are right, Jeff is going to be happy.

As for relative, our temp today of 100F is relative - it is hotter in Phoenix, but then they don't have much grass left to mow and I do.

Gentlemen, thanks a lot!

So my proposed setup isn’t stupid, yeah!

Thanks to Jim, the parallel unobstructed tube now makes sense. Interesting AND logical 🖖.

So, next step is to find a Vacuum Restrictor. With a good picture, I’ll probably find one at my local salvage yard.

Question:

Considering that Big Bro starts and idle very well, does he a need timing adjustment (I’m not equipped for, so a garage job).

[ArdWrknTrk]

Gentlemen, thanks a lot!

So my proposed setup isn’t stupid, yeah!

Thanks to Jim, the parallel unobstructed tube now makes sense. Interesting AND logical 🖖.

So, next step is to find a Vacuum Restrictor. With a good picture, I’ll probably find one at my local salvage yard.

Question:

Considering that Big Bro starts and idle very well, does he a need timing adjustment (I’m not equipped for, so a garage job).

Be careful what garage you deal with.

Finding one with a 1/2" distributor wrench could prove a challenge!

Obviously, at some point someone felt they could get over on you and hide their "handiwork".

I looked at my V-REST and couldn't easily find an engineering number to help your search. (they are tiny)

Maybe Gary has information in 'The Tower'?

I'm quite sure Big Brother will need some distributor adjustment once the vacuum is working (if the unit in there now even holds vacuum)

When idling my Crane adjustable advance easily pulls in 20° on top of 12° static.

32-36° is not unusual for these engines.

 

[BigBrother-84]

I'm quite sure Big Brother will need some distributor adjustment once the vacuum is working (if the unit in there now even holds vacuum).

Jim, the distributor unit seems to hold vacuum.

I made

, creating some vacuum (with my mouth ), and the engine rpm accelerate.

 

[ArdWrknTrk]

I'm quite sure Big Brother will need some distributor adjustment once the vacuum is working (if the unit in there now even holds vacuum).

Jim, the distributor unit seems to hold vacuum.

I made

, creating some vacuum (with my mouth ), and the engine rpm accelerate.

That's great news!

I typically use my MityVac brake bleeder to test vacuum "hg and operate things like distributors and HVAC controls.

Hopefully it's easy to get dialed in once you get everything connected.

[Gary Lewis]

I looked at my V-REST and couldn't easily find an engineering number to help your search. (they are tiny)

Maybe Gary has information in 'The Tower'?

Oddly enough I cannot find a calibration code for an '84 F350 w/a 351W 4bbl. But there is one with a 351W 2bbl. The Canadian version w/a manual tranny is Parts List #302 and it has a "D7AZ 12A225-B Restrictor assy, (distributor vacuum) Color code: Blue". That part is used in many, many of the applications, including #399 & 400 which are 351W's with 4bbls. So I think that's the one you need, Jeff.