460 Straight up Timing Chain upgrade

[ArdWrknTrk]

The thermal valve is a wax pellet that expands inside the threaded in portion
I don't think 'abrupt' is a problem...

What would be good is to determine what each colour means in terms of orifice.
Then you could just use carburetor jets or something else analogous in their stead.

[Gary Lewis]

Maybe "abrupt" is the wrong word.  But the thermostats in our trucks also use a wax pellet and they open up pretty quickly according to my temp gauge.

So far I'm not finding anything that shows what the orifice sizes are.  But this guy said the one on his 'ard wrkn truck is blue.  I'll keep looking.

[Gary Lewis]

12A225 Restrictor assy, (distributor vacuum)

Here are the part numbers so they can be found in a search:
D7AZ 12A225-B  Blue
D9ZZ 12A225-A  Yellow
D6DZ 12A225-A  Red
E1TZ 12A225-A  Orange

And here is the table from the master parts catalog.  Note that this doesn't show the 460, but all of the applications I saw used the blue one for it.  And still no indication of the orifice size.

[Ifitaintbroke]

I ended up having Scotty curve one for me. I've never curved a dizzy and didn't want to mess it up.

[ArdWrknTrk]

Yep, mine is blue.
I think I even have a picture of it...

[Gary Lewis]

I think the only way to figure out what jet to use instead of an actual restrictor is to do it empirically.  But I don't fully understand how the restriction works, so don't know how to go about it.

I would think that restricting the vacuum would just slow the onset of advance, not reduce it.  I say that because in my Parallel Systems class we were taught that you can model a mechanical system with electrical components.  And I would think that a restriction pretty closely aligns with a resistor.  And the voltage on each side of a resistor will be the same unless there is some flow of current.

But in my memory a good vacuum advance doesn't have any leakage, so there shouldn't be any flow.  What am I missing?  There has to be something I'm missing 'cause the restrictors work...  

[ArdWrknTrk]

Empirically, I can take my set of number drills and come close to a size for my blue restrictor.

Whether that's best, for a 300, I can't say. 🧐

[Gary Lewis]

That would be a start.

What I was thinking was to put a dizzy on the bench and connect my Mity Vac to it via a VREST.

[ArdWrknTrk]

Is that going to prove that you can pump fast enough to keep up with the restriction?

Jets are jets.
It's pretty much all about how much it can flow at a given depression.
And that's dependent on the size of the hole. (and how smooth it is)

[ArdWrknTrk]

Have a look at this guy (Mike's) video where I start at about 15:26

Can you see where the water pump was?
Does it look all ribbed with voids behind the impeller?

https://youtu.be/vSWYqpvziEM?si=AG9xjsYUaM-AN2HH

[viven44]

All I can say is the discussion above is quite interesting... If I understand things the right way... can vacuum advance on a distributor can be tuned precisely using a vacuum orifice i.e. recurving it by using less or more vacuum ?

The parallel between electrons and air (or lack thereof) is interesting as well. Voltage equals pressure with which electrons are pushed. Voltage drop would occur across a resistor with current flow. The larger the current flow, the larger the voltage drop. Heat would be dissipated proportional to the amount of voltage drop / current flowing.

With Air, that would mean a restrictor would reduce air pressure past the restrictor, but we are talking vacuum. That means there would be more vacuum (less loss) at the inlet (side connected to VCV), but less air being vacuumed out of the outlet (connected to distributor).

Interested to see what is found out of Gary's experiment

[viven44]

Yep!

I am picking up the water pump plate, timing set from Summit. I am also replacing the water pump with a gates unit. The old water pump and any work done with it, I just don't trust anymore. I am not a parts swapper and hate doing that blindly, but the water pump is $30 and I don't want to go back and re-do any of this for a while.

[ArdWrknTrk]

I can't really blame you.

[viven44]

Agree, for the experiment to work you need a constant source of vacuum that is constantly replenished. The MityVac won't provide that.

[Gary Lewis]

Gary wasn't planning to do the experiment as he's installing seats and painting a console.

But I don't think you can tune a dizzy via a restriction.  I'm back to the electricity analogy - you only have a drop across a resistor/restriction if there is flow through it.  And my experience is that a good vacuum can doesn't leak.  So I'm still at a loss as to how this works.  I'm missing something.  

[ArdWrknTrk]

About the only way you can tune a distributor, is on a Sun machine.

The restriction damps the changing vacuum.
But there has to be some kind of bleed.

[viven44]

I think there will always be some flow, we are talking only 20" Hg or less, which is several orders below absolute vacuum...

Edit: Also what happens when the vacuum advance is not in effect (when throttle is changed).. it has to go somewhere.. does that count as a "bleed"

[ArdWrknTrk]

The diaphragm couldn't resist that.
We're not talking about an electron microscope, it's a dang distributor found in hundreds of millions of vehicles

[ArdWrknTrk]

The springs in the distributor pull the advance back towards zero.
The restriction keeps the plate from being able to move too quickly.
But the restriction also must provide some kind of limit to manifold vacuum.
We see that in how it's implemented in the system

[viven44]

By the way here is Big Blue 2WD’s vacuum diagram. Simplest one I’ve seen. 460/non-AC/no cruise control cab.

Literally every single vacuum control device is present but some things are capped off. EGR is hooked up, no pinging. Maybe it’s stuck open partially. Dist is connected to Ported vac from Edelbrock.

The previous owner and I have hauled and abused this truck this way for a long time. The previous owner even made a round trip from Texas to Washington .. Should I  get it back to how it’s supposed to be ??