Vacuum advance

[mvent]

Planning ahead and thinking about vacuum advance adjustment. Have my initial and total set and ran out of weather before I could dial in vacuum. I’ve watched Tall John’s video on how he does it, and have read putting vacuum gauge where it can be seen while cruising on flat road and using mighty vac etc. In Tall John’s video he actually moves the distributor at around 2k RPM with vacuum hooked to get highest steady rpm. Wouldn’t doing it his way change initial and total mechanical timing?

 

[Don67Satellite]

Tall John is also doing that to a low compression smogger 440, which tend to respond well to more initial timing. Ask me how I know.

 

[493 Mike]

Planning ahead and thinking about vacuum advance adjustment. Have my initial and total set and ran out of weather before I could dial in vacuum. I’ve watched Tall John’s video on how he does it, and have read putting vacuum gauge where it can be seen while cruising on flat road and using mighty vac etc. In Tall John’s video he actually moves the distributor at around 2k RPM with vacuum hooked to get highest steady rpm. Wouldn’t doing it his way change initial and total mechanical timing?

Yes.
Mike

 

[RJRENTON]

Tall John is also doing that to a low compression smogger 440, which tend to respond well to more initial timing. Ask me how I know.

Out of curiosity, WHO is "Tall John" and why do you believe what he claims is gospel? Never heard of him, another internet wonder??
BOB RENTON

 

[mvent]

Out of curiosity, WHO is "Tall John" and why do you believe what he claims is gospel? Never heard of him, another internet wonder??
BOB RENTON

He is a you tuber, I never said anything about gospel, it was a question, that’s all.

 

[Don67Satellite]

Out of curiosity, WHO is "Tall John" and why do you believe what he claims is gospel? Never heard of him, another internet wonder??
BOB RENTON

No one praising the lord here.

Basically the same kinda old gear head as you find on here with an opinion of how they do stuff.

Since I run a old smog 440 I found his video informative. Don't read more into comments than are really there, Bob.

And, since you asked....

 

[RJRENTON]

He is a you tuber, I never said anything about gospel, it was a question, that’s all.

I don't do u-tube or any other outlets, like X, snap- chat or any of the other "social media" venues......too many self-appointed "experts", trying to explain something they know nothing about.....but this is just my opinion......
BOB RENTON

 

[Don67Satellite]

.....too many self-appointed "experts", trying to explain something they know nothing about.....
BOB RENTON

I hear ya! Ya find 'em everywhere!

 

[Geoff 2]

Is this ported or manifold vacuum?

 

[mvent]

Is this ported or manifold vacuum?

Manifold according to his video.

 

[toolmanmike]

I hear ya! Ya find 'em everywhere!

 

[Geoff 2]

The benefit of manifold vacuum is that it improves the idle because at idle it adds timing. Cruising at 2k rpm, would be no difference whether you had MVA or PVA, both would be active.
If using MVA, it is most important that the idle vacuum is strong enough to fully the VA unit. Not enough vac will result in varying & erratic timing at idle, leading to comments such as 'MVA didn't work for me ' when it was the setting up that was at fault, not MVA. This is why with modified engines, an adj VA unit hould be used.
I do NOT see ANY benefit iin using the method presribed in post #1.
More on MVA benefits:

 

[threewood]

Yep, they are everywhere.

 

[threewood]

The benefit of manifold vacuum is that it improves the idle because at idle it adds timing. Cruising at 2k rpm, would be no difference whether you had MVA or PVA, both would be active.
If using MVA, it is most important that the idle vacuum is strong enough to fully the VA unit. Not enough vac will result in varying & erratic timing at idle, leading to comments such as 'MVA didn't work for me ' when it was the setting up that was at fault, not MVA. This is why with modified engines, an adj VA unit hould be used.
I do NOT see ANY benefit iin using the method presribed in post #1.
More on MVA benefits:

View attachment 1780504

View attachment 1780505

So if I run manifold vacuum and set initial at 22 degrees btdc, how is that different if I set initial timing at 22 degrees btdc using ported?

 

[WileE]

I don't do u-tube or any other outlets, like X, snap- chat or any of the other "social media" venues......too many self-appointed "experts", trying to explain something they know nothing about.....but this is just my opinion......
BOB RENTON

... of course.

 

[gtxrt]

So if I run manifold vacuum and set initial at 22 degrees btdc, how is that different if I set initial timing at 22 degrees btdc using ported?

if you set your timing at idle with the manifold vacuum connected your total timing would be like 20 degrees total and not 34 degrees total.

 

[khryslerkid]

Here we go again!

 

[Geoff 2]

Threewood,
Not quite sure what your question is, so I will answer this way.
When setting the initial timing, the VA should be disconnected whether using MVA or the useless PVA.
So, say you set intial timing at 10* BTDC. Then you connect the VA. If you are using MVA, it will add to the 10*. So if that VA unit has a 22* range, the timing at idle will be 32*. With PVA, connecting the VA will not change the idle timing, will still be 10* BTDC.
Chrys did use MVA through the 1970s; with all the emissions crap, engines ran hotter. Sometimes too hot.....
A temp switch switched VA from PVA to MVA; this increased engine rpm, w/pump & fan speed [ because MVA makes the engine more efficient at idle ]. The engine cooled down.

 

[threewood]

I set both of my cars up using PVA. I use the setting for highest vacuum, and adjust the curb idle down. Very easy to set.

With MVA, to get the same affect at idle you have to set it with the vacuum hooked up. If you have a lopy idle the vacuum changes and so does your initial timing. It seems less accurate.

Just my thoughts.

 

[Geoff 2]

What's that saying.......
You can lead the horse to the water, but you cannot...