Ported Vaccuum?

[timsweet]

Going from a 2bbl to a 4 bbl cab and I need to know if the distributor needs ported vacuum?

Tim

 

[wwhite72]

MY swap from oem 2V to 4V involved the factory intake replaced with an Edelbrock intake, both of which use a vac connection tapped in the forward area of the intake. That was how Ford designed it and always worked just fine with my new Holley and factory dist.

 

[timsweet]

There are to vacuum ports on my new Edelbrock carb. One is time/ported the there is not. It designed handle the the distributor vacuum...just double checking which one I need to connected up to.

MY swap from oem 2V to 4V involved the factory intake replaced with an Edelbrock intake, both of which use a vac connection tapped in the forward area of the intake. That was how Ford designed it and always worked just fine with my new Holley and factory dist.

 

[73pony]

I have had better luck running my vac advance on the ported vac. Other opinions differ.

 

[wwhite72]

73pony is right. lots of opinions. I believe GM used ported and Ford used constant and that is why aftermarket carbs have both available. I left both plugged on the Holley and used intake port because it looked original.

 

[Stanglover]

I just did a bit of checking by Googleing Mustang vacuum systems. I'm not sure how to add the diagram, sorry. www.allfordmustangs.com/forum/attachments/classic-tech/344298d1399590285-19 . OOPs, that link no longer works, just Google it.

As I understand it. most, if not all 351C's had a distributor vacuum control valve with a dual vacuum distributor. The hose that went to the manifold port was connected to the bottom port on that valve and the hose was T'd into the rear retard port on the dizzy vac can. The advance hose connected to the top in and out ports and then to the carb. I don't think the Autolite carbs had timed ports back in the day, but then the initial was only set at 6* on most 351C. We are talking about a 351C aren't we???

I have my Holley 4160 4V connected to timed vacuum. I no longer use the retard valve, don't really need it in our climate, so the manifold port is plugged as is the vac. port at the base of the Holley. I have good control of the timing with it set like this. It only seems to need mechanical timing at idle @14* . That's my story and I'm sticking to it!! lollerz

Timing has been gone over tons of times and opinions differ as much as the weather, but I found very useful info at www.bob2000.com/dist.htm Timing tips for Ford distributors. Kind of explains in simple terms which I needed for sure.

Hope this helps,

Geoff.

 

[Mikes73]

I also use ported vacuum, to me it makes for a more predictable steady idle especially with an automatic transmission when going from park to drive.

 

[Stanglover]

I also use ported vacuum, to me it makes for a more predictable steady idle especially with an automatic transmission when going from park to drive.

Right on Mike!

 

[Mikes73]

Thanks Brutha! I hook it up to the left port on the Eddie carb Tim.

 

[timsweet]

Thanks everyone. Ported Vacuum it is. At some point I'm going to diagram it all out - to include the A/C vacuum unit for when the car is at idle....if it's needed.

 

[72HCODE]

ported for our cars is how it came from the factory, you can retune for Full manifold vacuum if wanted.

Ported vacuum means, ZERO vacuum to the vacuum advance at idle RPMs.

full manifold vacuum means what ever the idle Vacuum is will be acting on the vacuum advance.

what this means is:

with ported vacuum the vacuum advance is Turned off at Idle rpms. this lowers timing at idle which increase exhaust temperature, this reduces emmisions at idle(when sitting in traffic)

this means when you stomp on the pedal first Vacuum turns on and advances the vacuum advance however under heavy acceleration vacuum will be low and thus the advance will basically shutdown again until vacuum picks up at cruise speed.

with full manifold vacuum the vacuum advance is on and engine timing is advanced, when you stomp on it the engine will be at a higher timing already resulting in more off the line power then the vac drops and the advance drops and again vaccum will catch up at cruise speed.

this is why people like full manifold vacuum because you get more off the line power at the cost of higher emissions.

the big thing to watch out for in going from ported to full on the advance is ping/detonation you have to see what your engine will tolerate and take initial timing out or recurve the distributor at different points. it is more trial and error with each engine individually. basically the performance guys want to take the engine right to the edge of lean on the entire throttle to make more power, the guys that drive in traffic want good all around performance.

having the exhaust at a higher temperature not only reduces emissions but can benefit daily driving where the environment is not always 75F ,sunny, with low humidity.

it is a trade off.

if your car must pass emissions inspection then this can be a problem converting over to full manifold vacuum.

 

[wwhite72]

I believe I have seen at least 4 different vac hose diagrams for 72 351c's depending upon if it is 2v, 4v, auto, manual, ac/non-ac ....and of course if it was a california car. I also dont know if the autolite 2100 on my car even had a dist advance port. I do know that my engine had open chambers and the factory specs for tuning resulted in a car that ran so badly and was so underpowered that the initial advance had to be so low so that it wouldn't ping sitting being driven off the lot, had less than 200hp, and even had to have a throttle position solenoid installed just so you could turn the car off without it running on forever. So while yer 4v CJ may have had hoses going one way, mine was different.

 

[timsweet]

Awesome coverage!!!! Thanks

ported for our cars is how it came from the factory, you can retune for Full manifold vacuum if wanted.

Ported vacuum means, ZERO vacuum to the vacuum advance at idle RPMs.

full manifold vacuum means what ever the idle Vacuum is will be acting on the vacuum advance.

what this means is:

with ported vacuum the vacuum advance is Turned off at Idle rpms. this lowers timing at idle which increase exhaust temperature, this reduces emmisions at idle(when sitting in traffic)

this means when you stomp on the pedal first Vacuum turns on and advances the vacuum advance however under heavy acceleration vacuum will be low and thus the advance will basically shutdown again until vacuum picks up at cruise speed.

with full manifold vacuum the vacuum advance is on and engine timing is advanced, when you stomp on it the engine will be at a higher timing already resulting in more off the line power then the vac drops and the advance drops and again vaccum will catch up at cruise speed.

this is why people like full manifold vacuum because you get more off the line power at the cost of higher emissions.

the big thing to watch out for in going from ported to full on the advance is ping/detonation you have to see what your engine will tolerate and take initial timing out or recurve the distributor at different points. it is more trial and error with each engine individually. basically the performance guys want to take the engine right to the edge of lean on the entire throttle to make more power, the guys that drive in traffic want good all around performance.

having the exhaust at a higher temperature not only reduces emissions but can benefit daily driving where the environment is not always 75F ,sunny, with low humidity.

it is a trade off.

if your car must pass emissions inspection then this can be a problem converting over to full manifold vacuum.

 

[Odmark]

When i hook my dist up to full vacuum my ignition timing instantly jumps to about 40 degrees btdc at idle so i use the ported port :huh:

 

[Stanglover]

Our Tech Advisor, 72Hcode, has just written one of the best explanations on timed ported versus manifold ported advance I've read here. I've struggled to get a full understanding. Many have tried to explain it, but this clears it up for me.

However, I really do think that the reason why so many have issues with too much advance on STOCK distributors is the fact that most have the wrong mechanical advance built into them. I realize that there are different requirements between auto and manual trans., but my engine would not tolerate anything over 36* mechanical total. With an L15 slot plate on my reman. dist., 30 degrees on the crank, I could add no more than the factory 6* initial and it was a dog at that. In my case, I pulled the thing apart and welded the plate and recut it to equal an L10 slot or 20* crank. Then I found that it would run great with 14* initial. I guess what I'm saying is that many seem to be trying to get perfect timing with a distributor that is not made for it. I actually want to try adding a plastic sleeve (from a Duraspark) to the stop pin to cut the mechanical down even further, but then add the difference to the initial and see what that does. If no benefit, it will be easy to go back to where it was.

Comments?

Geoff.

 

[Stanglover]

I believe I have seen at least 4 different vac hose diagrams for 72 351c's depending upon if it is 2v, 4v, auto, manual, ac/non-ac ....and of course if it was a california car. I also dont know if the autolite 2100 on my car even had a dist advance port. I do know that my engine had open chambers and the factory specs for tuning resulted in a car that ran so badly and was so underpowered that the initial advance had to be so low so that it wouldn't ping sitting being driven off the lot, had less than 200hp, and even had to have a throttle position solenoid installed just so you could turn the car off without it running on forever. So while yer 4v CJ may have had hoses going one way, mine was different.

I think you're right, there are many variations of vacuum hose combinations depending on the year, options, emissions, etc. etc. Just finding the correct one can be the issue, then sorting out what you really need. If I'm right, the basic requirements are the same, but it's all the option stuff that gets in the way. Not many of us run 351C's 2V or 4V as they were shipped from the factory, so my thinking is that it comes down to researching what we need and don't need, then customizing the hoses to suit.

Yes, no , maybe??

 

[timsweet]

I think you're right, there are many variations of vacuum hose combinations depending on the year, options, emissions, etc. etc. Just finding the correct one can be the issue, then sorting out what you really need. If I'm right, the basic requirements are the same, but it's all the option stuff that gets in the way. Not many of us run 351C's 2V or 4V as they were shipped from the factory, so my thinking is that it comes down to researching what we need and don't need, then customizing the hoses to suit.

Yes, no , maybe??

Exactly. Originally the 72 351c (in my 73) had the EGR in place and working, but the solenoid for A/C pause during idle wasn't connected. Diagrams show that solenoid in two different places, upfront on the drivers side of the block or in the rear on the right side of block. Of course there's different routing for each location.

Now take the fact that I've changed the intake manifold and there is no EGR and I've added at 4bbl carb with multiple locations for vacuum (better than not enough!!).

Working on figuring that all out. Thanks for all the insight....you all rock!!!

 

[Odmark]

Since we are on the subject, does anyone know why my dist does that? Instantly going to 40° when att full vacuum.

When i hook it up to my ported slot i think i have it set up about 16 initial and 36 total. And i can adjust the total timing at the vacuum canister.

But at full manifols vacuum its just 40 initial and wont move at all when adjusting.:huh:

 

[TommyK]

Since we are on the subject, does anyone know why my dist does that? Instantly going to 40° when att full vacuum.

When i hook it up to my ported slot i think i have it set up about 16 initial and 36 total. And i can adjust the total timing at the vacuum canister.

But at full manifols vacuum its just 40 initial and won't move at all when adjusting.:huh:

It is because when you hook the vacuum advance up to a vacuum source below the throttle blades it sees vacuum as soon as the engine is running.

Therefore whatever advance the vacuum can will allow is immediately pulled in and increases your initial timing.