Lost and cornfused

[Hstrymkrs]

I can remember working the graveyard shift back in the '70's. Then leaving to get to high school.

It's tough if it is not your regular routine.

Vacuum advance allows you to factor throttle position and engine load on top of simple centrifugal advance that is determined by engine rpm, weights and springs.

It allows for more advance at lower rpm while being able to control knock.

If your new carb is a Holley clone it should have ports for both timed (ported) vacuum and manifold vacuum.

Gary has already graciously offered to draw it all up

Thanks. I was just reading about the carb we bought and how it is set up to get a better understanding. Do I understand correctly that manifold is the better of the two to route the vacuum line?

[ArdWrknTrk]

Thanks. I was just reading about the carb we bought and how it is set up to get a better understanding. Do I understand correctly that manifold is the better of the two to route the vacuum line?

Gary prefers ported.

For good reasons, especially **for someone that has** an automatic.

Ford used restricted manifold vacuum with the stock DSII systems

**Edit**

[85lebaront2]

While looking through the fog, my initial thought is that it looks like it will work. I do not recover well from night shift so please forgive any errors I make. However, I will need to pull out my Acme Wiley Coyote work bench to find out for sure. I will call DUI back and ask them about the vacuum. It wasn't a matter of want or not want, it was a matter of it not being their currently and if I needed to route a vacuum line to the distributor. I will make the inquiry. I understand that the vacuum advance allows the engine to conserve energy so to speak when not under load. Again, I have no problem with a vacuum advance, I just wasn't sure how I would work it in and if I "needed" it. I wonder if DUI would program a better learning curve into my brain.

I too have worked rotating shifts and can fully understand the "fog" night shift, unless like some I worked with who preferred it is alien to human nature, vampires and zombies, no.

Vacuum advance, easiest way to describe it, it makes up the difference in what the engine can handle under load and what it can handle unloaded or lightly loaded. Performance (racing) engines use either a fixed advance or only a centrifugal (rpm varied) advance system. For years, that was all that was put on cars once automatic advance systems were introduced, other than Ford. Ford used a centrifugal advance with fairly light springs and vacuum brake system. The vacuum brake was a spring loaded piston connected to the intake manifold vacuum and a disc on the movable portion of the centrifugal advance that the brake held back. Higher manifold vacuum would retract the piston and allow the spark to advance more. Chevrolet added an external vacuum diaphragm to the "floating" distributor body which it rotated for more advance.

When Ford and Holley started working together in the late 40s, Holley developed the "Load-a-matic all vacuum advance system, no mechanical advance weights or springs. These required either a spark control valve or a check ball so the very weak venturii signal didn't leak, but the stronger ported spark signal was still available. These distributors had a large fairly flat vacuum chamber and two angled springs on the breaker plate.

FWIW, (a) Mallory Rev-pol distributors and some of the offshoots of them use the old Ford vacuum brake system (b) GM distributors have one of the easiest mechanical advance systems to re-curve, it's right under the rotor. If DUI uses the Ford style vacuum advance can, it is easily adjusted with a 1/8" Allen wrench.

Your Carter or Holley or Motorcraft one barrel should have a manifold and ported vacuum source on it. Ford usually prefers ported spark, but not always, try both after setting the initial timing the way DUI says, then see which way it runs and drives better.

[Steve83]

Thanks. I was just reading about the carb we bought and how it is set up to get a better understanding. Do I understand correctly that manifold is the better of the two to route the vacuum line?

What do the distributor instructions say to connect it to?

[Hstrymkrs]

What do the distributor instructions say to connect it to?

It is in transit to the house. I will post the answer once it arrives.

 

[Steve83]

It is in transit to the house. I will post the answer once it arrives.

Have you tried downloading it from the mfr.'s website?

[Gary Lewis]

Have you tried downloading it from the mfr.'s website?

Good idea. Here's a link to the Street/Strip Ford DUI distributor. May not be the right one, but it has several points:

• They say you "must" remove the ballast resistor in the wiring harness and run a 12 gauge wire to the "BATT" terminal

• They recommend manifold vacuum as "This vacuum advance will keep your plugs cleaner. If your car does not run good at manifold vacuum, then connect it to ported vacuum."

• They suggest gapping the plugs at .050" to .055" "now that you have enough firepower available"

• They recommend setting the initial timing to 12 degrees BTDC while idling below 600 RPM and with the vacuum hose pulled off the advance and plugged.

[1986F150Six]

Good idea. Here's a link to the Street/Strip Ford DUI distributor. May not be the right one, but it has several points:

• They say you "must" remove the ballast resistor in the wiring harness and run a 12 gauge wire to the "BATT" terminal

• They recommend manifold vacuum as "This vacuum advance will keep your plugs cleaner. If your car does not run good at manifold vacuum, then connect it to ported vacuum."

• They suggest gapping the plugs at .050" to .055" "now that you have enough firepower available"

• They recommend setting the initial timing to 12 degrees BTDC while idling below 600 RPM and with the vacuum hose pulled off the advance and plugged.

Jonathan [FordF834] has a Duraspark distributor [not HEI, though] which was sold and set-up by Performance Distrbutors in TN. It was used in my truck for years and is now providing reliable service for his truck.

Gary, it is the one you worked with when "dialing in" my truck.

[85lebaront2]

Good idea. Here's a link to the Street/Strip Ford DUI distributor. May not be the right one, but it has several points:

• They say you "must" remove the ballast resistor in the wiring harness and run a 12 gauge wire to the "BATT" terminal

• They recommend manifold vacuum as "This vacuum advance will keep your plugs cleaner. If your car does not run good at manifold vacuum, then connect it to ported vacuum."

• They suggest gapping the plugs at .050" to .055" "now that you have enough firepower available"

• They recommend setting the initial timing to 12 degrees BTDC while idling below 600 RPM and with the vacuum hose pulled off the advance and plugged.

Gary, FWIW, using the power harness for the TFI eliminates the ballast resistor from the equation. The #12 wire though, is what drives you to using a relay to power the DUI system. This was the point I was making several posts back about the HEI being a power hog. Are you (I can't look at the diagram right now) recommending going from the battery terminal of the starter relay? I think I would use the nice battery source on the driver's side, the insulated stud. That would put everything fairly close to the existing ignition system wiring and the new distributor.

If he can find a relay cover like the trailer package and DRW trucks used I'm sure he could stick the relay under there. If not, maybe one of the Bosch relays with a mounting tab so it can be installed right side up (terminals down) as Steve points out they are pretty weatherproof if somewhat protected from the worst conditions.

The .050 - .055 gap sounds about right for an HEI system, I don't have tune-up specs for anything that old my information starts at 1982, Chevy that year was .045 gap, but the Oldsmobile 307 was .060 gap.

Manifold vacuum was what most GM engines used until the first emission systems in 1968 and I know that ported spark and Chevrolet engines did not play well together, yet Chrysler used ported spark with no issues, but their static timing was as high as 12.5° BTDC on the big blocks, Chevy was on the order of 4-6° BTDC on most engines.

[Gary Lewis]

Gary, FWIW, using the power harness for the TFI eliminates the ballast resistor from the equation. The #12 wire though, is what drives you to using a relay to power the DUI system. This was the point I was making several posts back about the HEI being a power hog. Are you (I can't look at the diagram right now) recommending going from the battery terminal of the starter relay? I think I would use the nice battery source on the driver's side, the insulated stud. That would put everything fairly close to the existing ignition system wiring and the new distributor.

If he can find a relay cover like the trailer package and DRW trucks used I'm sure he could stick the relay under there. If not, maybe one of the Bosch relays with a mounting tab so it can be installed right side up (terminals down) as Steve points out they are pretty weatherproof if somewhat protected from the worst conditions.

The .050 - .055 gap sounds about right for an HEI system, I don't have tune-up specs for anything that old my information starts at 1982, Chevy that year was .045 gap, but the Oldsmobile 307 was .060 gap.

Manifold vacuum was what most GM engines used until the first emission systems in 1968 and I know that ported spark and Chevrolet engines did not play well together, yet Chrysler used ported spark with no issues, but their static timing was as high as 12.5° BTDC on the big blocks, Chevy was on the order of 4-6° BTDC on most engines.

David/1986F150Six - Yes, I remember that distributor. And it really helped Jonathan's truck when he installed it to replace his worn-out one. (Which is an interesting point as we cuss and discuss buying a new vs used distributor.)

Bill/85lebaront2 - I understood what you were saying about the HEI being a power hog. It saturates that coil with lots of current, which is what gives it such a hot spark. (Remember when they first came out and a burned distributor cap or rotor was par for the course?)

But I don't know of the "nice battery source on the driver's side, the insulated stud". I'm not familiar with that source, but it would certainly simplify things to have power closer to where the relay may need to be. Can you provide a pic or show it somehow?

And I agree about the relay cover. I'd been saving that bit until last, until we get the wiring sorted out. But I'm not sure that a Bosch relay fits in/under that cover very well. So some research is needed to come up with a neat solution since the page I'm thinking about needs to cover all the issues.