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| vacuum adv can shopping https://www.slantsix.org/forum/viewtopic.php?t=12931 |
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| Author: | sixsignet [ Wed May 11, 2005 10:20 am ] |
| Post subject: | vacuum adv can shopping |
I have a 72 electronic distributor and I'm looking for an 8 to 10 degree vacuum advance pod (4 or 5 stamped on arm). Just got back from visiting a few parts stores and not finding any. I had them look in the book. What models/years should I have the guys look up to get this ?  This is the first time I've done a recurve, and I thought getting vacuum pods with different advance ranges was no big deal... |
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| Author: | Slant6Ram [ Wed May 11, 2005 11:05 am ] |
| Post subject: | might help? |
I went searching a few weeks back, but could only find 2 options for advance cans. I found only 3 available choices at Advanced Auto Parts: The late 70's aspen had an 11 can (stamped 11 on the arm) The early 70's dart had a 6.5 stamped on the arm (adjustable tension) And another choice at 6.5 (fixed tension) I entered the part #'s into the parts database here , so you should be able to find them easily if they are of interest. If nothing else, it will help you to know what -NOT- to order, since the stores catalog had no information about what amount of advance went with each part #. |
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| Author: | Dart270 [ Wed May 11, 2005 11:25 am ] |
| Post subject: | |
Standard Ignition makes them, at least did a few years back, and had 6.5 - 11 with a few in between (8.5, 9, 10.5?). My advice is to use something between 9 and 11 with less mechanical advance (weld up advance slots or get a late 70s dist with less advance built in). This generally gives better power and mileage than the early setups. Lou |
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| Author: | sixsignet [ Wed May 11, 2005 11:51 am ] |
| Post subject: | |
I had the guys look in actual books, but they seemed lost. What can I say to direct them to finding this range of cans? Lou - when you say between 9 and 11, those would have 4.5 and 5.5 stamped on the arms, right? |
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| Author: | Dart270 [ Wed May 11, 2005 1:07 pm ] |
| Post subject: | |
Any Standard ignition book should have several part numbers/pictures, but may not list the advance spec. You may have to open boxes up (or get them or warehouse) to see the stamping. Nope, I mean stamped 9-11 (18-22 crank degrees). You want a lot of vac advance for best mileage. Lou |
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| Author: | sixsignet [ Wed May 11, 2005 1:51 pm ] |
| Post subject: | |
That would be too much, I think. I'm starting out at 15 degrees btdc at idle. This distributor came with a 17 (8.5 stamped) degree can and had 30 degrees mechanical. I have filled in the slots to give it only 14 degrees mechanical and set the initial timing at 15 degrees. Currently I have the original 17 degree can tightened up about 8 turns ccw. I have been adjusting it 1/2 turn ccw after each drive test. It has very nice pickup and cruising, but falls flat on its face when I try to accelerate sharply from a 25 or 45mph cruise. I just tested it with the vacuum can modified so that it's about 11 or 12 degrees and it runs better now. My mod: The arm goes through an opening in the back of the can to attach to the diaphram. The arm has shoulders that are bigger than the opening and that limits the arm's travel. I contact cemented some cardboard shims to the edge of the opening to reduce the travel about 40 percent. Oops. Sorry rust collector. I was editting this while you were answering. |
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| Author: | Rust collector [ Wed May 11, 2005 2:07 pm ] |
| Post subject: | |
That sounds like it would work to me... |
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| Author: | SlantSixDan [ Wed May 11, 2005 2:53 pm ] |
| Post subject: | |
A '72 electronic \6 distributor is a rarity..."officially" they didn't exist til '73. The electronic distributors' pickup plates are double-drilled so you can use either the early or late style vacuum cans. The early cans tend to have less advance, so you may want to try something like a NAPA Echlin VC1130 or VC1225. The Standard-Bluestreak catalogues used to have very good can-by-can specs in them, but I don't have any currently that do. |
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| Author: | sixsignet [ Wed May 11, 2005 3:00 pm ] |
| Post subject: | |
http://www.slantsix.org/forum/viewtopic ... cs&start=0 Well, it was advertized on Ebag as 72. It is the Rolik Distributor discussed in the "Distributor recurve - pics" post linked above. Thanks for the tip about the double-drilled plate. |
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| Author: | SlantSixDan [ Wed May 11, 2005 3:27 pm ] |
| Post subject: | |
Oh, one of Bill R's units? OK, probably a 3755042, which is a '73 unit. |
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| Author: | Eric W [ Wed May 11, 2005 8:53 pm ] |
| Post subject: | |
For what its worth, I pulled a vacuum can off a '74 Dart today that was stamped 8.5. Its the same as what I have now, but it came out of my old '72 points distributer. |
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| Author: | Slant6Ram [ Thu May 12, 2005 6:26 am ] |
| Post subject: | Fance |
Quote: I contact cemented some cardboard shims to the edge of the opening to reduce the travel about 40 percent.
I have considered doing the same thing. You'll have to let us know how it works. Fabrication is our friend, since the aftermarket for slant six stuff can be a little sparce.
Quote: Currently I have the original 17 degree can tightened up about 8 turns ccw
I suspect you will now be able to reduce some of that tension to help get the vacuum advance in quicker.
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| Author: | sixsignet [ Thu May 12, 2005 12:04 pm ] |
| Post subject: | shim works, but I think I misunderstood problem |
I think I need to stay with the 17 degree can and continue to tighten its spring. After adding the shims to the vacuum adv can the hesitation went away, but I think I'm probably not getting enough advance during cruising now. This is my first attempt recurving distibutors or even thinking about the whole timing curve, so it's still hard to believe that 40-45 degrees advance is safe for the engine during cruising. Add to that the fact that it is really hard for me to hear "pinging" on my slant becuase of the headers and dual pipes, and I'm extra paranoid about too much advance on the freeway. SHIMS: This seems to work. I only had to stack 2 rectangles of card stock on one side of the opening because the arm can't skew to one side because its angle is secured by the pin in the plate. You could probably fine tune the advance using layers of thin gasket material and a hand vacuum pump. |
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| Author: | Dart270 [ Thu May 12, 2005 1:08 pm ] |
| Post subject: | |
I don't understand why you should be getting hesitation from the vac advance setting. As soon as you get on it reasonably hard, the vac advance should pull off immediately and you should be left with only mech advance. Maybe the vac advance can responds slowly, or is hanging up? Do you get the hesitation when you disconnect the vac advance? Engines at part throttle cruise have quite low cylinder pressure due to the small amount of air/fuel being let in to fill the cyl. That's why they can stand (and really want) a lot of timing advance. I shoot for between 45 and 50 total (28 mech + 22 vac) at cruise. V8s probably want even more, like 50-55. I've found that the difference between 45-50 and just mech (around 28 deg, no vac) is 10-20% in MPG. Not bad for a $15 part... Lou |
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| Author: | sixsignet [ Thu May 12, 2005 4:49 pm ] |
| Post subject: | Retarded - me or the timing? |
When I hit the pedal and hold it (from a 30mph cruise) it hesitates, coughs or even backfires through the carb (I think the carb - a muffled pop). I tightened the can 12 turns CCW and symptom is practically gone. But I wondered if the vacuum adv was advancing during cruise. Then I started checked everything I could. It turns out I'm getting less than what I expected to get from centrifugal and vacuum advances. I strapped the vacuum tester gauge to the wiper arm and connected it with a tee to the ported vacuum. I got 15" to 16" vacuum at cruising speed and it drops to 5" or less when I try to accelerate quickly. I know I have high manifold vacuum at idle, so I checked it and it is 17". I connected the vacuum advance can (only - instead of the pcv valve) to the manifold vacuum hose and started it up: it only moved the timing mark 5 degrees. So I have the 17 degree can so tight it only gives 5 degrees at 17" vacuum. Then I reconnected the hose to the pvc valve and plugged the ported vacuum line so I only had centrifugal advance. Centrifugal advance is only 7 degrees at 2100. It should be 9 or 10 before the pin contacts the long loop on the heavy spring. Maybe I just need to adjust this loop to get 2 more degrees. But it doesn't change at 2400rpm, so I think the second spring is too heavy. Where do you get the springs for the distributor? Are they the same as the ones for GM V8s? |
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