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Duraspark II Distributor Issue


19Walt93

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The way Ford set it up the retard side would get vacuum at idle. If you leave the retard side vacuum port open it will function like a normal vacuum advance and that will improve low rpm throttle response and power. If you cap the retard port that will restrict the advance side because vacuum will be trying to pull it toward advance and the retard side will resist movement because no air can get in behind the diaphragm.
What is overrun?
 


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Uncle Gump

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I was just working on an update for the Tech Library to cover the dual vacuum port distributer for use when doing a dura spark conversion.

I actually have a couple question that you folks... @19Walt93 or anyone else might help me with.

I know this was an emission related addition at some point. I'm thinking it may have been for colder climates. But diving into the web a bit I've seen several references that the second port was actually connected to a thermo vacuum switch. When cold... vacuum would be applied to the second vacuum reference port on the distributor. This would actually try to retard the timing (it looks to me that the reference ports are on opposite sides of the diaphragm). Manifold vacuum would also be applied to the original port and these two forces would negate one another... in turn retarding the timing during cold enrichment periods. I don't see anyway the second port could be used to advance the timing.

I do believe Walt is absolutely correct in that the second port has to remain open. If capped the advance side of the diaphragm wouldn't work... the opposite side of the diaphragm has to be vented to the atmosphere for it to operate. You can clearly see that on the single port distributor has the second hole where the second port would be placed if the application required the dual port distributor and it remains open to the atmosphere. It also seems clear that the dual port versions has one on either side of the diaphragm

2.8Ldistributors.jpg


I'm just trying to capture these part numbers and a bit of how it works to update the Duraspark conversion page because these parts are slowly becoming harder and harder to find.

Thanks in advance for any help.
 

19Walt93

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The car makers struggled to meet the emissions standards in the 70's. The standards would change every 2 years so we'd get new models that ran like crap and the next year would run like a smaller pile of crap. They leaned out the fuel mixture, retarded cam and ignition timing, and dropped compression trying to "clean up" the exhaust. A perfect storm of changes that created V8 Mustang II's with 139 hp that got 12 mpg and 351M F150's that couldn't get 10 mpg in the winter and would barely climb a hill. If I remember right, the vacuum retard came in when the engine was warm, supposedly to more completely burn the fuel mix. Most of the V8 timing sets had 4-6 degrees of retard built in. Cylinder head design suffered because they cast the thermactor passages into the heads, restricting the exhaust ports something awful, I think because it was cheaper than using external thermactor tubes.
If you have a dual advance distributor just ignore the vacuum port, whichever distributor you have- check the centrifugal advance curve. Most engines like the advance to be all in by 2800-3000, my 77 Mustang didn't fully advance until 4500 until I fixed it. A 77 Mustang 302 had 2" exhaust back to the cat, 2" back to the resonator, and 1 3/4" over the axle to the muffler, it probably couldn't turn 4500 rpms.
 

Uncle Gump

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Thank you much Mr. Walt...

I'm going to capture this stuff and get it submitted for an update to the Duraspark conversion page.

Thanks @cyclejohn for the photos.
 

franklin2

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The car makers struggled to meet the emissions standards in the 70's. The standards would change every 2 years so we'd get new models that ran like crap and the next year would run like a smaller pile of crap. They leaned out the fuel mixture, retarded cam and ignition timing, and dropped compression trying to "clean up" the exhaust. A perfect storm of changes that created V8 Mustang II's with 139 hp that got 12 mpg and 351M F150's that couldn't get 10 mpg in the winter and would barely climb a hill. If I remember right, the vacuum retard came in when the engine was warm, supposedly to more completely burn the fuel mix. Most of the V8 timing sets had 4-6 degrees of retard built in. Cylinder head design suffered because they cast the thermactor passages into the heads, restricting the exhaust ports something awful, I think because it was cheaper than using external thermactor tubes.
If you have a dual advance distributor just ignore the vacuum port, whichever distributor you have- check the centrifugal advance curve. Most engines like the advance to be all in by 2800-3000, my 77 Mustang didn't fully advance until 4500 until I fixed it. A 77 Mustang 302 had 2" exhaust back to the cat, 2" back to the resonator, and 1 3/4" over the axle to the muffler, it probably couldn't turn 4500 rpms.
I read in one of the factory manuals that retarding the timing makes you open the carb more to maintain the engine rpm. When the carb is opened more, that is more air introduced into the engine, which gives them the opportunity to tune it leaner like you said.
 

19Walt93

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I read in one of the factory manuals that retarding the timing makes you open the carb more to maintain the engine rpm. When the carb is opened more, that is more air introduced into the engine, which gives them the opportunity to tune it leaner like you said.
Not quite, if the throttle is open more additional fuel is drawn in, too. The lean, retarded tune required more throttle to make any power and killed gas mileage but the EPA measures parts per million out the tailpipe, not parts per mile so net emissions didn't drop much.
My Mustang's 302 has about 350 hp based in quarter mile trap speeds and it's weight and will easily get 20 mph or a little better because it's more efficient. The compression is much higher, the advance curve works, the Holley is actually tuned fairly lean, the 2 1/2" single exhaust flows more than a 2" dual system would, and the roller cam has less parasitic drag that a flat tappet and has a fairly mild profile. Gasoline that wasn't polluted with alcohol would work even better.
Vehicles are designed to meet the federal standards, whether or not it works in the real world. The stop-start feature might save a few drops of gas but the cost of replacing starters and batteries isn't a concern for the EPA. I can get the starter off my 351 Ranger in a few minutes but modern vehicles aren't like that. The best new car I've ever bought was a 99 Taurus with a Duratech V6, to remove that starter the front subframe has to be lowered and the right axle has to be removed. Not a cheap repair. Luckily the original starter was still on it at 196,000 miles when I sold it to one of my techs and he drove it 2 years before trading for a Mustang.
Crash standards are another area where the manufacturers design for the feds. A "Smart" car or a Fiat 500 are cases in point. Air bags don't deploy below a set speed, about 20 mph, if I remember right. If you're driving one slowly through an intersection when someone runs a red light and hits you head on you will find out that the laws of physics out rank the federal regs.
 

tw205

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Did you find a distributor yet? I ran across a guy who has an old pinto with a 2.8 the other day while searching for a starter index plate. Don’t know if it still has the distributor but I could shout at him and find out or send you his contact info.
 

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Did you find a distributor yet? I ran across a guy who has an old pinto with a 2.8 the other day while searching for a starter index plate. Don’t know if it still has the distributor but I could shout at him and find out or send you his contact info.
Go over and get the dist, the short wiring harness from the dist to the ignition box, the ignition box and the carb. I am sure you could sell it on ebay. That small carb they used is hard to find also.
 

19Walt93

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Painless wiring sells connectors and Duraspark harnesses. I like Duraspark but those connectors suck because you have to pull on the wires to separate them.
 

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The painless harness is expensive and not very painless for a person who is a novice. I went ahead and used a HEI module on my duraspark II distributor conversion.
 

cyclejohn

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I do not know whether to post this here, as a tag-a-long, or whether to start a new thread. I have been running the Cardone 30-2671 distributor in lieu of the un-obtanium 30-2691 distributor for a couple of weeks now. To the tune of around 350 miles. I offer this up as my own personal experiences with the set-up and not as speculation.

Should I post it here or start a new thread Admin/Moderator?

John
 

Uncle Gump

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I do not know whether to post this here, as a tag-a-long, or whether to start a new thread. I have been running the Cardone 30-2671 distributor in lieu of the un-obtanium 30-2691 distributor for a couple of weeks now. To the tune of around 350 miles. I offer this up as my own personal experiences with the set-up and not as speculation.

Should I post it here or start a new thread Admin/Moderator?

John
All good John... thanks for the feedback on your results.

I have all the info to update the Tech Article I just need to make it happen.
 

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I do not know whether to post this here, as a tag-a-long, or whether to start a new thread. I have been running the Cardone 30-2671 distributor in lieu of the un-obtanium 30-2691 distributor for a couple of weeks now. To the tune of around 350 miles. I offer this up as my own personal experiences with the set-up and not as speculation.

Should I post it here or start a new thread Admin/Moderator?

John
So that is the dual port vacuum advance version correct? If that's right, how are you hooking it up? The port closest to the dist open and the one sticking out to the ported source of vacuum on the carb?
 

cyclejohn

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So that is the dual port vacuum advance version correct? If that's right, how are you hooking it up? The port closest to the dist open and the one sticking out to the ported source of vacuum on the carb?
Hey Franklin,

The short answer to your question is Yes. The Cardone 30-2671 has 2 ports on it.

I have a vacuum line running from the inline nipple of the vacuum diaphragm to the 'ported' nipple at the top of the Holley carb I am running. I have static (idle) timing set at 11° BTDC. Just as soon as I crack the accel arm on the side of the carb vacuum comes on and timing moves to 27° BTDC. With the accel arm on the carb moved to highway cruising RPMs total timing settles in around 38° BTDC. These #'s are in PARK sitting in the driveway, not out on the road. On the road driving, the 2.8 doesn't ping or do any other unwanted quirky stuff, it just runs real nice.

Hooked to manifold vacuum, with the engine fully heat soaked, it cranked right up and settled into a good idle. Timing immediately went to 27° BTDC. Raising RPMs to cruising speed, the timing settled at 38° total, just like with ported vacuum. I did have to back off the idle screw 1/4 turn to have the same idle speed as using ported vacuum. Using manifold vacuum, I did notice something that I had read about in vacuum sourcing post on the internet, and that was that engine temp dropped 5° degrees at idle while hooked to manifold vacuum.

On cold start, hooked to manifold vacuum, the engine would not catch and run, it just didn't want that much advance when firing off cold. With the engine warmed up, it never missed a beat on re-start.

On cold start, hooked to ported vacuum (which is 0 vacuum until the accel is cracked), one pump of the accelerator pedal, manual choke lever pulled to a point that the choke plate is maybe 1/4" from fully closed, and the engine starts immediately.

I have tried every combination of ported/manifold vacuum sourcing, along with capped/uncapped on the 90° nipple sticking out the top of the vacuum diaphragm and there were no changes in performance (I realize that the word 'performance' is subjective when talking about the 2.8) no matter whether the 90° was capped or uncapped. It just ran great.

The 38° total is my best guess due to the timing marks on the crank pulley topping out at 33°.

38° seems slightly excessive to me and would be easy enough to change if I chose to. We will see.

All of my tinkering has been done without the static timing of 11° BTDC being changed.

John
 

franklin2

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Thanks for that detailed explanation. I too have found ported vacuum works best. I have found if you have a automatic, with manifold vacuum on the distributor the idle is high like you mentioned, so you turn it down to be reasonable, but when you put it in gear, the engine wants to stall. If you move the distributor over to ported vacuum, when you put it in drive the engine rpm is more steady and it doesn't stall. Same with a manual, when you let out on the clutch, it has a tendency to want to stall with manifold vacuum on the distributor.

Sounds like the dual port distributor is a option that will work for people till the supply dries up on them also.
 


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