Z-22/24 distributor vacuum advance

[seattle smitty]

Adjustable vacuum advance canisters can be had for various popular (among rodders) American engines, and many Ford engines came with them.  I don't suppose any such thing exists for the Z-22/24 distributor.  Has any of you found an adjustable vac-advance canister for some other engine that he could adapt to the 8-plug distributor without a whole bunch of trouble?  I expect to do this anyway, but thought I'd ask.  

I rebuilt a '86 Dodge Colt Vista some years ago, and it was a real orphan even then.  The vac-advancer for that distributor was shot, with nothing available.  I figured that parts for small-block Chevys will be available until the sun burns out, so I got an adjustable vac-canister for the HEI and adapted it to the Vista.  Funny-looking, but works fine and had the feature of adjustability (of the internal spring pressure) which I like when making other engine hacks that may affect the desired spark timing curve.

I don't suppose we have anything on the ignition timing curves for the '81 Z-22 engine (in a 720), and of the other NAPS-Z engines, in case they are different, and in case one wanted to experiment with different springs and weights. Usually one is expected to be happy with knowing the factory initial timing setting number, and its hard to find anything beyond that.

Edited July 28, 2018 by seattle smitty

[datzenmike]

How did you quantify the results? The ass dyno is rather unreliable. Besides all this, the vacuum advance is load dependent with more advance at light throttle high vacuum signal and almost none at heavy throttle, low vacuum signal. Springs and weights would be the mechanical advance which is purely RPM dependent and has nothing to do with vacuum.

 

By my count there were 9 different vacuum advance modules on the Z22 depending on California or Federal, 2 or 4wd, long or short wheelbase, manual or automatic.

[seattle smitty]

 A dial-back timing light, Mityvac pump, tach, stopwatch, speedometer, vacuum guage, Innovate air-fuel meter, an ear for ping, eyes to read plugs (iwhen I'm willing to do plug-chops, which is not often!), and a fairly good testing-road up a long grade that doesn't have much traffic at certain times.  I can come up with R.A.D. for what it's worth, though the info I generate with the gear I listed is not as precise as I could wish anyway, so often I just note that it's hot, cold, whatever. I'd a lot rather have a good dyno (and the expertise to use it well) but this is my time-consuming low-buck amateur set-up (and the fact that my procedure is not going to generate papers for the SAE, and will be sniffed at by people who tell us the factory engineers "have it all covered, don't muck around changing things," is not going to stop me from whittling on my stuff).

Mike, since I assumed there were no adjustable advance canisters, the springs and weights are what I was more curious about, as in, were there lots of variations in the curves produced.  Probably so, given all the variants of vacuum canisters you describe. I used to have a suitable spring-tester for distributor work, but haven't seen it in a long time, dang!  In fact I used to have a distributor machine, but sold it long ago when I hadn't used it enough and needed some cash.

Edited July 28, 2018 by seattle smitty

[datzenmike]

By parts numbers there is only one set of governor weights and two different governor springs for the Z22 in the 720. The governor weight is the same as used on the Z20 and the Z24 although both of these distributors use an even different spring. I would say the mechanical advance on the Z22 is limited to no more than two curves.

 

Oh.. the Z22E used in the 200sx and the Z20S in the A10 cars also uses the same weights and another different spring. So 5 different springs for all. It's extremely possible that the L series distributor springs would also fit and give even different curves. Same with the governor weights.

 

As to vacuum advance (part throttle) I would imagine the most advance that when added to the mechanical advance would still be below pinging threshold. This would place the maximum cylinder pressure at about 18-20 degrees ATDC and capture the most energy from the gas and air.

[distributorguy]

The spring tabs are adjustable in most Hitachi distributors, so you don't need to replace the springs in most Datsuns to alter the curve.  You may need to limit timing with a bit of weld.  

 

The vac units... adjustable ones are built in a very stupid manner.  You do two things at once: spring rate changes at the same time as the amount of timing - in the opposite way you would desire.  Cars that need less advance also generally need a higher internal spring rate, not lower.  They're just a gimmick.  There are many ways to limit vac can travel if that's what your intention is?  

Your best bang for the buck is in the mechanical advance curve, so get that dialed in first.  Deal with vacuum when all else is tuned to the end of its life and your vacuum numbers are set in stone.  

 

[seattle smitty]

On 7/28/2018 at 10:05 AM, datzenmike said:

As to vacuum advance (part throttle) I would imagine the most advance that when added to the mechanical advance would still be below pinging threshold. This would place the maximum cylinder pressure at about 18-20 degrees ATDC and capture the most energy from the gas and air.

I'm deleting the EGR on this car, or that's the plan.  Long years ago I acquired a well-used '73 Dodge Swinger 318 that pinged on upgrades.  Initial timing was okay.  I went by the shop of a local engine-builder and he said to disconnect and plug the vac-advance line for the time being, and to check the EGR. These were still years when you could see parts on the engine, and the EGR valve was easy to get at and only held on by a couple of screws.. Turned out to be absolutely packed with carbon.  The thing was riveted together, but I got it apart, dug out the carbon, and tapped it for screws to reassemble.  Told the engine-builder about this and he said, "Bet your engine is slow to warm up."  Yeah . . . ??  "Well, the exhaust crossover passages in your heads and manifold are probably blocked up too, so clean them out."  I did,  hooked everything back up, car ran fine. And yes, THIS one would run fine with the EGR intact and functional, and I wouldn't have to diddle with the timing if I left everything alone. 

I don't have a printer, and I see I'm gonna have to stop at the library to make a paper copy of this thread to refer to.

Edited July 30, 2018 by seattle smitty

[seattle smitty]

On 7/28/2018 at 12:03 PM, distributorguy said:

The spring tabs are adjustable in most Hitachi distributors, so you don't need to replace the springs in most Datsuns to alter the curve.  You may need to limit timing with a bit of weld.  

 

The vac units... adjustable ones are built in a very stupid manner.  You do two things at once: spring rate changes at the same time as the amount of timing - in the opposite way you would desire.  Cars that need less advance also generally need a higher internal spring rate, not lower.  They're just a gimmick.  There are many ways to limit vac can travel if that's what your intention is?  

Your best bang for the buck is in the mechanical advance curve, so get that dialed in first.  Deal with vacuum when all else is tuned to the end of its life and your vacuum numbers are set in stone.  

 

I wish I were handier with this computer stuff, as in posting photos, because I shot a few when I adapted that HEI vac-advancer to the Colt Vista distributor.  One thing I think  the photos would show well enough is the adjustable travel-limiter, external to the distributor body, of which you might approve.
Thanks for the tip on the tabs.

Edited July 30, 2018 by seattle smitty

[distributorguy]

The Corvette guys have one that uses the back screw to hold a notched cam.  The cam can be adjusted to push the rod into the vac can and hold it under higher tension.  Those I do like!!!!  You can do the same thing by welding the hole partially closed as well - from either end of the slot.  

[datzenmike]

EGR can actually reduce pinging by lowering cylinder temperatures. Has no or very little effect on performance as there is little or no vacuum signal at wide open throttle. They can carbon up or stick from exhaust deposits though. There is no EGR at idle so if the valve doesn't close properly it will leak exhaust in. The exhaust is inert and just 'takes up space' in the cylinder. At speed you won't notice anything but idle is carefully set and any loss of fuel and air seriously disrupts it.

 

I had a '69 Charger with 318. When I tore it down the heat passage under the carb in the intake was also totally plugged. Must be a common problem.

[distributorguy]

What does EGR have to do with vacuum advance?

 

Basic timing plot:  Shoot for 14 at idle, + 10 degrees at 2000, + another 10 at 3000.  +2 more above that somewhere closer to 4k.   From there add the vac - whatever it is.    If the vac unit adds too much timing, it'll ping on light throttle tip-in.  You can either mechanically limit the vac at that point or back off the timing a couple degrees.  Mess with the spring tabs to get close and you'll be pretty happy with the plot.  

 

A friend of mine still has a, '86 AWD Colt Vista.  What an interesting piece of equipment...

[datzenmike]

17 minutes ago, distributorguy said:

What does EGR have to do with vacuum advance?

 

 

 

It has everything to do with this post....

 

20 hours ago, seattle smitty said:

I'm deleting the EGR on this car, or that's the plan.  Long years ago I acquired a well-used '73 Dodge Swinger 318 that pinged on upgrades.  Initial timing was okay.  I went by the shop of a local engine-builder and he said to disconnect and plug the vac-advance line for the time being, and to check the EGR. These were still years when you could see parts on the engine, and the EGR valve was easy to get at and only held on by a couple of screws.. Turned out to be absolutely packed with carbon.  The thing was riveted together, but I got it apart, dug out the carbon, and tapped it for screws to reassemble.  Told the engine-builder about this and he said, "Bet your engine is slow to warm up."  Yeah . . . ??  "Well, the exhaust crossover passages in your heads and manifold are probably blocked up too, so clean them out."  I did,  hooked everything back up, car ran fine. And yes, THIS one would run fine with the EGR intact and functional, and I wouldn't have to diddle with the timing if I left everything alone. 

I don't have a printer, and I see I'm gonna have to stop at the library to make a paper copy of this thread to refer to.

 

[distributorguy]

Sorry, not sure how I missed that one.  The carbon mass in the intake does hold heat once the engine warms up, and heat leans out your fuel density.  It doesn't affect timing.  

[datzenmike]

It happens... I miss shit all the time. It doesn't prevent pinging but may reduce it at part throttle. Because the EGR is diluting the cylinder filling of gas and air, to keep up the same speed you have to open the throttle slightly to make up for the loss. This means the engine has less work to do pulling past the farther opened throttle plate. EGR only applies to part throttle. It's off at idle and full throttle.

[seattle smitty]

I take your point, distributor guy.  Unhooking the vac-advancer in that scenario was a quick and dirty way of reducing total timing by some amount (initial timing + mechanical advance + vacuum advance) temporarily.  I could have loosened the hold-down bolt on the distributor and  backed the timing down for the same purpose, but this was a band-aid. Sometimes band-aids are good, like when a guy riding his 2-stroke motocross bike heard it make a thin sound like it was about to seize, and saved it by pulling the choke on, which let him ride slowly back to the pits.

Anyway, my bad for confusing the discussion, starting with one thing and throwing in others in too random a fashion.  At my age, my brain function is getting full of static and mush.

Yes, the older Colt Vistas were interesting, which is putting it charitably for a few aspects of the car.  The earlier Vistas, like my "1987" which was built in late-'86 and still had the smart carburetor as opposed to the real '87s, which had EFI,  were all 2WD or, like mine, 2/4WD with a transfer case, so not AWD like later Vistas.  I bought one that was in nice shape other than a blown engine, liking the fairly sophisticated long-travel suspension and big brakes that Dodge had Mitsubishi put on the 4WD versions.  It's too bad that the Vista is such an orphan, with some parts, such as motor mounts hard to find, because it could be fun for a certain sort of car-guy.  But Vistas were largely bought by and for soccer-moms and other non-mechanical types, so when they got to needing too many trips to the shop they got hauled off to be turned into Chinese re-bar. I like mine, had fun simplifying it and working out the problems endemic to this car,  but I almost never use the transfer case, and would rather have another old 510 wagon as a simpler vehicle that does the same thing for me. But I put so much time and money into overhauling the Vista that couldn't get half what I put into it, and have to keep it.

Edited July 31, 2018 by seattle smitty