#21  
Old 10-07-2019, 10:55 AM
Formula jg Formula jg is offline
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David, to clarify current timing settings as follows:
Initial 10*
Mech 22*
Total 32* all in @ 2000rpm
Load Compensator with home made set stop for 9* @ 8"Hg

Anything above 34* total this engine starts to pre-detonate even more so with such a fast curve being all in by 2000 rpm.

In my post #17 there is a pic of half the springs I have and none of them are able to slow down the curve with exception to the bottom left but unfortunately the pair I have will not return the weights completely. It appears the after market springs won't slow this curve I need some stiffer ones like those that came originally on these HEI's. Been searching online but can only find aftermarket spring sets, going to a friend's shop this week and hopefully find some there.
  #22  
Old 10-07-2019, 12:54 PM
David Ray David Ray is offline
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Pickup coil has single windings wire to stranded wire interface problems, and, second issue might be the actual strands are broken at the terminals in the plastic connector block that interacts into the end of the HEI module. Since the wires have to actually bend as the vacuum advance operates, it is possible that every strand of the wire at the terminal is broken, and only making intermittent contact in certain positions. If you can, set the ohm meter up to read the resistance, and wiggle the wires at the connector block. If the strands are broken, the reading will go bonkers as you wiggle the wires.

For the high tension leads, red to white, ACCEL, 500 ohms is good, that is within their guidelines. From red to coil wire terminal, the 8,950 also sounds like what they used to have, BUT, the coil is still dead cold, not at operating temperature. to properly test the coil, it needs to be hot, at ops temps. To do that, find a good auto parts store that has an off vehicle electrical tester that runs coils on it, load it up, and let it run, get it to temperature, and see if it is good.

That ACCEL coil is one that was made at Andover Industries, Andover, Indiana, at that time, THE best coil producer in America. It is very likely that coil is still very, very nice in condition.

Reading your timing specs, I assume the IDLE timng is 10 INITIAL, plus 9 vacuum advance, sourced on full manifold vacuum, and NOT ported vacuum. Is this correct?

For the large HEI, points distributor springs interchange, and there are tons of them all over the place. Example: ZZ springs LOOK like they are very light tension when they are just sitting on the bench, but as they are mouned to the pins, they stretch a great deal, and become very high tension. This radically slows down the mechanical curve, to start the ZZ curve at 1,300 or so RPM's, and limits it to 5,500 RPM's. Reason: The ZZ has the vacuum advance sourced on ported vacuum, which causes it to come in upon acceleration, not the right way to do it, but that is the way the EPA had GMPP run the distributors, so the engines can get certified to sell. Vacuum advance is NOT supposed to be a second acceleration advance curve, and GMPP had to slow the mechanical advance curve extremely down to dead slow, to allow the vac adv to work on ported, which is the wrong way to do it.

So, in the case of the ZZ, the mechanical advance was slowed down to allow the ported vacuum advance to operate, but it really doesn't work well that way. Limiting the vacuum advance to a reasonable number of degrees, running it on full manifold vacuum, and speeding the mechanical curve up with softer springs, starting at 850/900 RPM's, limiting to 3,000/3,100 RPM's.....does.

Last edited by David Ray; 10-07-2019 at 01:07 PM.
  #23  
Old 10-07-2019, 06:46 PM
Formula jg Formula jg is offline
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Of the 5 pickup coils I have 3 are new and 2 used. all tested with similar ohms when at rest and fluctuating ohms when moving the wires. I can't keep buying or returning these things until I find a unicorn that has a steady reading, just not practical so I will work with what I have for now.

I think I'm going to put the Accel coil back in, it definitely fires up the engine with much more bang than the brand new ACDelco coil I just put in there.

The timing specs you noted in your last post are correct.
  #24  
Old 10-07-2019, 07:50 PM
David Ray David Ray is offline
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The majority of the wire failures on large HEI magnetic pickups are fraying of, then intermittent connection to the two terminals inside the plastic connector that fits the two wires onto the end of the HEI module. At that wire to terminal junction is where the most movement occurs between the wires and module as the pickup rotates.

As I have written elsewhere, there are two ways to obtain a new pickup coil. As a simple coil, which is not the best way, because when the pickup is disassembled to replace the coil, there is no real easy way to center the outer reluctor so it doesn't hit the inner reluctor, unless you build a centering tool, and you need a lathe to build one that is accurate. Second, the easiest way, purchase the entire fully assembled, and factory centered pickup assembly, still not radically expensive. .
  #25  
Old 10-08-2019, 04:39 AM
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Dave, "Reason: The ZZ has the vacuum advance sourced on ported vacuum, which causes it to come in upon acceleration, not the right way to do it, but that is the way the EPA had GMPP run the distributors, so the engines can get certified to sell. Vacuum advance is NOT supposed to be a second acceleration advance curve, and GMPP had to slow the mechanical advance curve extremely down to dead slow, to allow the vac adv to work on ported, which is the wrong way to do it."


I have found past off-idle there is NO difference how the load compensator works.
It will always reduce the amount of ignition timing at heavy acceleration, ported or full manifold source used.
Please explain how a vacuum operated load compensator would ADD timing at acceleration?
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  #26  
Old 10-08-2019, 11:45 AM
David Ray David Ray is offline
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"Please explain how a vacuum operated load compensator would ADD timing at acceleration? "

Welllllll, as we all know, full manifold vacuum REDUCES upon engine acceleration, because engine vacuum reduces as throttle position is increased, during engine acceleration. So, there would be no additional timing, no second acceleration curve as this occurs.

PORTED vacuum is moot at low to no load, and high engine vacuum levels, such as no to light load cruise, and when the engine is accelerated, vacuum is created at the ported port, bringing into operation, the 'load compensator', forcing it to work completely opposite of how it should, adding vacuum advance degrees upon engine acceleration, CREATING A SECOND ACCELERATION ADVANCE CURVE ADDED TO THE MECHANICAL CURVE, MAKING TWO DISTINCT ACCELERATION CURVES.

That's how.

Last edited by David Ray; 10-08-2019 at 12:33 PM.
  #27  
Old 10-09-2019, 02:35 PM
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"Welllllll, as we all know, full manifold vacuum REDUCES upon engine acceleration, because engine vacuum reduces as throttle position is increased, during engine acceleration. So, there would be no additional timing, no second acceleration curve as this occurs."

Since manifold vacuum is reduced at the same rate, ported or full manifold source to the load compensator the result would be, and what i have found, the same, reduced timing advance at acceleration.
Test driving with a vacuum-meter teed to the load compensator hose will show no "second acceleration curve".
The needle may hick-up when the throttle blade passes the ported source slot in the bore creeping away slowly with the car, but i would not call that hick-up "second acceleration curve".
Maybe this can be accomplished with some sort of delay valve for the load compensator?
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  #28  
Old 10-09-2019, 03:20 PM
David Ray David Ray is offline
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WRONG.

Since ported vacuum is taken further up the throttle bore, well within the smallest diameter of the venturi, vacuum is created there, to pull a vacuum advance diaphragm into adding timing during acceleration, or, make a second acceleration timing curve..

The vacuum signal at the base of the carb at WOT is extremely low, to completely NIL, so, no vacuum pull, no vacuum advance timing on full manifold vacuum sourcing at full throttle, NO secondary acceleration timing curve..

VAST difference with vacuum levels between full manifold and WOT ported sourcing.

Try driving around with TWO vacuum gauges connected, one to each type port, as I have, many, many times.
  #29  
Old 10-09-2019, 04:57 PM
Formula jg Formula jg is offline
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I’m not qualified to debate this either way and I’m not picking sides here but can confirm after countless testing of both ported and direct manifold setups my combo idles and runs better and cooler on a direct manifold setup to the load compensator.

On another note I scored a couple of advance springs today, they feel stiff enough to slow down this curve but won’t know for sure until the weekend.

Also, someone suggested I check fuel pressure when stabbing the throttle under load as the mech. fuel pump may be acting up and causing the stutter/stumble and excessive lean spike condition that we have been chasing, another test for the weekend.
  #30  
Old 10-09-2019, 04:57 PM
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Ok, are you suggesting that venturi vacuum is activating the load compensator at the ported vacuum source at acceleration with low intake manifold vacuum?
That sounds odd since the ported source is below the throttle blade exposed to intake manifold vacuum, or lack of vacuum, at acceleration.
My observations differs from yours, i have found vacuum drops at the same rate at acceleration, ported or full manifold source..
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  #31  
Old 10-09-2019, 09:48 PM
David Ray David Ray is offline
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Ported vacuum is NEVER sourced below the throttle blades, it is ALWAYS sourced at the smallest diameter of the bore venturii, that is why, as the air flow is high there when the throttle is full open, vacuum is significantly higher there, than at or below the throttle plates.

Connect two vacuum gauges and go drive the engine around, full throttle it, idle it, and then, cruise, mild acceleration, all facets of operation. You will get the correct picture then.
  #32  
Old 10-10-2019, 04:44 PM
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Quote:
Originally Posted by David Ray View Post
Ported vacuum is NEVER sourced below the throttle blades, it is ALWAYS sourced at the smallest diameter of the bore venturii, that is why, as the air flow is high there when the throttle is full open, vacuum is significantly higher there, than at or below the throttle plates.

Connect two vacuum gauges and go drive the engine around, full throttle it, idle it, and then, cruise, mild acceleration, all facets of operation. You will get the correct picture then.
Like i wrote, ported vacuum IS sourced from below the throttle blade, AT ACCELERATION.
You obviously haven´t looked into the bores of a carburetor with a ported source for the vacuum advance (load compensator, as you state it sits in the smallest diameter of the venturi.
NO PORTED SOURCE FOR ANY VACUUM ADVANCE IN ANY CARBURETOR SITS IN THE SMALLEST DIAMETER OF THE VENTURI, PERIOD.

The only carbs using venturi vacuum is HOLLEY´s with vacuum operated secondary valves.
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  #33  
Old 10-10-2019, 07:20 PM
David Ray David Ray is offline
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Hilarious, very entertaining.

So, NO other carb creates ported vacuum above the throttle plates. That is just plain false.

It seems in your world, other carb manufacturers simply cannot drill any vacuum passages other than straight into the side of the base plate, no passages upwards and sideways into the top of the venturii, as I have seen for decades.

And, well, I do have to confess, I do have extensive carburetor experience, as when I worked for Duntov at Skunk Works, I did engine design development, helped develop the coil in cap HEI, AND, worked extensively on carburetor development.

I also worked at Holley for a few years, I band sawed Dominator's in half for Pro-Stock racing, creating "Split-Dual" carbs for drag racing, and working directly for the racers.

By what you say as to ported vacuum production in non-Holley carbs, the same could be said from you, that there cannot be any oiling of an engine past the point of crankshaft feed galleries, because there are never any oiling passages drilled in engine blocks upwards to deliver oil pressure and oil above the crank center lines, and no water above the water pump insanity as well, nor can you drink any liquid from a cup that is half full even with a straw and suction applied, nor blow bubbles from that straw downward into the liquid, either. I am sure you will use those erroneous examples to prove your incorrect point as well, next.

PLEASE, "stop all this no ported vacuum above the wide open throttle plates" BS, we know better. Give it a rest.
  #34  
Old 10-11-2019, 04:28 AM
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Dave,

It looks like, unintentionally, you have introduced confusion into the discussion with your statement in post #31, 'smallest diameter of the bore venturi'.

The bore [ throttle bore ] is different to the venturi, & is located below the venturi on downdraft carbs. The diameter of both is also different, creating different pressures.

I think you also misunderstood or misread what Kenth said about the PVA port being below the t/blades; he said this is the case during acceleration, when the t/blades are opened for power. At idle, the PVA port is above the t/blades & I think we are all in agreement about that.
  #35  
Old 10-11-2019, 09:29 AM
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Quote:
Originally Posted by David Ray View Post
WRONG.

Since ported vacuum is taken further up the throttle bore, well within the smallest diameter of the venturi, vacuum is created there, to pull a vacuum advance diaphragm into adding timing during acceleration, or, make a second acceleration timing curve..

The vacuum signal at the base of the carb at WOT is extremely low, to completely NIL, so, no vacuum pull, no vacuum advance timing on full manifold vacuum sourcing at full throttle, NO secondary acceleration timing curve..

VAST difference with vacuum levels between full manifold and WOT ported sourcing.

Try driving around with TWO vacuum gauges connected, one to each type port, as I have, many, many times.
I can assure you i know the difference between the ported or the full manifold source for the ignition vacuum advance, and why either is used.

Wouldn´t it be easier for you to just give an example on any carb or engine that uses a ported source to add a second advance curve from the ignition vacuum advance, instead of twisting and turning my words against me and make up fantasy statements?

Thanks.
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