[glhs#116]

Folks,

This is a particular problem I have had forever on this engine. I'm using all factory mechanical advance stuff with the strongest springs I can find but I still get all my timing in faster than the engine has ever wanted (new heads or old heads, new cam or old cam). Specifically, I get ping between like 1800rpm and 2600rpm way before I get it anywhere else. If I could slow the curve I could run more total and have more early. I could also run more vac advance. Just not sure how to slow it down more. It's not too much total, it comes in too quickly with RPM. 394 centre plate, 139 weights, numbers down (if I remember correctly) which I believe is correct for Pontiac rotation direction.

I think I have a 406 plate as well, also a 345. But the 394 seems my slowest. I am half tempted to take a bit of material off the 139 weights but I hate to butcher good old factory stuff.

Again, I'm not trying to limit the total. I'm trying to get it coming in slower..

Sam

[pastry_chef]

http://www.daytona-sensors.com/tcs-1...ol-system.html

I like things exact.

[Jay S]

Greetings Sam! I see you have the T/A running again. Outstanding! You have really made a lot of things happen to get this far.

I see you have some issues your trying to hash out. I don’t know if any of my ideas will help. But I will try. I went through the other treads you started too. I may get something confused, feel free to correct me. Maybe you can answer some questions:

1. What engine, cam, and compression combos has this distributer been in that you have ran? Has this last combo aggravated it, you indicate it is not totally a new issue?

2. What is your altitude where you are at and normal ambient temp, fuel rating (where your at, i’ll cross reference it.)

3) Which dizzy are you running. It has a pertronix point eliminator in it? What is the initial timing? How much mech advance are you getting and at what rpm does it appear to be all in? Your best guess anyway.

4) What spark plugs/heat range do you have? Maybe a photo of a plug would help to make sure we are not working on a distr problem and not fuel related.

The engine shouldn’t be pinging at all with no load in the mid range for your current combo. That appears to be something you made manageable with the vacuum advance. But that sounds like it is masking another problem.

That 703 cam with the eddy alum heads in a 455 should work at 10:1. It is kind of in the gray area were issues start too occur and would be happier with more cam. But it should be manageable. The issues should be mid range under a load, not at no load or a light load. It sounds like a issue with the dizzy. I am wondering if it is something in the pertronix? Have these issues followed the pertronix around? The advance curve for the parts that are in right now should work. We have done about a dozen Pertronix. Some have been absolutely great, but some had issues also. Do you have a set of points you could try? What year is your pertronix built?



Jay

[glhs#116]

Jay, good to see you. Thanks for all the help!

455HO .030 over
Edelbrock CNC chamber 87cc round port
1971 HO intake
It’s an HEI. The Pertronix is the adjustable vacuum advance unit. Honestly I think it is just a rebrand of the Crane vacuum advance.
Plugs are Autolite 3923 which are listed as compatible with the Edelbrock heads.
Zero altitude. Lots of heat and humidity.

Definitely likes to ping in the midrange light to no load. I can make it go away with more throttle.

So no points. No points replacement. Just plain ol’ HEI

Sam

[Schurkey]

Originally Posted by glhs#116

Definitely likes to ping in the midrange light to no load. I can make it go away with more throttle.

Makes me think the distributor problem is in the carburetor.

You're too lean in the midrange.

[glhs#116]

Originally Posted by Schurkey

Makes me think the distributor problem is in the carburetor.

You're too lean in the midrange.

Try a thinner set of primary rods?

Sam

[Kenth]

Originally Posted by glhs#116

Jay, good to see you. Thanks for all the help!

455HO .030 over
Edelbrock CNC chamber 87cc round port
1971 HO intake
It’s an HEI. The Pertronix is the adjustable vacuum advance unit. Honestly I think it is just a rebrand of the Crane vacuum advance.
Plugs are Autolite 3923 which are listed as compatible with the Edelbrock heads.
Zero altitude. Lots of heat and humidity.

Definitely likes to ping in the midrange light to no load. I can make it go away with more throttle.

So no points. No points replacement. Just plain ol’ HEI

Sam

What is the deal with the Pertronix adjustable vacuum advance?

[glhs#116]

Originally Posted by Kenth

What is the deal with the Pertronix adjustable vacuum advance?

It's what was on the car when I started troubleshooting. It's basically, I think, a rebrand of the Crane unit (PerTronix D9006). Looks the same. Acts the same. 3/32 or whatever allen key to adjust the tension.

Anyway, yesterday when I was troubleshooting I replaced it with the above-mentioned factory advance can (I have like three HEI factory cans from old distributors and this is the stiffest. It is stamped with "20"). So I now have the factory can. It is limited on the back end to 14 degrees with a travel limiter bushing I made. It is now also limited on the front end to 8 degrees by installing the little cam plate thing on the front mounting screw and clicking it three clicks (it takes out 2º per click). I verified this at 12 base, 20 with vac at idle. So it really is adding 8 degrees at present.

Sam

[Jay S]

A couple of the plugs looked like they were burning hot, but not overly so. Just judging that by the white color showing up more down into the ceramic part of the electrode on a couple of them. But really the only thing they tell me is you have done a good job pulling your timing back to keep them running to hot.

Your compression test looked good. I recall you used a little bit undersized dingle ball hone to give 6 some extra clearance. It will probably take a little time to brake that in. Exactly like you mentioned.

There are not necessarily signs that you need a colder plug by reading them. If you just tune a car by ear there will almost never be a sign calling for a colder plug because you are pulling the timing out to manage the hot plugs. The sign is when you put a timing light on the engine, have it tuned by ear with no noticeable pinging, and are way down on your initial timing and the centrifugal timing. When you drop to the next range colder plug the colder heat range let’s you run more advance. Keep dropping the heat range on the plugs until you can get up above 32 full mech advance. Because heat ranges are broad on the hotter plugs you will find were your engine wants it’s full timing in at. If the plug is a bit cold it may want 38. To hot it may want 28. Once you get the heat range right then I would say it is time to start reading plugs and start focusing in on the AFR ratio.

[glhs#116]

Originally Posted by Jay S

A couple of the plugs looked like they were burning hot, but not overly so. Just judging that by the white color showing up more down into the ceramic part of the electrode on a couple of them. But really the only thing they tell me is you have done a good job pulling your timing back to keep them running to hot.

Your compression test looked good. I recall you used a little bit undersized dingle ball hone to give 6 some extra clearance. It will probably take a little time to brake that in. Exactly like you mentioned.

There are not necessarily signs that you need a colder plug by reading them. If you just tune a car by ear there will almost never be a sign calling for a colder plug because you are pulling the timing out to manage the hot plugs. The sign is when you put a timing light on the engine, have it tuned by ear with no noticeable pinging, and are way down on your initial timing and the centrifugal timing. When you drop to the next range colder plug the colder heat range let’s you run more advance. Keep dropping the heat range on the plugs until you can get up above 32 full mech advance. Because heat ranges are broad on the hotter plugs you will find were your engine wants it’s full timing in at. If the plug is a bit cold it may want 38. To hot it may want 28. Once you get the heat range right then I would say it is time to start reading plugs and start focusing in on the AFR ratio.

So.. Interesting. I ordered BKR7E plugs and BKR8EIX (these are Iridium -- couldn't find copper plugs for the cooler ranges). Since my ignition is so retarded right now I went straight to the "8" plugs when I got them. I've been sick so this morning was my first chance to try them. I fully expected that these would be WAY too cold and I would have fouling issues. But.. Hmm.. Maybe I might even try "9"s if I can order some.

I haven't had much time at all to dial these in. Here's my notes from this morning:

1. Set idle advance from 3 without vac (25 with, can adding 22) to 12 without vac (34 with, can still adding 22). Happy idle but a little pingy if I rev it no load
2. One turn tighter (back off allen screw) on the vac can to where it adds 18 at idle in gear. Clean no load rev. Some slight ping on part throttle on test drive
3. One more turn out on vac can to where it adds 16 at idle in gear. Clean for entire drive to work. Some ping when I tried full throttle in 2nd and 3rd in midrange RPMs.

For this I will back off base timing to 10. But I'm sure I shouldn't have to if the plug isn't too hot. I will check it at home later if I get time to pull out the plugs.

Seems weird, right? Clearly the "6" plugs were too hot because this is a MUCH better result than before. Engine, of course, running cooler with the better advance curve. Car drives better cleaner and stronger. But a lot of other people on here saying that "6" is good for their combo and "7" is for turbo/supercharger. Well, I'm at "8" and it looks like I might be better off with "9". Could it be quench distance? My pistons are pretty much at zero deck and I'm with the .039" 1016 head gaskets. Of course it is hot and humid like hell here but I had a very normal advance curve on the old 197 heads and 068 cam in this climate..

Sam

[Half-Inch Stud]

either jet up or science -out the ilde bleeds. Put a
q-JET on and see if the problem goes away.

[Jay S]

Ok, HEI, and a stock gm module with a qjet.


So you are near sea level, with heat and humidity? Normally the 3923 should be fine, it is already a pretty cold plug. Might try a colder plug though. If anything it would give you some hints what the engine is wanting, The vacuum advance isn’t doing you any good if it makes it ping with no load, your better off not running it until you get farther in your tuning..Maybe a 3932 autolight or a 3922 plug would be worth trying. If it is doing this with partial or no load it probably won’t show up reading the plugs. I think I would start there before I spent a bunch of time recurving the distributer.

[Cliff R]

Are you working with a GM HEI or aftermarket HEI?

[glhs#116]

Originally Posted by Cliff R

Are you working with a GM HEI or aftermarket HEI?

GM. It’s in good shape. I try to avoid aftermarket parts where possible.

Sam

[Will]

Is this happening with or without vac advance?

[Schurkey]

^^^ really good question.

"I" would like to see a chart of advance vs. RPM, and vacuum advance vs. vacuum level. And then a description of vacuum produced by the engine during the detonation.

[glhs#116]

So.. This morning I found the little limiter cam plate and I stuck it in with the factory 14 degree can I put in yesterday. I did three clicks and confirmed that I am now at the following:
base 12
with vac 20
vac adding 8

This setup is now mostly ping free but has remaining ping in the aformentioned midrange (like 1800-2800rpm) on light throttle. I actually might have heard a little rattle around 3000rpm at full throttle so I'm thinking my next step is going to be dropping base to 10 for:
base 10
with vac 18

I will try this later today and see what it is like on the drive home.

My notes on my current centrifugal curve (394 centre plate numbers down, 139 weights, stiff OEM springs) is (from my notes):
+8 at 1500
+12 at 2000
+13 at 2500
+14 at 3000

I haven't been able to get a slower centrifugal advance curve than that.

Sam

[Kenth]

Midrange light throttle ping is a classic symptom of a too light spring in the vacuum advance.
Using an aftermarket adjustable vacuum advance only gives new gray hairs and a new vocabulary, i never got one working properly.
I would try to find a 20° Standard VC389 replacement vacuum advance unit, connect it to a ported vacuum source and forget it.
However, if centrifugal comes in full at 3000 rpms or earlier i would shorten the advance slot on the vacuum advance bracket by a quarter of the distance to have 15°.
You may have an original vacuum advance with 25° advance, the amount is stamped on the bracket along with the three last digits of the part #. For this, shorten the advance slot one fifth of the distance for 20° or 2 fifth´s for 15° advance.
The OEM vacuum advance or the VC389 will drop off advance quicker (properly) at light throttle reducing or eliminate ping.
Also, try to find some springs that holds back the max centrifugal advance to at least 3800 rpm´s. Original springs are hard to find, but are the best, should never be replaced. IMHO.

[glhs#116]

Originally Posted by Kenth

Midrange light throttle ping is a classic symptom of a too light spring in the vacuum advance.
Using an aftermarket adjustable vacuum advance only gives new gray hairs and a new vocabulary, i never got one working properly.
I would try to find a 20° Standard VC389 replacement vacuum advance unit, connect it to a ported vacuum source and forget it.
However, if centrifugal comes in full at 3000 rpms or earlier i would shorten the advance slot on the vacuum advance bracket by a quarter of the distance to have 15°.
You may have an original vacuum advance with 25° advance, the amount is stamped on the bracket along with the three last digits of the part #. For this, shorten the advance slot one fifth of the distance for 20° or 2 fifth´s for 15° advance.
The OEM vacuum advance or the VC389 will drop off advance quicker (properly) at light throttle reducing or eliminate ping.
Also, try to find some springs that holds back the max centrifugal advance to at least 3800 rpm´s. Original springs are hard to find, but are the best, should never be replaced. IMHO.

It's a factory 20 degree can limited at the "back" of the slot already to 14 degrees and now limited at the "front" of the slot with the cam plate to 8 degrees. Limiting at the "front" like that should also raise the vacuum required to start advance.

I have strong original springs. Sounds like I need stronger ones but no idea where to get them..

Sam

[Schurkey]

Originally Posted by glhs#116

So.. This morning I found the little limiter cam plate and I stuck it in with the factory 14 degree can I put in yesterday. I did three clicks and confirmed that I am now at the following:
base 12
with vac 20
vac adding 8

So at idle, you have 8 degrees of vacuum advance...which means manifold (not ported) vacuum.

How high above curb idle do you have to rev the engine to get ONE degree of centrifugal advance? In other words, are you sure there's no centrifugal advance at idle?

Originally Posted by glhs#116

This setup is now mostly ping free but has remaining ping in the aformentioned midrange (like 1800-2800rpm) on light throttle. I actually might have heard a little rattle around 3000rpm at full throttle so I'm thinking my next step is going to be dropping base to 10 for:
base 10
with vac 18

I will try this later today and see what it is like on the drive home.

My notes on my current centrifugal curve (394 centre plate numbers down, 139 weights, stiff OEM springs) is (from my notes):
+8 at 1500
+12 at 2000
+13 at 2500
+14 at 3000

1. Is the advance DONE at 3000 rpm, or does it continue to advance as RPM increases?

2. Are we talking about crankshaft degrees, or distributor degrees? With 12 degrees initial read off the crank damper, and +14 crank degrees from the centrifugal advance, your total timing at 3K is 26 degrees. Likely not enough. With 12 degrees initial, plus 14 distributor degrees of centrifugal advance, you have total timing of 40 degrees at 3K--very likely too much. EITHER WAY you need to straighten out your centrifugal advance.

3. The vacuum can is limited on both the "front" and the "back", but you've never said how much vacuum it takes to activate, and how much vacuum it takes to fully advance. Similarly, you haven't said how much vacuum the engine is developing when you hear the pinging.

4. I still have a hunch that you need more fuel. But what do I know? I'm ten thousand miles away.

Originally Posted by glhs#116

I haven't been able to get a slower centrifugal advance curve than that.

Do you have the extra-heavy weights? Perhaps lighter weights are in order.