The Force Awakens...

ice clear pictures, and yeah I'm rather surprised that you have not graphed out the ignition advance curve
, and engine plenum vacuum at every 500 rpm, level, in detail

I didn’t quite get that granular. I had 18 initial 34 by 2700 rpm and 8 vacuum.

I had checked TDC, but now, I am thinking I’m going to go full on ape on this.
 
This evening I will get a closer eyeball at the ignition. The HEI (coil in cap) is obviously not stock; but it does have a corvette tach drive and gives off a feel of reasonable quality. I'll check the degrees of mechanical and vacuum advance.

I think before I replace the radiator, I am going to fully go through the ignition (and reinstall the thermostat). I think it will still run on the hotter side, but first the ignition needs to be fully sorted out.

My purchase list currently includes:
A CD box.
I do like MSD boxes and have had good experiences with them; they invariably seem to improve things, typically more high rpm stability and a smoother idle and start.

The damper will be replaced too with a full sized one; to control vibration but also to make sure the timing marks are spot on. (Yes, I will verify with a piston stop.)

Plug wires
likely will be replaced.

I would think a carburetor tuning kit would be in order too.

The plugs... should I? If so what should I look for? What would you suggest? Same range as what I have?

I am tempted to replace the distributor with a fully adjustable MSD unit with a corvette tach drive, small cap and MSD blaster 2 coil. But such an MSD distributor and coil add $500. And one thing I have learned about solving issues with cars: don't spend money on the something if it really isn't part of the problem in the first place; you will need the cash to solve the problem.How can I tell if my distributor and coil are good? It looks new: cap, rotor, innards... all of it.
 
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Right-O !

The specs of the distributor are interesting. I did not map how fast mechanical comes out since, for the moment I can’t tune it anyway... but here’s what I have:

Mechanical adds 25 degrees
Vacuum adds 23 degrees

So I set initial at 10 degrees giving me 35 degrees.

I tried both full and ported vacuum on the vacuum advance.

The throttle response is much crisper on ported... but it also gets hotter too. Idling it took five minutes to peak over 210 and get over halfway to the next stripe... presumably 230. I shut it down then.

On ported vacuum, the throttle response was comparatively very poor. However, idle after 10 minutes was still about 210 degrees.

Hmm, 23 degrees of vacuum advance seems a lot.

When it cools off, I’ll inspect the wires, cap, module, etc. to see if I can identify the condition and manufacturer.
 
A good burn in one of the cables. An hour later and the carb is still very hot to touch. I think a phenolic spacer might be in order as well.

I can’t really see any brand or identifying markings on the distributor. It looks new.

D2D1AE1D-AA39-4424-9EC3-37C8A5EC0B1A.jpeg 8988261B-D8FE-4182-A05E-2195D643DC15.jpeg 0F0E09A5-E925-4D69-B5BA-08F0FECFE5F9.jpeg F5599885-93C0-4E24-A3CE-6159A6BD8B8B.jpeg 8AE8FC81-2ABE-4AE2-B4F0-A8A8CE0CF8F8.jpeg
 
that ignition wires generally won,t burn like that unless routed near, or touching ,
a header or exhaust manifold,
while you can,t tell by looking alone,
that distributor, rotor and cap, look to be in good physical condition.
 
Searched high and low... short of pulling the distributor, I have no idea what brand this is. It seems to work fairly well, though.

I have no doubt that plug wire was touching the header.
 
That distributor is new and not GM. That vacuum advance is adjustable.
Use a small allen wrench through the vacuum port nipple to adjust.
Do not go more than 10 turns total. Some of them have a stop, others don't.
If you go too far, the "nut" inside can come completely off, and then it will be trash.
Turn slowly and carefully to feel for the stops.
You are actually adjusting the spring tension on the diaphragm inside, which will control
the RATE of advance.

The distributor works and is nearly new. Leave it alone.
Like you said - don't create a problem where there wasn't one before.
You can always add an MSD box to it later.

That distributor probably is a Skip White (and others on ebay, China) version. I have one myself.
They are actually very good. I have read that what usually fails is the module.
You could (and probably should) remove the module and verify that it is indeed installed with
the white electronic heat transfer grease (not clear dielectric grease).

Add dielectric grease to the module's terminal connections if there isn't any there already.
And occasionally check the centrifugal advance weights for wear. They need to be glass hard.
If they are soft and show wear, then replace them with Moroso's weights.
mor-72300_ml.jpg

https://www.summitracing.com/parts/...MIhpug6cLe2wIVibXACh1wMQ5rEAQYAyABEgJ0d_D_BwE
 
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The distributor works and is nearly new. Leave it alone.
Like you said - don't create a problem where there wasn't one before.
You can always add an MSD box to it later.

Absolutely !!! Thanks !!! I think, I am a little more confident in the ignition now. It does look indeed look like a piece of reasonable quality. I think, in terms of expenses, the MSD box can wait.

You could (and probably should) remove the module and verify that it is indeed installed with
the white electronic heat transfer grease (not clear dielectric grease).

Add dielectric grease to the module's terminal connections if there isn't any there already.
And occasionally check the centrifugal advance weights for wear. They need to be glass hard.
If they are soft and show wear, then replace them with Moroso's weights.

Thanks for the tips and great information on the grease. I think I will pick up an extra module while I am at it.

Agreed, the steel of the weights came across as looking rather soft instead of crisp. That is the only bit that raised an eyebrow... other than the 23 degrees of vacuum advance.

I'll get another look at the plugs this evening and will rewrite my next list to order. I am dropping the distributor and the box. I will replace the plug wires and the damper, for sure. A tuning kit for the carb might be in order.

I hear limiting the vacuum advance to 8 degrees is a good idea. Any thoughts on that?
 
I read a super interesting article here:

http://www.corvette-restoration.com/wp-content/uploads/technical_papers/Vac_Adv_Spec.pdf

According to the author (Lars, a very respected authority) 52 degrees max advance (all is mechanical + initial + vacuum) is the limit of Chevy V8s. I am at 58.

Soooo, from what I can tell, adding manifold vacuum helps the engine run cooler; but on the other hand it kills throttle response.

The next step is to:
- limit the all-in degrees
- lower the limit required for all-in
- give the vacuum advance manifold vacuum

That should contribute to keeping things cool, and give me reasonable throttle response.
 
let us know your changes made and results seen after those changes you made.
 
I hear limiting the vacuum advance to 8 degrees is a good idea. Any thoughts on that?
You have to give the engine what IT wants, not what YOU want to give it.
That said, for now disable the vacuum advance and work with the initial and centrifugal.
Crank up the initial and limit the centrifugal for your combined total advance of about 38 degrees.
When you get that sorted out, then you can add the vacuum advance.
It is a load compensation device that can give you better fuel economy while cruising down the highway with a light load on the engine.
 
Crank up the initial and limit the centrifugal for your combined total advance of about 38 degrees.

By that you mean dial in and up the initial till total reads 38 degrees. If no detonation, then put weaker springs in so that mechanical comes in faster?

When you get that sorted out, then you can add the vacuum advance.
It is a load compensation device that can give you better fuel economy while cruising down the highway with a light load on the engine.

Thanks ! Putting it that way makes it clearer
 
By that you mean dial in and up the initial till total reads 38 degrees. If no detonation, then put weaker springs in so that mechanical comes in faster?

Exactly.
 
Searched high and low... short of pulling the distributor, I have no idea what brand this is. It seems to work fairly well, though.

I have no doubt that plug wire was touching the header.

It’s a Cardone Industries. Although it’s fitted with a module (Mobiletron D1906C) it’s not a performance distributor, this one is an OE replacement.
 
Thanks, Chrome! That helps !!!

Well Gents, I spent a lot of time this weekend tinkering on the ignition; more than I should have due to my own incompetence including forgetting to reconnect the vacuum advance prior to a test drive. The test drive, of course, surprised me with unexpected results. I decided to pull all the plugs... and broke one. :mad: Only after that did I discover my oversight and go for another test drive. This evening I'll pull the plugs again and check the coloration; with the vacuum leak they looked a tick white but clean. No oil or fuel.

Test drive results: With the vacuum advance reconnected (no leaks);
The engine behaves reasonably well overall;
It seems to have significantly more mid range power and throttle response; (quite impressive actually)
Mid throttle is very good. WOT, however, is sluggish.
Cruising at 60 is fairly comfortable (finally!); if loud and annoying at 2800 rpm;
The idle, at 850 rpm, has a vacuum reading with a needle that vibrates rapidly between 20-24 in/Hg; the vibration flattens out at higher RPM. At 2000 rpm, the vibration is mostly gone with the needle stabilizing at 24 in/Hg;
The idle is generally smooth with what sounds like the occasional miss or maybe light popping in the mufflers;
The pops in the muffler get louder on deceleration during the test drive.

Ignition adjustment: Tinkering around, I settled on...
Initial: 14 degrees
Centrifugal: 23 degrees
Mechanical: 37 degrees (begins at 1500 rpm - all in by 2600 rpm)
Vacuum advance: starts at 5 degrees and ends at 14 degrees at 15 in/Hg (I positively limited the advance with a stop)
Total: 51 degrees

Other observations:
That carb seems to get quite hot. I would think phenolic space might be a good idea.
Plug wires need to be replaced; one has a very good burn in it.
The carb has yet to be tuned beyond idle. It is a bone stock Edelbrock 750 CFM. Stock rod, jets, springs, etc.
I haven't driven it enough yet to see if it remains cool at idle. For the moment it does seem to be running cooler.
 
I read a super interesting article here:

http://www.corvette-restoration.com/wp-content/uploads/technical_papers/Vac_Adv_Spec.pdf

According to the author (Lars, a very respected authority) 52 degrees max advance (all is mechanical + initial + vacuum) is the limit of Chevy V8s. I am at 58.

Soooo, from what I can tell, adding manifold vacuum helps the engine run cooler; but on the other hand it kills throttle response.

The next step is to:
- limit the all-in degrees
- lower the limit required for all-in
- give the vacuum advance manifold vacuum

That should contribute to keeping things cool, and give me reasonable throttle response.
58 degrees is too high. The max is what, 51/52? but too high and you get chugging. All this under light load and cruise speed.
Your best torque and hp is at WOT and all in at total advance of 36 degrees
 
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