Good tech info from 'Rush'...A few thoughts...
You ought to know how much total mechanical your distributor gives. On todays' cheap (low octane) gas, 36* (initial plus mechanical) is about as much running advance as (medium hard) acceleration will tolerate. My unit has 20*- 22*...that makes my initial a 14*-16* max.
This is purely a technical point,
ALL distributor advance is 'Mechanical'... There is no electrical or digital component in these obsolte '70's/'80s distributor ignitions.
'Centrifugal' is the technically 'Correct' term for the advance weights/springs,
But common usage is 'Mechanical', another one of those 'Myths' that have persisted through the years, mostly from text books that were simply wrong.
As for centrifugal advance, like I said, it's the minimum SAFE advance.
If your engine will tolerate 36 degrees (Initial + Centrifugal) then by all means run it, and you do what works best for you,
Given you have REASONABLE vacuum signal, and that's not always the case,
I would stick with closer to 24 to 28 degrees Initial + Centrifugal, and make up the difference with Vacuum advance when the engine wasn't loaded so hard for better economy.
24 to 28 is PLENTY for reasonable take off 'Power', and the vacuum will take over and add another 8 to 15 degrees when the engine can easily tolerate it.
After all, I'm NOT drag racing with my Jeep, lots of low speed operation,
Taking off in traffic, pulling hills off road, ect.,
So low end driveability is my main concern...
The other thing that come to mind right away is,
15 to 16 degrees INITIAL... that is at idle, and right off idle...
When does your centrifugal start?
By using smaller/weaker springs, you *COULD* get the centrifugal to START SOONER, and reduce that initial for take off power.
Usually, the centrifugal starts somewhere between 1,200 RPM & 1,500 RPM, which is WAY TOO LATE for good down low power.
On a light weight vehicle with REASONABLE drive train ratios I like to see the centrifugal start about 800 or 900 RPM, just about the same time the carb starts to draw from main jets, and while the fuel enrichment is still active.
I like to see the centrifugal 'All In' by 3,000 RPM at the latest, and on light weight, reasonable drive ratio vehicles, it can be 'All In' by 2,500 with little or no issues...
Like I said, it's a dance between fuel management, Centrifugal, Vacuum and driveability/ final drive ratios and your right foot, so it's a little different for everyone... that right foot can throw a money wrench into about anything I put in print, so I'm hesitant to tell anyone to tune right to the ragged edge!
Depending upon your on-board equipment, you may get better vacuum results from full manifold rather than ported. Many motors can be tuned to either.
Use a timing tape to find what your motor actually does with advance. Use a driving vacuum gauge to assess what the vacuum is doing.
That's what I've said all along...
Spark ported sometimes solves some intermittent transition issues from acceleration to PTC,
Some guys simply don't have spark ported vacuum on factory carbs,
Some guys want full hammering vacuum for this or that... It's personal choice.
I'm inclined to have a SMOOTH transition from idle to no vacuum advance/starting centrifugal advance,
From acceleration/no vacuum to PTC on full vacuum, so I use spark ported vacuum probably more than other tuners I know...
It's personal choice, so I'm not going to argue with the guy that says he 'Likes' manifold over spark ported, it's his choice.
Again, depending on your motor/equipment the limit for cruise should be between 50*-56* @ PTC. This will be your initial, plus mechanical, plus whatever vacuum advance is available.
This is WAY TOO HIGH for any factory distributor I know about!
If you get into the mid 40s it will be a miracle, even more so if your mostly stock AMC engine Jeep tolerates that much at any time!
If that's specific to YOUR engine, then state that.
The way it looks is you are RECOMMENDING people jack in up to 50 to 56 at PTC, which a stock AMC engine WILL NOT TOLERATE.
A FACTORY V-8 distributor, PRE EMISSIONS, will give you about 8 degrees Initial for good starting,
About 18R or 21R for centrifugal, the timing of which will be slow, starting about 1.200 RPM and all 'In' by 3,000 RPM,
The vacuum can will give you about 8 or 10 degrees (emissions cans MUCH less),
And you will wind up with about 39-40 degrees total advance at around 3,000 RPM and around 8-12 in.hg. vacuum signal.
Let's face it, with the average AMC engine, the last one rolled off the assembly line in '90 or '91, so it's tried, and most are at least 30 years old,
That's PLENTY of advance at a reasonable time to keep your engine living for years to come...
*IF*...
You were to build an engine yourself, and you know EXACTLY what you are doing, keeping things that can cause pre-ignition out of the engine, keeping the camshaft reasonable and working with the factory heads/reasonable intake & exhaust,
And you DID NOT stick stupid large tires on 2.73:1 gear sets,
The you could potentially tolerate up to about 50 degrees with few or minor detrimental results.
I'm running 3.31:1 gears on 31" tires, Torque Flight automatic in an '86 GW, FULL REBUILD with headers and improved compression/camshaft, and I'm only cranking 47 degrees at full advance,
Knocking back the ignition by 8 degrees when I tow anything...
It cooks tires, runs 70 MPH on the interstate, gets 17 MPG on highway, and pulls anything I put behind it... (Gets about 12 MPG towing anything heavy)
And mine is pretty standard for everyone I've talked to that's running similar...
Remember that if you run a Holley, richening the mains will not help low speed lean conditions much at all...you will be running on the idle/transition circuit up to about 1200 RPM. If you run around town on big tires use 3rd gear and/or keep RPM's up around 1500 -1800.
By 'Mains', do you mean 'Main Jets'?
If so, that is correct, but I disagree with when the main jets start to work.
Holley is fully adjustable via air bleeds to get the main jets working sooner.
Idle speed, usually 600 to 750 RPM, are idle screw territory exclusively.
Power Valve and Accelrator Pump enrichment will get you from 600 to 1,000 RPM or so where your main jets should start to add to enrichment.
Somewhere around 1,200 RPM you are going to overpower the idle mixture circuit capacity, doesn't matter what Holley you have.
Depending on VOLUME of accelerator pump, and the discharge nozzle size you choose, you will run out of accelerator pump about 1,400 RPM on average.
You can make it much sooner, or much longer, but AVERAGE will be about 1,400 RPM on a hard take off.
You should be FULLY into main jets by then,
And the Power Valve will be working to richen up the fuel mix in a big way,
And will continue to work until you build enough vacuum to close that power valve.
Power Valve should be set to shut down about 2 in.hg to 4 in.hg BELOW PTC point, so it opens up right away if you tip into the throttle a little.
At PTC, you SHOULD have full vacuum advance, the vacuum should have closed the power valve, and you *SHOULD* be running on main jets only,
Your leanest fuel mix being on main jets.
Since there are so many fuel enrichment circuits, accelerator pump, power valve, ect. on a Holley, they are VERY tuneable, and you can run the PTC right up to the point of being a little lean since both accelerator pump and power valve (Properly Adjusted) will add fuel if you need a little more throttle to get up a hill or catch up with traffic during PTC.
When adjusted CORRECTLY, this should all be SEAMLESS AND AUTOMATIC,
Timing drops via vacuum advance, power valve opens via vacuum, and as soon as you tip into the throttle the accelerator pump should give you an instant shot of fuel before vacuum even gets a chance to drop and linkages on vacuum devices to move...
Lastly, no matter what you try...drive it for proof and change one item at a time in between runs. That will be the final determination of your effort.
This is the #1 thing I tell people!
ONE CHANGE AT A TIME!
TAKE VACUUM AND RPM READINGS WHEN YOU HAVE AN 'ISSUE' SO YOU CAN TRACK WHAT'S GOING ON!
Autolite 985, In-cap HEI, 14* initial, 22* distributor, 16* on manifold vacuum, idls set @ 700 RPM. Curve starts @ 850 RPM/Ends @ 2400 RPM. 4.6 stroker, 19.5 MPG on BFG 33's w/ 4.10 and Lock-Right....and yea, I know the Teams thoughts on the HEI 'upgrade'...I use a mellonized MSD gear on a nitrided Comp Cam gear and have machined and spacered it to ride center/center on the cam gear.
YOU HAVE DONE YOUR HOMEWORK!
Sounds like a strong combination!
I was wondering about the 22 degrees of centrifugal advance, now I know!
Never seen a Jeep/Motorcraft with FACTORY 22 degree centrifugal advance head in a Jeep...
Autolite plugs are EASILY Fired by a single coil ignition, so that's a good deal, keep the gap reasonable, 0.035" to 0.045" so you don't overload the internal insulation inside the ignition coil,
Those 'Super Duper' plugs, and CRAZY large gaps to produce excessive voltage have ruined more coils than I can count... All bad ideas...
All in all at least as good as 'Stock' and probably better than stock since you are paying attention to details and doing research,
33" tires on 4.10:1 gears gives you a final drive ratio BETTER than stock vehicle with stock tires and 2.73:1 gears, so that's better than stock.
16° + 22° = 38° before the initial. Most vehicles run fine on 38° total,
But STROKERS take a little more ignition timing...
Not sure I'd get it with INITIAL, but a 52° total I'd keep a CLOSE watch on even in a stroker!
I'm sure you are since everything else about this build sounds so close to dead on what I would have done it's not funny!
Starts at 850, ends at 2,400 is VERY close to what I would have done.
When I'm tuning for power out of the hole, I start VERY early and finish up early.
I take a TON of

when I say I start centrifugal at 850 or 900 instead of the 'Conventional' 1,200 RPM all the 'Text Books' say you are supposed to,
But if you want to get that vehicle moving EARLY, then you MUST get the timing started EARLY.
If the machining/build will tolerate the timing, there IS no such thing as 'Too Early'... It's what the engine will TOLERATE, not what some desk pogue writer thought sounded good when he wrong the text book 45 years ago...
Manifold vacuum on those stiff HEI cans will give you VERY fast vacuum advance drop when you goose the throttle, and that should be keeping you out of trouble. It's the only good thing about HEI vacuum cans, they have a VERY stiff spring in them,
(Two things, they are easy to limit if you get too much total vacuum advance)
I'm taking it you don't do a lot of HEAVY TOWING WITH THIS?

Sounds like a mud bogger to me, It should REALLY clean the tires when you need it to!
Down shift, blip the throttle and throw CAT SIZE MUD CLODS IN ALL DIRECTIONS! :drool: Sounds like a TON OF FUN!
----------------
As for the HEI 'Upgrade', it's a move sideways, just another '70's factory ignition to me. Purely mechanical/electrical engineering standpoint.
When the guys have a 28+ year old ignition in a Jeep, and they start talking about an 'HEI Upgrade', it goes against common sense.
If the gear ON the distributor is 28+ years old,
Or discount 'Sore'

,
It's time for a 'Tune Up' with some quality parts...
AND,
If you are going to buy QUALITY parts, why not upgrade to the better 'Ford' version of same?
It's ZERO cost increase over a comprehensive 'Tune Up', same price as the factory

, but QUALITY factory replacement

,
And that *USUALLY* solves 99.9% of the complaints WITHOUT pulling the distributor and spending $300+ on an HEI Clone and starting the tuning process all over again when the factory unit usually just needs adjusting.
$5 worth of springs, an 1/8" allen wrench and a vacuum gauge usually gets them running just fine...
Just like any other ignition from the 70s, HEI/Clones come with their own set of 'Issues', and you have to spend time/money fixing them,
Gears, install height issues, blown through rotors, good caps/plug wires, ect.
So you are $300 behind in the race, you have to pull/replace the distributor, which is a big deal for some guys (a snap for others),
Since YOU paid attention, got the correct install height, gear mesh, correct gear, ect. you know what I'm talking about here,
Every system has it's 'Quirks' and 'Issues'...
With HEI it's blowing through rotors, with Motorcraft it's leaving the key on and toasting the module...
They are all greasy from the inside out to me, and they all have 'Issues', it's just a matter of what skill level the guy working on it has that is of primary concern to me...
And how deep the pockets are, I don't want to spend someone else's money unnecessarily and overload them on the mechanical/electrical information they should probably need to know...
Cap, Rotor, Wires, Plugs, 'Grounds' are pretty easy, if they still have 'Issues' after that then we go deeper...
It's never the 'Advanced' guys that ask the basic questions...
Like, "I have the factory '1980' distributor cap/wires, should I buy an HEI?"
The answer is always "NO! TUNE IT UP,
GET THAT 34 YEAR OLD

OFF THE DISTRIBUTOR AND WHILE YOU HAVE IT OFF, USE THIS UPGRADE STUFF"
*IF*...
It turns out to be a bad distributor, module AND coil,
Then at least they have reasonable plug wires, and they are only out the cost of cap & rotor when they order the HEI/Clone...
I stress plug wires A LOT!
Once you have a good set of plug wires, and they fit CORRECTLY, it doesn't matter what ignition you put under them.

PLUG WIRES CAN WASTE UP TO 80% OF YOUR SPARK ENERGY ON THE WAY TO THE SPARK PLUGS!
So, it makes sense to have a good set of plug wires...
Just like it make sense to spend $3 to $5 extra on a brass terminal distributor cap, doesn't matter what distributor is under it, this has NOTHING to do with the distributor, it's all about that high voltage spark energy getting WHERE it's supposed to go, WHEN it's supposed to be there!
I got one about a month ago that had spark plugs in it that hadn't been made in 12 years!
When I asked the owner, he said the local 'Shop' (now out of busness) had done a 'Tune Up' on it a 'Couple' of years ago, the shop has been out of business for at least 5 years...
And the spark plugs were 12 years old, the spark plug wires were FACTORY 1980, and the distributor cap was changed, but was the bottom of the line local discount 'Sore' version...
No wonder it had a 'Miss'....
Six plugs, one distributor cap, one rotor, 7 high voltage wires later,
We found a TON of vacuum leaks, fixed those,
Found the choke wasn't pulling off and the high idle was stuck in place, fixed those,
Now it starts in the cold weather, warms up, runs reasonably well for something that was 34 years old and had been running rich with a ton of vacuum leaks for who knows how long...
Now that it starts and RUNS, the guy wants to put 36" tires on it!
On 2.73:1 gears!
On a worn 34 year old STOCK engine!
Just another day in Jeeping!