[Hotrodjohn71]

Regarding total mechanical advance; (initial plus centrifical), on a stock 1965 326 engine utilizing manifold vacuum.

I have read that 34°-36° is preferred for total mechanical advance.

My HEI distributor has 20° total centrifugal advance. I usually like to set my initial timing in the 8°-10° range, but if I set it at 10°, it will only have a total of 30° total mechanical advance.

And worse yet, if I set initial at 6° which is the stock listing setting, I would only have 26° total mechanical advance.

So right now I have initial timing at 14° giving me 34° total mechanical. It starts OK, but can anyone shed some light on this for me? Thank you.

[steve25]

With today's cut fuel the motor may even want more then 34 degrees to makes its best power!

If at 14 you are creeping into hot cranking issues then it's time to bring back the inatial and get more advance slot travel to extend the mechanical advance.

Since you say your 326 is stock, all of this discussion may be a moot point if you need to replace the timing chain and it's gears!

To me I don't care how the car has been driven over the years, if the chain has over 50K on it it's time !

[george kujanski]

I'll give it a try.....total timing is the sum of initial and mechanical. In your examples, that seems to be what is happening. If you need a higher total timing number you will need to adjust the mechanical advance curve to give you more, while keeping the initial at a good setting. I assume you have the manifold vac disconnected while doing your measurements.

Increasing initial timing to achieve your total has limits, limited by detonation and/or bucking against the starter when starting.

George

[Kenth]

Factory 1965 326 distributor #1111079 starts with 0-4°@800 rpm, 12-16°@1900 rpm and max 22-26°@4600 rpm. Add to that 6° initial.

Vacuum advance #1116243 starts@8-10 in/hg and max 20°@15-17 in/hg.

Looks like your 20° centrifugal HEI and 10° initial will do the job.

HTH

[tom s]

With iron heads and 9.5 CR and Calif really crap fuel,I have found 36 total kind of a sweet spot on numerous dyno pulls with 91 pump gas.From 366 CI to 455 CI with many diff cams.FWIW,Tom

[leeklm]

Pretty common to have a need to increase the travel of the mechanical advance so you are able to achieve something around 25-28 degrees additional advance vs the 20 you are getting now.

Pretty easy to do once the dist is disassembled. Simply remove a little material in the slot/plate with a round file or dremel to allow more travel. Don't go too far, or you will need to back your initial timing way down, or repair the slot by filling in the material you removed with a welder.

I have been using the same HEI on multiple engines, originally had about 36 degrees of mechanical advance, but my aluminum heads only want a total of 30 degrees now. I ended up installing a mechanical stop on the opposite side of the dist plate to limit travel on the low end. I can now run about 8 degrees at idle, 29 total mechanical, + another 10-12 deg from the vacuum advance at cruise speed.

Sent from my SM-G965U using Tapatalk

[steve25]

From 1966 here's what I believe to be the timing curve for the then high comp 389 4bbl 325 hp motor you can use as a reference.

[leeklm]

Per the data Steve just provided, don't forget about vacuum advance. Are you running one, and if so, is it connected to ported vacuum or manifold vacuum? This will make a big difference in your settings at idle.

Sent from my SM-G965U using Tapatalk

[Formulas]

If I was under the hood of your car I would make sure all advance mechanisms are clean and lubricated in working order

Disconnect vacuum advance and remove advance weight springs start engine run at a fast idle to make sure advance weights are in full advance set timing at 32-36 whichever you prefer put springs back on connect vacuum advance lower idle back down then see if there is anything you cant live with

Original specs were a bit conservative plus gasoline formulation is way different and some parts may not be stock

If you set total on low side then decide later you want more total you dont have to do this all over just take note of new initial after this exercise and go from there

[Schurkey]

1. The term "mechanical" advance is a poor word choice. The word you're looking for is "centrifugal" advance. Even the vacuum advance is a mechanical device; unlike the electronic advance used on various computer-controlled distributors. "Total" advance is initial + centrifugal, NOT including the vacuum advance.

2. I don't have too much concern over 14 degrees of initial timing, and I have z-e-r-o concern about the "factory" timing curve, which was deliberately conservative in amount and in the rate of increase with engine speed. Not uncommon to not get full centrifugal advance until 4K rpm or higher. The original engineers threw away power and economy to prevent "ping" when the combustion chambers got carboned-up by Grandma. OTOH, I don't like seeing more than 18-ish degrees of initial timing as excessive initial is often used to crutch poor air/fuel ratio at idle. Excessive initial also leads to starter-motor problems.

3. Those same engineers used too much vacuum advance in many (most) cases, as partial compensation for the slow centrifugal curve. I find that when the centrifugal curve is speeded-up, the vacuum canister needs to be restricted to 10--15 degrees. That's about half the amount that some canisters come with.

4. The "preferred" amount of advance is "whatever the engine/application wants". There's general rules-of-thumb; mid-30s by 3200 rpm is fairly close most of the time...but vehicle weight and gearing, driving style, fuel preference, combustion chamber design (including piston top, and quench distance) all factor into the "optimum" timing curve.

[Murf]

Any chance the timing mark is off?

Murf

[steve25]

Yup, the outer ring of the balancer could have slipped.

He did not post if he checked that,

[lust4speed]

Good news is a stock 1965 326 is going to have the old style hub/damper assembly and timing mark is on the hub and won't move.

Wondering how the HEI was checked and if it was really limited to 20° total advance? HEI's have the habit of tossing in more advance above 4,500 RPM when the weights ride up on the center plate. Determining this is much easier on a distributor machine than with your head stuck down in front of the engine at high RPM.

[Hotrodjohn71]

Thank you fellas.

Yes, I have the older style balancer. It only has one mark which is 6° BTDC which is meant to be aligned with the single pointer on the timing cover.

I used a dial indicator on #1 when I had the head off and scribed a line in the balancer for 0°.

I checked the centrifugal advance with my timing light with the vacuum advance disconnected. I reved the motor until it would not advance further and noted that degree, then subtracted the initial timing and found that the HEI has 20° centrifical.

[67Fbird]

sounds like a solid set..... I had to weld up-file in my advance sounds like you might need some tweeking to get there

[Kenth]

Originally Posted by Hotrodjohn71

Thank you fellas.

Yes, I have the older style balancer. It only has one mark which is 6° BTDC which is meant to be aligned with the single pointer on the timing cover.

I used a dial indicator on #1 when I had the head off and scribed a line in the balancer for 0°.

I checked the centrifugal advance with my timing light with the vacuum advance disconnected. I reved the motor until it would not advance further and noted that degree, then subtracted the initial timing and found that the HEI has 20° centrifical.

1964-65 timing cover with the pointer uses a damper hub with two marks, one TDC and one 6° BTDC.
1966-67 timing cover with a scale uses a hub with one mark, which is TDC.

Sounds like you are using a 1966-67 hub with a 1964-65 timing cover?
Using the TDC mark on this hub against the pointer will give you engine 0° timing advance, not 6°.
May be a part of your timing issues?

FWIW

[Cliff R]

"HEI's have the habit of tossing in more advance above 4,500 RPM when the weights ride up on the center plate."

Correct, but within the "normal" RPM range with the "stock" springs they are usually fine. IF you add aftermarket light springs to one they can and will add timing at high RPM's as this allows the weights to "roll out" on the tips once they have locked into position on the "flats" of the center cam.

The reason most folks don't know this is that they don't rev the engine high enough to set total timing. Every single HEI I've followed on the dyno that did NOT have a positive stop for the advance added timing at high RPM's. For this reason every single one I set up here gets one.

The first pic below illustrates where the factory designed the mechanical advance to stop. The second pic shows adding a positive stop to make sure it can't add any more timing at high RPM's......Cliff

[steve25]

I bet not having / confirming a positive limit at revs above 5k has pounded out a lot of Pontiac Rod bearings and left guys scratching there Heads as to why!

[RocktimusPryme]

I would almost bet you could trade your 20* HEI to someone who has one that lets in more.

As has been mentioned most of the cheap available HEI units work just fine, but allow in too much timing. Both mechanical and vacuum.

[Cliff R]

"I bet not having / confirming a positive limit at revs above 5k has pounded out a lot of Pontiac Rod bearings and left guys scratching there Heads as to why!"

Very possible as at least 75 percent of the HEI's sent in here for work will have very light POS springs from a Mr Gasket or Morroso weight kit in them and or the entire cheezy advance kit with the modified center cam and weights. I've NEVER to date found one of those that worked nearly as well as the factory parts.

What I have found with nearly every one I've worked on is that using light springs and attempts to get all the timing in early allows some of the curve to be in at idle speed. This makes tuning difficult, if not near impossible. One clue this is happening to your engine is that you often see a LOT of drop in RPM's when the transmission is placed in gear instead of little to no change at all. The second clue is the engine not wanting to "settle down" and return quickly to idle speed when you rev it up some. Third clue is idling slower after you restart it as the weights have pulled back in and retarded the timing some after the last shut-down.

Every single offshore HEI I've seen does this, and I'd also mention here that just about every one also had the gear teeth worn and knife edged pretty hard and some only had a few hundred miles of use on them. I would NEVER, under any circumstances install an imported HEI cline if the first place and certainly don't think for a second that the gears they are using are high quality parts.......FWIW........

Below is the pic of a gear I removed from an Olds HEI clone that sells for cheap at most speed shops, Ebay, Amazon, etc. The engine had less than 200 miles on it and the gear was already pretty hard........