Can we talk about good timing? - Vintage Mustang Forums
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post #1 of 34 (permalink) Old 03-30-2019, 12:53 AM Thread Starter
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Can we talk about good timing?

So, after fiddling with Pertronix, hard starting, and whatnot, I decided to to go with an HEI distributor. The simplicity and tune-ability of them won my heart. After a little bit of missteps, I've got it running really well right now. (My buddy literally pulled his out of his roadster and gave it to me. I gotta figure out how to repay him.) Anywho, the motor is a 289, edelbrock 1406, mild cam. I gapped the plugs to about .045". I'm getting about 12" of vacuum, which sound pretty good to me. When timing it, I started at 10 degrees, but it really didn't like it. It ran okay, but stumbling at idle, and a dead spot off idle. I increased to 12 degrees, and it's happy a lark. Seems like a lot of timing, so I figured I see what your opinions were.
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post #2 of 34 (permalink) Old 03-30-2019, 02:04 AM
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I don't consider it a lot. If it turns over without struggling I'd call it good. I would check the total, you might need to limit it a touch.

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post #3 of 34 (permalink) Old 03-30-2019, 03:07 AM
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12 was what I ran for years before my car was controlled via ECU. I think 10-12 is fairly normal for a 289/302.

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post #4 of 34 (permalink) Old 03-30-2019, 03:12 AM
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Originally Posted by gregb View Post
I don't consider it a lot. If it turns over without struggling I'd call it good. I would check the total, you might need to limit it a touch.
Yep. It may like 14 degrees even better. But, check the advance curve and see what you have for maximum timing, and at what rpm.

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post #5 of 34 (permalink) Old 03-30-2019, 03:15 AM Thread Starter
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Will do. How much total timing would you consider safe?
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post #6 of 34 (permalink) Old 03-30-2019, 04:15 AM
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jgrote, the 'end' timing is more important than where it starts. Ideally, you'll be somewhere between 28-36 degrees @2800, and all done. 28 = fast burn heads like the GT40P, which does better with the late spark.

Cam timing has a lot to do with this, as does compression ratio. Most 'stock' fords seem to like about 34. Whatever you can get away with on the gas you run, without ping.

If you advance so that your ignition is silky smooth, and it runs like a diesel at WOT, then it's really not going to to any good. Are you running vacuum advance? It's a feature that really helps street driven cars. Drag vehicles only care about whether they can idle (but not idle quality) and what happens at wide-open-throttle. Street cars usually enjoy better idle quality, part throttle, and economy.

Vac advance makes that possible, by advancing the spark when thin mix makes ignition take longer. That happens at idle and cruise. High vacuum conditions in the manifold. When you step on it, vac advance goes away.

So - time your mechanical advance, paying close attention to end timing, but getting your idle timing right too. Adjusting the RPM spread is different for every dizzy.

Once mechanical advance is set, you can hook up your vacuum to manifold vac, and that should smooth your idle out a lot. Then you can adjust idle bleeds and finally, set your idle RPMs on the carb.

Happy motoring.
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post #7 of 34 (permalink) Old 03-30-2019, 06:58 AM
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Just noticed youíre in Denver-ish. Does that mean 5,000 ft-ish of elavation?

If so, that changes things. Air is thinner and thereby actual compression ratios are lower... and your engine will benefit from more (initial and total) timing. Itíll be some trial and error, listening carefully for pinging, detonation or engine run-on.
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post #8 of 34 (permalink) Old 03-30-2019, 10:27 AM
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Run as much initial as possible with out ping. I currently have 19 deg at 2500 ft elevation. I have run as much as 22 with no issues. All in at 35 deg at 2800.
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post #9 of 34 (permalink) Old 03-30-2019, 12:22 PM Thread Starter
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@bbmach, Yes, I'm at about 5500 ft. I'll check total timing later today. It snowed a little last night, so the car is once again tucked in, staying warm in the garage. It was 70 2 days ago! I WANT TO PLAY WITH MY CAR! @Grimbrand, Yes, I do have the vacuum advance hooked up, but to the carb. I was trying to learn more about how vacuum advance works in conjunction with mechanical advance, but still having a hard time wrapping my head around it. I may also need to learn how to adjust the mechanical advance. I know springs adjust when it comes in, but still need to learn how to set the end point.

I just want to stop a second to thank all of you who are taking the time to help me here. Part of the reason I still play with cars is that I love to try things out, learn new skills, and experiment with new ideas. Going into these endeavors with a little knowledge makes it 10 times more fun. I've been playing with old cars since a little before the internet existed, and hanging out at my local parts store was my only way then to get this info.
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post #10 of 34 (permalink) Old 03-30-2019, 01:49 PM
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Its all a compromise, give and take and trial and error. Whatever your combo and climate likes the best.
As you go higher on a good initial * on throttle to get what you want for total * for you you might consider using a ported vacuum for advance. I like it for a nice low RPM at idle but instantly advances once the throttle cracks open.

I think you would be a prime candidate to use O2 sensors.

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post #11 of 34 (permalink) Old 03-30-2019, 03:01 PM
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Think of it this way: The springs and limiters (and direction you have the dizzy clocked) come together to provide Mechanical advance. It only cares about how fast the engine's spinning.

Vac advance always seemed a bit backwards to me, when I was first trying to understand it. "Wait, when the engine's flat-out, it does nothing?"

But basically, that's it. Ignore vac advance, mostly, for setting your timing. Make sure it's disconnected, and that the hose (or vac nipple) is plugged so you have no leak. Vac advance is only an accessory. It does have a profound effect on how smoothly your engine idles, and on your gas mileage, but it will never affect full-throttle operation, and it won't keep your motor from running.

Ported vacuum (the weirdo port on your carb that takes off just above your closed throttle plates) is confusing to a lot of people. It has zero vacuum with the blades closed, but kicks up to full manifold vacuum as soon as they begin to open. A lot of 70s smog engines use this to keep the exhaust hot and make the catalytic converters function better. (Genius! Let's dump more unburnt fuel out the tailpipe in order to reduce emissions!) It's also useful for some cars with a lot of overlap on the cam, because the fluctuations in manifold vacuum can be strong enough to cause surging and stalling from the vac advance while it's just trying to idle.

There are a lot of very knowledgeable people that swear you should always use ported vacuum. It's an ongoing argument that may never be resolved. But to my thinking, it makes no sense to have "zero vacuum" and adjust idle to be perfect running on straight mechanical advance, then transition to a whole bunch of vacuum advance for cruise timing. Such a situation would work fine at full throttle, but not for everyday driving. I believe the best compromise you'll ever get with ported vacuum is an idle that's a bit retarded, and cruise that's probably just a bit over-advanced.

For most cars straight up manifold vacuum works best. If you have it all set right, what works best at idle will also work best at low-throttle cruise, giving you smooth idle, crisp throttle response, and best possible mileage. Under full throttle, the additional advance 'goes away', leaving you with a base mechanical curve that won't ping or detonate, allowing best possible throttle response, safely.
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post #12 of 34 (permalink) Old 03-30-2019, 03:13 PM
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"........ I increased to 12 degrees, and it's happy a lark. Seems like a lot of timing, so I figured I see what your opinions were.
12 degrees BTDC isn't that much. That is the stock specification for the 289 K code (HiPo) engine. Total timing is 40 for the HiPo.

That said, my 289 engines have run best with 16 - 18 degrees BTDC, and total timing limited to 37-38 degrees... A stock distributor has 2 reluctors of different degree ratings, usually the 14L slot (the larger numbered slot) is the factory original setting , switching that for the 10L slot will let you run more initial timing and not have too much total timing.

I don't know if your current distributor has that adjustability.

Z

PS:
At idle, if you can advance the distributor and the rpm goes up, that tells you one thing : the retarded ignition setting is not giving your engine enough time to burn all the gas in the combustion chamber / cylinder. Advancing the timing is giving your engine more time to completely burn the fuel / air mixture, so the rpm goes up because more gas is being combusted (sp ?). Think about it.
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Last edited by zray; 03-30-2019 at 03:18 PM.
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post #13 of 34 (permalink) Old 03-30-2019, 06:14 PM
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Yep, same experience as Zray.

I run 16* initial but mine likes 18* better. I just was trying to limit total advance to 40* so I had to back it off a bit. It's a 289 with a bit of a rowdy cam and it doesn't like to idle at lower than 16.


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post #14 of 34 (permalink) Old 03-30-2019, 08:45 PM
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+1 on on Z and Kelly. I too am running on the 10L reluctor. I added two pieces of shrink tubing to the arm in the slot to mimick the original sleeve, and I get 18 initial and 38 total. I run ported vacuum and tuned my vacuum canister down to account for the extra initial timing. If you run on manifold vacuum with the reluctor on 10L you will probably have way to much initial advance.

Last edited by PA_cob; 03-30-2019 at 08:50 PM.
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post #15 of 34 (permalink) Old 03-30-2019, 08:54 PM Thread Starter
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Thank you so much everyone! I played a little bit with it when I settled on 12, but it did seem to want a little more. I was just afraid to go any further. I'll go to 16 and then check my total and see where I'm at. I assume lighter springs will bring on advance sooner. I may go ahead and order some just to have them. I still need to figure out how to limit the total. I know it's all adjustable on an HEI. I just need to learn how.
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