Total timing issue - Vintage Mustang Forums
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post #1 of 22 (permalink) Old 04-22-2019, 04:15 PM Thread Starter
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Total timing issue

Hi fellow stangers.
Let me start by explaining my setup.
I have a 289 block from 65 with a 302 crank, and the original 289 heads.
This means that the compression is quite high, which is fine with the fuel we have in Europe.

Im running with a points distributor.

At idle, i measure 25 inch Hg manifold vacuum.

When setting the timing at 6 degrees before TDC I measure a total advance (initial advance + mechanical + vacuum) of 33 degrees before TDC at idle.
When reving up to 2000RPM the total timing advance (6 degrees initial + mechanical advance, no vacuum advance) is 23 degrees before TDC at 2000RPM.
When connecting the vacuum (doesnt matter if its ported or manifold vacuum), the total timing advance (initial of 6, mechanical and vacuum advance) is 51 degrees before TDC at 2000 RPM, which seems like a lot.
It seems like the vacuum advance adds 28 degrees of vacuum advance, this is way to much.
Vacuum is still measured to 25 inch Hg at 2000RPM.

My best guess is that this happens because of the high compression which increases the manifold vacuum.

What i have tried:
Setting the total timing (both initital and vacuum) at 2000 RPM to 36 degrees before TDC, this means that the maximum total advance is 36 degrees before TDC, and the engine seems to be running fine.
Issue:
When measuring the initial timing after this, its aprox 6 degrees AFTER TDC, but when hooking up the vacuum, the timing at idle changes to 17 degrees before TDC.

Did i do it correctly when setting the timing after the total timing advance?
Any recommendations on timing setting here is welcome, it seems like the vacuum is so high that its creating way to much vacuum advance...

BR
Anders
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post #2 of 22 (permalink) Old 04-22-2019, 05:06 PM
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How does the car run? Is there a problem? There might be something wrong with your distributor the way it's hooked up or the timing. I don't think you have too much vacuum though.
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post #3 of 22 (permalink) Old 04-22-2019, 05:14 PM Thread Starter
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The engine seems to be running fine. The distributor is new, but Im not sure about amount the amount of vacuum advance. When the vacuum advance adds 28 degrees of advance it seems like something is wrong. In the workshop manual its stated that the total vacuum advance limit should be around 12 degrees and not 28...
But there isnt any data at 25 inch Hg in the workshop manual, I cant find any data of vacuum higher than 18 inches of Hg.
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post #4 of 22 (permalink) Old 04-22-2019, 09:00 PM
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There is no load to really test the Vacuum advance when in neutral. When I tested mine it also puts a lot of timing, I am not sure what the factory specs should be but you should test going up a hill and decrease vacuum advance if it pings. First set initial and set mechanical advance (both with vacuum disconnected) and finally vacuum advance. Here is a good article on it:

https://www.fordmuscle.com/archives/...ming/index.php

.

1967 Mustang Convertible, 289-4v, C4, Edelbrock Performer Intake, Mild Cam.
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post #5 of 22 (permalink) Old 04-22-2019, 09:15 PM
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Remove your distributor send it to Dan Nolan at the Mustang Barn for proper rebuild and recurve. It will be the best $100 or so you will spend and you will be way ahead of the game. Congrats for sticking with the stock points system. Always use quality Blue Streak or Echlin points and condenser.

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post #6 of 22 (permalink) Old 04-22-2019, 09:40 PM
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Are you using 302 rods or 289 rods?

Bart

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post #7 of 22 (permalink) Old 04-22-2019, 09:48 PM
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Quote:
Originally Posted by Woodchuck View Post
Are you using 302 rods or 289 rods?
I had the same thought.

1965 Mustang
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post #8 of 22 (permalink) Old 04-22-2019, 10:16 PM
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Is your vacuum advance adjustable? If so, dial it down.

Currently working on a 1970 Mach 1 project. See it here: http://forums.vintage-mustang.com/vi...ode-build.html
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post #9 of 22 (permalink) Old 04-22-2019, 10:21 PM Thread Starter
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Shipping the distributor to the US for a rebuild and recurve is not possible as Im located in Europe. In that case I would rather buy a new distributor, recommendations on a distributor is welcome.
Regarding the rods, I dont know, as I havent rebuild the bottom end. My best guess is that its 302 rods, the pistons go all the way to the top of the cylinders, and has a 3 inch stroke.
I have no idea if the vacuum advance is adjustable, its a Cardone distributor, so my best guess is that its not adjustable to low cost of these distributors...
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post #10 of 22 (permalink) Old 04-22-2019, 10:26 PM
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Quote:
Originally Posted by Anders Lange Andersen View Post
the pistons go all the way to the top of the cylinders
Pardon my chuckle. You need to more specific, really...Some of the information is vital to try and get you to a resolution.

Allen

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post #11 of 22 (permalink) Old 04-22-2019, 10:28 PM
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Quote:
Originally Posted by Anders Lange Andersen View Post
Shipping the distributor to the US for a rebuild and recurve is not possible as Im located in Europe. In that case I would rather buy a new distributor, recommendations on a distributor is welcome......"
If you really think there is a fault in the distributor, and If you can't send your distributor to Dan, I'd be contacting him and trying to get him to supply a core. Or buy a good FoMoCo on ebay, have it sent to Dan for testing and re-curving. The reoccurring theme here is to HAVE Dan's hands on your distributor. His work WILL BE superior to ANYONES new distributor.


vacuum in the low 20's is not unusual. I wouldn't worry about 25 inches.

You would hear some pinging if the advance was dangerously high. You say the engine runs fine. I know a dozen guys who would love to say. "my engine runs fine..

So go for a relaxing drive and enjoy your good fortune.


Z
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Last edited by zray; 04-22-2019 at 10:33 PM.
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post #12 of 22 (permalink) Old 04-22-2019, 10:39 PM
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Anyhow, back to the issue at hand.

First, get a new vacuum gauge, unless you're measuring vacuum at an altitude of 3,000 feet BELOW sea level. An idle vacuum, at idle, exceeding 22"hg is almost unheard of.

Next, an initial timing setting of 12*BTDC is typically optimal for a 289 WITHOUT Thermactor. The "later" initial timing settings are used with Thermactor to increase the exhaust gas temperature so that the injection of atmospheric air will ignite any unburned hydrocarbons in the exhaust port/manifold.

Next, let's look at the centrifugal advance curve. The curve for a 289-4V without Thermactor should be something like this:

Distributor rpm (1/2 Crankshaft rpm) Degrees of Distributor Advance
-----475----------------------------------- 2-1/2 to 3-1/2
-----625----------------------------------- 7 to 8
----1200---------------------------------- 10-1/4 to 11-1/2
----1850---------------------------------- 11 to 12-1/4
Maximum spark advance: 14 degrees.

The VACUUM advance curve should look like this:
Degrees of Distributor Advance Inches of Mercury
---------------0 to 1----------------------5
---------------5 to 8----------------------10
-----------6-1/2 to 9-1/2----------------15
Maximum spark advance: 9-1/2 degrees.

In other words, your total timing (initial plus centrifugal) should be around 36 degrees, "all in" by 3,700 engine rpm and pretty much "all in" by 2,400 engine rpm. Vacuum advance is of little consequence to total timing as it decreases as throttle opening increases and at WOT (wide open throttle) will be under 5"hg (unless you have a significant air flow restriction in the intake or exhaust).

A spark advance INCREASE of 19 degrees (the maximum per the specification) upon closed throttle, or at idle using manifold vacuum as a source for the vacuum advance will help the engine run smoother and cooler, albeit with a slightly higher hydrocarbon emission. One key thing to remember is that LEAN fuel mixtures take a LOT longer to burn than rich mixtures. So, say you accelerate to 4,000 rpm then have to suddenly decelerate? You had the throttle mashed pretty well and now you instantly go from moderately rich (power valve open) and low vacuum (< 6.5"hg) to closed throttle, extremely LEAN mixture and high vacuum (>21"hg)? Without the additional spark advance provided by the vacuum advance mechanism, fuel would still be burning in the exhaust manifold and reversion could result in that burning mixture being sucked back in to another cylinder during valve overlap causing a backfire as well as disturbing the natural EGR (exhaust gas recirculation) effect. As a matter of fact, if you've ever watched a race and seen the exhaust flames exiting the tailpipes of a race car when they decelerate for the corner this is exactly what vacuum advance prevents.

Anyhow, hope this info helps and you get your problem worked out.

Oh, and the question about the rods being used... if you used the 302's rods there won't be any increase in static compression ratio as they're 0.016" shorter than 289 rods. Also, depending on the pistons used, you'll lose static compression on compression heights BELOW 1.600" (many replacement pistons are 1.585" CH) and gain static compression at compression heights ABOVE 1.600" (some replacement pistons are 1.605 & 1.608" CH). Also, bear in mind that the valve relief volume on original 289 pistons (pre-'68) was 2cc, so any increase/decrease in valve relief volume will also affect static compression. For example, using a 1.605" CH piston, but one with 7cc of valve relief volume will net a DECREASE in static compression ratio.

:-)
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Bart

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post #13 of 22 (permalink) Old 04-23-2019, 12:09 AM
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Bart, everything you wrote was perfect, but I think the maximum vacuum spark advance in your table should read 19-1/2 degrees instead of 9-1/2, unless I am mistaken!

Thanks for laying down some knowledge for everyone. =)

Would also like to add: A lot of people try tuning their engines with vac advance hooked up. When they see the huge advance numbers, it freaks them out! Don't worry; it's normal.

Because it introduces a dynamic effect into the timing, that's why it's generally best to set mechanical timing according to the numbers, THEN hook up the vac advance, and then tune the carb idle air bleeds/idle speed.

Only after all that's done, if you're still curious, you can shoot your timing light and see what's going on with vac advance. =)
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Last edited by Grimbrand; 04-23-2019 at 12:14 AM.
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post #14 of 22 (permalink) Old 04-23-2019, 07:50 AM
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Quote:
Originally Posted by Anders Lange Andersen View Post
Shipping the distributor to the US for a rebuild and recurve is not possible as Im located in Europe. In that case I would rather buy a new distributor, recommendations on a distributor is welcome.
Regarding the rods, I dont know, as I havent rebuild the bottom end. My best guess is that its 302 rods, the pistons go all the way to the top of the cylinders, and has a 3 inch stroke.
I have no idea if the vacuum advance is adjustable, its a Cardone distributor, so my best guess is that its not adjustable to low cost of these distributors...
I bought a Cardone distributor for my '66 289 and it ran horrible out of the box. Sent it to Dan Nolan for tuning. He found one of the mechanical springs hanging loose and the vacuum advance way too high. A Cardone usually has an allen wrench adjustment in the vacuum advance pod accessible from the vacuum hose port. He tuned it and sent it back. It runs great now.

FYI, I ran a Summit Ready to Run (RTR) distributor while the Cardone was off being tuned. I liked it and found it has a lot of easy adjust-ability to the timing curve and would recommend it. The only reason I didn't leave it in is it was taller than the Cardone and I was going for an OEM look under the hood.

1966 2+2, 289 A code, AOD AT, 3.55 Currie Traction Lock, PS, PDB, AC, Pony deluxe interior & Rally Pac
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post #15 of 22 (permalink) Old 04-23-2019, 09:08 AM
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Quote:
Originally Posted by Grimbrand View Post
"..... but I think the maximum vacuum spark advance in your table should read 19-1/2 degrees instead of 9-1/2, unless I am mistaken!
he is using camshaft / distributor degrees of advance, not crankshaft degrees. So All the numbers he posted are 1/2 of crankshaft degree numbers. When you use a timing light, you are measuring crankshaft degrees.

The shop manual has the specifications listed in distributor degrees because back in day the distributors were taken off the engine and calibrated on a (Sun) distributor machine, so the specifications had to be in distributor degrees

Z.
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Last edited by zray; 04-23-2019 at 09:11 AM.
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