| Timing and altitude [message #308576] |
Tue, 11 October 2016 13:10  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Is there a rule of thumb how much to add per 1000 ft?
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Timing and altitude [message #308579 is a reply to message #308576] |
Tue, 11 October 2016 14:29  |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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JohnL455 wrote on Tue, 11 October 2016 13:10Is there a rule of thumb how much to add per 1000 ft?
John, I lived at some altitude in Colorado, 6000 ft in Colorado Springs (advanced 10 degrees there), and 4800 in Greeley, (advanced about 8 degrees), and I have read on the net, 2 degrees per thousand and one degree per thousand. There comes a point where just advancing until pinging is heard does no longer work, as you will lose power before pinging is heard. Every engine must be different, and of course the gas obtained up there is a couple of points less in octane. I bet Emery or Winterfelt (who lived in Loveland years ago) had the best for the 455 Olds.
I just found a post by Jim K, who says a minimum of 1 1/2 degrees per thousand feet. Should get you in the ballpark.
Best,
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
[Updated on: Tue, 11 October 2016 14:35] Report message to a moderator |
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| Re: Timing and altitude [message #308603 is a reply to message #308579] |
Wed, 12 October 2016 01:59 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Advancing timing really is indirectly affected by altitude.
What I an trying to say is as you reduce the air charge (amount of air) in the cylinders at any altitude you can / should advance the timing. This reduced air charge at altitude can be simulated at sea level by not opening the throttle plates in the carb all the way.
What is suppose to happen is the vacuum advance / retard is suppose to automatically adjust the timing when the air charge is reduced. It seems to me if you are having to change the advance the static timing at altitude for reduce air charge, then the vacuum advance and static timing are incorrect for the situation. Maybe what you ought to be looking at a different vacuum advance and static setting to make the whole system automatic for all levels of air charge and altitudes.
Maybe I'm looking at it wrong.
We are controlling the advance by engine vacuum where it probably should be controlled by the amount of air drawn into the cylinders. I do not know how you do that with a non-computer ignition system.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Timing and altitude [message #308608 is a reply to message #308603] |
Wed, 12 October 2016 08:27 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Ken Burton wrote on Wed, 12 October 2016 02:59Advancing timing really is indirectly affected by altitude.
What I an trying to say is as you reduce the air charge (amount of air) in the cylinders at any altitude you can / should advance the timing. This reduced air charge at altitude can be simulated at sea level by not opening the throttle plates in the carb all the way.
What is suppose to happen is the vacuum advance / retard is suppose to automatically adjust the timing when the air charge is reduced. It seems to me if you are having to change the advance the static timing at altitude for reduce air charge, then the vacuum advance and static timing are incorrect for the situation. Maybe what you ought to be looking at a different vacuum advance and static setting to make the whole system automatic for all levels of air charge and altitudes.
Maybe I'm looking at it wrong.
We are controlling the advance by engine vacuum where it probably should be controlled by the amount of air drawn into the cylinders. I do not know how you do that with a non-computer ignition system.
Ken,
You and most of the rest of the world has fallen (I was there once) into the trap set that was set by carburetor engineer over a century ago. I actually had a semester long class called "Fluids". I still remember seeing all the equations that said that a venturi was a mass flow device (M-dot). Therefore, altitude should be a non-issue. That was nice and I believed it for the next twenty years. Then I had to write reports on work done in a real carburetor flow lab. That was where it was demonstrated to me that the introduction of a throttle plate, a choke plate, an airfilter, a curvy intake manifold and pulsed flow (M-double dot)throw that all right our the window. They become much closer to a volumetric device (V-dot) and they aren't really very good at that. So, they also don't deliver the correct fuel for the different conditions.
Ego, they will not deliver the correct signal to the timing controlled by vacuum devices and with the ambient P less than sea level, they can't even guess what the real MAP (Manifold Absolute Pressure) and as such can't even begin to guess what the cylinder charge pressure (pressure when the intake closes) actually is.
Emery had a good idea years ago (and I cannot locate the picture) where he (before his ECM install) had a pointer on the distributor so he could quickly reset the base timing. A great idea, but an ECM with Knock Sense and timing control is better.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Timing and altitude [message #308613 is a reply to message #308576] |
Wed, 12 October 2016 09:23 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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I went about 2deg clockwise on the cap which should be about 4 deg. I have been developing a slight manifold leak which makes listening for spark knock un fun. Lenzi coppers when we get home. I made marks after re greasing the distrib so easy to home.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Timing and altitude [message #308633 is a reply to message #308576] |
Wed, 12 October 2016 14:13 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Seems to me higher altitude requires more degrees throttle opening and less vac signal to the pot, the inverse of what is desired.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Timing and altitude [message #308801 is a reply to message #308608] |
Sun, 16 October 2016 11:38 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Matt recently posted that I had once made a timing pointer for my distributor.
It is shown here:
http://www.gmcmhphotos.com/photos/timing-marks-for-distributor/p1451.html
I found that this was very accurate for adjusting my timing.
When I lived at Santa Fe at an altitude of 7200 feet I found that I could advance the distributor anywhere and not get pinging.
At high elevations I found that advancing the distributor gave me much more power.
So I would have it at 25 degrees in the mountains but would have to lower it when traveling.
When I got down to, say 3000 feet, I would drop it to about 15 degrees. When I got to California close to sea level I would put it at 8 or 10 to prevent pinging.
This was all before I had a fuel injection controlled distributor with spark control.
I no longer use the original distributor.
Emery Stora
77 Kingsley
Frederick, CO
> On Oct 12, 2016, at 7:27 AM, Matt Colie wrote:
>
> Ken Burton wrote on Wed, 12 October 2016 02:59
>> Advancing timing really is indirectly affected by altitude.
>>
>> What I an trying to say is as you reduce the air charge (amount of air) in the cylinders at any altitude you can / should advance the timing.
>> This reduced air charge at altitude can be simulated at sea level by not opening the throttle plates in the carb all the way.
>>
>> What is suppose to happen is the vacuum advance / retard is suppose to automatically adjust the timing when the air charge is reduced. It seems
>> to me if you are having to change the advance the static timing at altitude for reduce air charge, then the vacuum advance and static timing are
>> incorrect for the situation. Maybe what you ought to be looking at a different vacuum advance and static setting to make the whole system automatic
>> for all levels of air charge and altitudes.
>>
>> Maybe I'm looking at it wrong.
>>
>> We are controlling the advance by engine vacuum where it probably should be controlled by the amount of air drawn into the cylinders. I do not
>> know how you do that with a non-computer ignition system.
>
> Ken,
>
> You and most of the rest of the world has fallen (I was there once) into the trap set that was set by carburetor engineer over a century ago. I
> actually had a semester long class called "Fluids". I still remember seeing all the equations that said that a venturi was a mass flow device
> (M-dot). Therefore, altitude should be a non-issue. That was nice and I believed it for the next twenty years. Then I had to write reports on work
> done in a real carburetor flow lab. That was where it was demonstrated to me that the introduction of a throttle plate, a choke plate, an airfilter,
> a curvy intake manifold and pulsed flow (M-double dot)throw that all right our the window. They become much closer to a volumetric device (V-dot) and
> they aren't really very good at that. So, they also don't deliver the correct fuel for the different conditions.
>
> Ego, they will not deliver the correct signal to the timing controlled by vacuum devices and with the ambient P less than sea level, they can't even
> guess what the real MAP (Manifold Absolute Pressure) and as such can't even begin to guess what the cylinder charge pressure (pressure when the intake
> closes) actually is.
>
> Emery had a good idea years ago (and I cannot locate the picture) where he (before his ECM install) had a pointer on the distributor so he could
> quickly reset the base timing. A great idea, but an ECM with Knock Sense and timing control is better.
>
> Matt
> --
> Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
> '73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
> Now with both true Keyless and remote entry
> SE Michigan - Twixt A2 and Detroit
>
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