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Old 05-02-2019, 10:14 AM   #1
sphanna
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Default 21,23,28 degrees timing question

There was an excellent post by a well respected engine builder a while back that described the max timing for original and HC engines. 21* for 6;1, 23* for 5.5;1 and never above 28* for stock 4.2 head.

I very much would like to find this post. I. printed it so as to have this info but I have misplaced it. Can any one direct me to this post? My search was unsuccessful. Thank you..
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Old 05-02-2019, 10:54 AM   #2
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Default Re: 21,23,28 degrees timing question

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Originally Posted by sphanna View Post
There was an excellent post by a well respected engine builder a while back that described the max timing for original and HC engines. 21* for 6;1, 23* for 5.5;1 and never above 28* for stock 4.2 head.

I very much would like to find this post. I. printed it so as to have this info but I have misplaced it. Can any one direct me to this post? My search was unsuccessful. Thank you..
This leads to some questions:
1. Where do you set the spark lever to arrive at these settings? It would require fabricating a timing pointer and marking TDC on the pulley, then using a dial-back timing light, and finally marking the timing quadrant so you know where to set the lever.

2. What octane fuel was used to determine these settings? Different octane levels require different timing settings.

3. At what RPM would you go to these "max settings"? Idle? 1,000 RPM? 2,000?
I don't think you can use a 'one size fits all' timing number.
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Old 05-02-2019, 11:11 AM   #3
Jim Brierley
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Default Re: 21,23,28 degrees timing question

I don't have the answer to either of your questions ... but ... generally speaking higher compression does need less spark advance. It also depends on combustion chamber shape and spark plug location. I would think the above stated degrees are a little on the retarded side, especially for stock heads???
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Old 05-02-2019, 11:52 AM   #4
sphanna
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Default Re: 21,23,28 degrees timing question

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Quote:
Originally Posted by 40 Deluxe View Post
This leads to some questions:
1. Where do you set the spark lever to arrive at these settings? It would require fabricating a timing pointer and marking TDC on the pulley, then using a dial-back timing light, and finally marking the timing quadrant so you know where to set the lever.

2. What octane fuel was used to determine these settings? Different octane levels require different timing settings.

3. At what RPM would you go to these "max settings"? Idle? 1,000 RPM? 2,000?
I don't think you can use a 'one size fits all' timing number.
40 Deluxe.

re:Question 1-- I reset the retard enough at TDC so that the desired Max advance with leaver full down, my timing light indicates the max advance on the pulley.

#2. I use Non Alcohol 87 oct. However you do have a valid statement concerning octane vs timing.

#3. All max setting are for 2200 rpm or higher. lower rpm requires less advance..For starting I know where to set lever to attain the 0* All settings verified with timing light.

Alternate way : just set timing at 0* at TDC as usual. Then mark or note the position of the lever when arriving at desired advance.. Again verified by timing light.
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