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Discussion Starter · #1 ·
I got this from mustang spec website. For my stock 289 car and distributor, it says maximum mechanical limit is 14 degrees and maximum vacuum advance is 12.5 degrees. website also says base timing should be 6 degrees BTDC. I’m little confused. 6 plus 14 is 20. So when you are WOT where there is no vacuum, its no where near 32 to 36 Where most people suggest total timing is set. Currently i have 20 degrees advance when canister is connected to manifold port because my base timing is set at 12 and it timing mark reads 32. Is canister adjustable with allen wrench? How do you all set your timing? This is my first Ford and I am customed to tuning Chevy but I thought both are pretty much same when it’s carbureted with distributor.
 

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Those are degrees at the distributor which is 2x at the crank. You disconnect the vacuum when setting full mechanical advance. You will have a designated plate in your distributor that will determine full mechanical advance and springs that determine how quickly it gets there. So you see what your base timing is at 12deg and then you rev your engine until it stops advancing and note that RPM and what the total timing is. If its 36 deg then you know your total mechanical advance is 24deg. My engine didn't hit full advance till about 4k RPM which is way too slow. And you can replace the springs for it to get there by 3k RPM.

Good Article:

Then you would set Vacuum advance.
 

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Discussion Starter · #3 ·
Those are degrees at the distributor which is 2x at the crank. You disconnect the vacuum when setting full mechanical advance. You will have a designated plate in your distributor that will determine full mechanical advance and springs that determine how quickly it gets there. So you see what your base timing is at 12deg and then you rev your engine until it stops advancing and note that RPM and what the total timing is. If its 36 deg then you know your total mechanical advance is 24deg. My engine didn't hit full advance till about 4k RPM which is way too slow. And you can replace the springs for it to get there by 3k RPM.

Good Article:

Then you would set Vacuum advance.
That was great article. So what ever reluctor arm near the stop pin is the total centrifugal advance advance (number x2) I have not checked but it has points in it so I figure it’s most likely factory oem? I’m figuring it has 15L since factory base timing is recommend at 6 btdc (6+15x2). I may have to drop the base timing after test drive for knocking. At current base timing with 93 octane, I am at 42 if indeed all 30 degrees are kicked in.
 

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It is not unusual to see 50* or more of total advance with the vacuum advance adding to the initial+centrifugal advance. But don't worry as the engine will only make maximum vacuum at idle or coasting and never at WOT. So with the engine under load the vacuum advance is 0* and the engine won't be hurt by 36* advance.
 

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Discussion Starter · #6 ·
It is not unusual to see 50* or more of total advance with the vacuum advance adding to the initial+centrifugal advance. But don't worry as the engine will only make maximum vacuum at idle or coasting and never at WOT. So with the engine under load the vacuum advance is 0* and the engine won't be hurt by 36* advance.
just to verify, If my base timing is 12 degrees and when vacuum advance is connected it jumps to 32 degrees at idle. So does this mean my vacuum canister is pushing out 10 degrees of advance at the distributor since it’s 2X at the crank?
 
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