Timing Vs Rotor phasing

ksurfer2

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What relationship exists between timing on the crank and phasing on an adjustable rotor? Here is my example, I am running 35* of timing (locked) on my 512. I have an adjustable rotor to assist with proper phasing. When the rotor is lined up with #1, it is moved approximately 7-8* off center. I have confirmed TDC on the crank.
 

matthon

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I recently went through this, not an expert, just watched multiple videos, searched forums and the interweb.
I found most videos contradict themselves in the same video, as well as other videos, and leave out steps.

My ready to run dizzy was set at 20* btdc.
I set my crank there, then set my pickup at one of the pickup spokes, and also set my adjustable rotor at the #1 cylinder.
The adjustable rotor wasn't far off from it's center mark.
Cut a hole in an old cap, marked a line on the rotor, started engine.
Phasing was setting the rotor where it sweeps across the #1 post during a specific rpm range, in my case idle to 4k, iirc, according to the efi specs.
The rotor is now always as close to the post as possible at all rpms, and the pickup is lined up.
I found mine runs best with the rotor just past the post at idle, and it sweeps back to on it at 4k, and just before any higher.
 

451Mopar

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What relationship exists between timing on the crank and phasing on an adjustable rotor? Here is my example, I am running 35* of timing (locked) on my 512. I have an adjustable rotor to assist with proper phasing. When the rotor is lined up with #1, it is moved approximately 7-8* off center. I have confirmed TDC on the crank.
If your dist is locked out, just set crank to the 35-degree BTDC timing, and rotate the rotor to be in line with the cap terminal.
 

ksurfer2

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If your dist is locked out, just set crank to the 35-degree BTDC timing, and rotate the rotor to be in line with the cap terminal.
That is the way I set it up. I was just wondering if there was a relationship between timing at the crank (35*) and how far off center the rotor moves to line it up with the terminal on the cap (7*).
 

Nxcoupe

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I was under the impression that rotor phasing was for efi vehicles that use the distributor for cam/crank positioning? If you use a timing light to set your timing, initial and total, the rotor is positioned where it needs to be. With efi, if you put the plug wires on incorrectly oriented on the cap, it will inject fuel into the wrong cylinder while still appearing to be properly timed.
Maybe I'm missing something it seems to be picking flyshit out of pepper? Always willing to learn, so if someone can fill me in on the differences and correct my thinking, I'd appreciate it.
 

ksurfer2

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It is my understanding that as timing is advanced, it moves the rotor further away from the terminal it is firing, in some cases, this may cause a miss fire as the spark will jump to the wrong terminal. Adjusting the phasing, lines the rotor up with the proper terminal.
 

Nxcoupe

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It is my understanding that as timing is advanced, it moves the rotor further away from the terminal it is firing, in some cases, this may cause a miss fire as the spark will jump to the wrong terminal. Adjusting the phasing, lines the rotor up with the proper terminal.
Which occurs by retarding timing a bit? Unless you are referring to rotor placement vs the trigger of reluctor aligning or points opening causing the spark to occur? If that's the case, then it makes sense to me, however, that will also affect the crank degree at which the spark occurs. Sounds like a mindnumbing process.
 

gkent

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It is my understanding that as timing is advanced, it moves the rotor further away from the terminal it is firing,
In a vacuum advance distributor the rotor/cap position does not change, it is the pickup plate that is moved.
 

gkent

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I guess I should clarify that in my case, the timing is locked.
So the timing is controlled by the ignition system ??

If so, the manufacturer should have provided a spec to phase the rotor to optimize the spark through the rpm range.

Just for the hell of it...

Let's say you have a 4" dia. cap.
Multiply by 3.1416 to get the circumference = 12.56"
divide the circ. by 360 to get inches per degree = .035" per degree
divide the circ. by 8 to get the spacing between posts = 1.57"

Now:
Let's say that at 12 deg initial the rotor is perfectly aligned with the post.
Let's say we want 35 degrees total
This means the system will fire 23 degrees sooner
23 x .035" = .80"
So at full advance the system would fire half way between two posts.

Hmmm !!! Not sure I like a "locked out" system.
 

451Mopar

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So the timing is controlled by the ignition system ??

If so, the manufacturer should have provided a spec to phase the rotor to optimize the spark through the rpm range.

Just for the hell of it...

Let's say you have a 4" dia. cap.
Multiply by 3.1416 to get the circumference = 12.56"
divide the circ. by 360 to get inches per degree = .035" per degree
divide the circ. by 8 to get the spacing between posts = 1.57"

Now:
Let's say that at 12 deg initial the rotor is perfectly aligned with the post.
Let's say we want 35 degrees total
This means the system will fire 23 degrees sooner
23 x .035" = .80"
So at full advance the system would fire half way between two posts.

Hmmm !!! Not sure I like a "locked out" system.
The timing degrees are at the crank, only 1/2 at the distributor (0.40), and if you the rotor at around 24 degrees, then the rotor phase is off 0.20 one side at idle, and 0.20 off the other side at 35 degrees, but still the rotor phasing will change when a computer is adjusting timing with a locked distributor.
The Full advance swing (excluding vacuum advance) of 23 degrees crank or 11.5 (just make it 24/12 to make the math easier) distributor. Split the rotor rotor phasing so worst case, the rotor is off center by about 6 degrees off either way from the cap terminal (the 0.200").

With the locked dist and computer controlled timing, you want the rotor phase to be aligned with the cap terminal just a bit before total advance WOT (no vacuum advance.)
This puts the majority of the rotor closer the the terminal from idle to Max RPM under WOT. At the vacuum advance, higher timing, the rotor can be slightly more offset.
With modern ignition systems, the cap/rotor relationship is a limitation. That is why you only get multiple sparks from a MSD from idle to around 3,000 RPM.
Most new cars use coil on plug, or coil near plug, and eliminate the cap/rotor distribution problem.
 

HEMI-ITIS

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Also when timing is taken out by any timing retard it effects the firing angle at the cap post. Phasing the rotor will keep the spark travel closest to the cap post when spark occurs when it is most critical.
 

dvw

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Think about this. Factory intial timing is usually 5 btdc give or take. With mechanical factory advance, timing can easily to 30 degrees. The blade on a factory rotor is wide enough to allow this amount of advance with no issue. Want to know for sure? Drill a hole between the coil terminal and the number 1 position in the cap. Point the timing light down thru the hole at the rotor. You'll be able to see exactly what you have. Rotor phasing has zero input on when the coil fires. You just need to make sure there is surface are between the rotor blade and the cap terminal. The leading edge of the blade should start somewhere near the begining of the distributor terminal is it isn't locked to aloow for mechanical advance. If it's fixed shoot for the center. But to be honest, unless it's way off it won't bother anything.
Doug
 
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