Rotor Phasing

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pjc360

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This is kind of a long story so I'm
Going to attempt to keep it short and sweet.
91 Dodge w150 short bed 4x4 Truck.
300hp crate 360 Magnum, around 20-25k miles on engine.
Was running a Mopar distributor from FBO systems, kept having issues with the advance plate wobbling around, reluctor teeth smacking the pick up coil post.
Long story short I ditched that unit and bought a firecore 50 electronic vacuum advance unit.
First firecore unit ran extremely rough at 2500 rpm with initial timing at 18 degrees and total timing at 34 degrees and an additional 12 degrees from vacuum advance.
When I dis-connected the vacuum advance the (rough spot went away)
That led me to believe it was a rotor phasing issue.
So I drilled a 5/8 hole behind the number one tower on a spare distributor cap I had laying around and checked the rotor.
Sure enough it was out of phase.
Sent the unit back to firecore and firecore sent me a second unit.
Checked the phase on the second unit and the rotor still isn't directly under cap terminal but it is much closer then the first unit was.
I noticed the rough spot was a lot better at 2500 rpm but it's still slightly there.
I bought a modified reluctor from Rick ehrenberg and I have the reluctor in my shop.
I'm considering installing it at the 5 degree behind a tooth slot to move the rotor forward a little more.
Below is a pic of where my rotor is with 18 degrees initial and 34 degrees total with an additional 12 degrees of timing added at idle for a total of 30 degrees of idle timing.
If you turn the picture upside down that hole is directly behind the number one cap terminal.
Is this close enough? Or could it be better?
Everything I've read says the rotor tip should be directly inline with the cap terminal and in the pic you can clearly see the rotor tip is not quite yet under the cap terminal but the edge of the rotor is just starting to come into contact with the cap terminal.
I'm trying to get eliminate this rough spot I get between 2500-3000 rpm and I believe this is the answer.

IMG_2688.PNG
 
That might be OK if the vacuum advance will move it towards the tower as it comes on. You can connect a Mighty-Mite hand vac to easily test that. Note that vacuum advance moves the phasing, whereas the centrifugal advance doesn't since that angular shift occurs below the reluctor wheel pickup.

Sounds like the 91 Magnum engines still used a distributor for spark timing vs later ones which use a crank pickup and computer. But I am surprised they still used a mechanical pod for vacuum advance since my 1982 Aries had that in the "spark computer". Perhaps you are using a 1970's Mopar distributor.
 
BillGrissom said:
That might be OK if the vacuum advance will move it towards the tower as it comes on. You can connect a Mighty-Mite hand vac to easily test that. Note that vacuum advance moves the phasing, whereas the centrifugal advance doesn't since that angular shift occurs below the reluctor wheel pickup.

Sounds like the 91 Magnum engines still used a distributor for spark timing vs later ones which use a crank pickup and computer. But I am surprised they still used a mechanical pod for vacuum advance since my 1982 Aries had that in the "spark computer". Perhaps you are using a 1970's Mopar distributor.
Click to expand...

This is a Mopar Crate carbureted 360 Magnum, the 300hp version.
The position of the rotor in the picture is with vacuum advance.
In the picture that's the engine idling with 18 degrees of initial timing plus 12 degrees from vacuum advance:
I have the vacuum advance routed to manifold vacuum source to get more advance at idle.
So that's 18+12 equals 30 degrees at idle.
So when the vacuum advance goes away the rotor should then move closer to the cap terminal and when the vacuum advance is on it pulls the rotor ccw from the cap terminal. Like how it's pictured right now.
 
The ideal thang is for the rotor be be on "one side" of the contact with no vacuum, and about equal to the opposite side when the vacuum is all in. Properly adjusted for phase, change in mechanical advance should not affect phasing
 
67Dart273 said:
The ideal thang is for the rotor be be on "one side" of the contact with no vacuum, and about equal to the opposite side when the vacuum is all in. Properly adjusted for phase, change in mechanical advance should not affect phasing
Click to expand...
So are you saying its within range in the picture with the vacuum advance?
 
I can't tell what you have there It would depend on which way it moves from that point.
 
67Dart273 said:
I can't tell what you have there It would depend on which way it moves from that point.
Click to expand...
67Dart273, you have to turn the photo upside down to see it correctly.
When you do that you'll see that the rotor is slightly to the right of the cap terminal, when the vacuum advance backs off when you get in the throttle obviously the rotor would then swing back to the left going towords the cap terminal.
 
Why don't you just DESCRIBE IT?

If the rotor moves towards the desired contact when you activate the vacuum, then yes you are on the right track. How am I supposed to tell all that from a still photo?
 
I had someone tell me the rough spot I'm feeling around 2500-3000 rpm is because the advance rate is coming inn too quickly.
Right now with 16 degrees of mechanical advance and the initial timing being at 18 degrees and the total timing being at 34 degrees with the springs that are in the distributor that advance starts to come in around 1200 rpm and is all in by 2400-2500 rpm.
This is on a 300hp crate 360 mgnum with an advertised compression ratio of 9:0.1 running premium 91 octane eathanol free fuel in a 91 w150 short bed 4x4 truck with a 4 inch suspension lift and 33 inch tires with 4.56 gears.
Is that too quick of an advance rate for this combination?
I forgot to add I'm also at 3200 feet above sea level, I know that has an affect on timing and advance rate.
The person i was talking too reccomended slowing the advance rate down to around 3000-3200 rpm.
My thought on it was with the lower compression ratio and the premium fuel and the higher elevation with lower 4.56 gears that all in by 2400-2500 shouldn't really be an issue.
But then again I haven't really played with different spring combo's and don't know everything when it comes to tuning a distributor and setting up the curve.
 
67Dart273 said:
Why don't you just DESCRIBE IT?

If the rotor moves towards the desired contact when you activate the vacuum, then yes you are on the right track. How am I supposed to tell all that from a still photo?
Click to expand...

I just figured if you looked at the photo you'd see what I'm talking about.
It's a small block, so the distributor is spinning clockwise.
When you have the photo turned upside down you can see that with the vaccum advance activated the rotor is pulling away from the cap terminal ccw, then when throttle is applied and the vacuum advance backs off the rotor would then go cw towords the cap terminal.
Sorry not trying to irritate you.
 
So quick update, I decided to increase the mechanical advance from 16 degrees to 20 degrees to slow the advance rate down a little bit to see if that would make a difference.
Set mechanical advance to 20 degrees which allows timing to be all in by around 2600-2800 rpm.
Based on the chart that came with the distributor, it was coming all in around 2400 at 16 degrees of mechanical advance.
Set initial at 14 and total at 34 took it out and to my suprise it behaved much better....
The rough spot was almost completely gone that I was getting around 2500.
So the guy that suggested my advance curve was coming inn too fast was right.
Ether that or it likes having a little more mechanical advance or a little less initial timing.
I didn't change the vaccum advance at all, the only thing I changed was the mechanical advance from 16 to 20 which of course slowed the advance rate down a couple hundred rpm, and of course I had to lower the initial timing 4 degrees to maintain my total of 34.
So now I have to figure out a spring combination that will have the timing all in around 3000 rpm.
Looking at all the spring combo's that came with the distributor nothing slows it down to around 3k, it's ether 2600-2700 or it jumps all the way to 3500-3600 with one spring swap.
 
the crane kit in the chart is no longer available but here is some info

398.jpg
EDIT A person can grind a bit off of the weight "tips" to slow the curve to dial it in further
 
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