Do you have a reference for this? Everything I have ever read states that you do not want a large air gap. The MSD phasing video even clearly shows that a large gap creates very erratic spark, while the closer gap is a cleaner fuller spark. Doesn't the larger gap create premature erosion on the rotor and cap tower as well?
Reluctor and Phasing....
- Thread starter JoeSBP
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Do you have a reference for this? Everything I have ever read states that you do not want a large air gap. The MSD phasing video even clearly shows that a large gap creates very erratic spark, while the closer gap is a cleaner fuller spark. Doesn't the larger gap create premature erosion on the rotor and cap tower as well?
KitCarlson
Well-Known Member
The spark gap wastes energy. The secondary is a series circuit, if plug gap and rotor gaps are nearly the same, they get half, and the spark duration decreases with increased gap.
To verify, scope with 1kV probe is used the view coil- signal. The peak of the signal is where spark initiates, then there is the spark duration, it decays with time. Viewing from coil- is safer than attempting secondary measurement with 50kV probe. The ionized voltage of spark in gap is fairly low, typically 50 to 100V, the coil turns ratio is used to arrive at the estimated voltage. Experimenting by increasing gap, shortens spark duration. In a normal system spark duration is typically 1 to 3 ms. That is one reason for tracking on cap terminals. At higher RPMs spark duration stops early, when coil is recharged.
Modern ignitions use a coil per plug to eliminate rotor losses and other issues.
To verify, scope with 1kV probe is used the view coil- signal. The peak of the signal is where spark initiates, then there is the spark duration, it decays with time. Viewing from coil- is safer than attempting secondary measurement with 50kV probe. The ionized voltage of spark in gap is fairly low, typically 50 to 100V, the coil turns ratio is used to arrive at the estimated voltage. Experimenting by increasing gap, shortens spark duration. In a normal system spark duration is typically 1 to 3 ms. That is one reason for tracking on cap terminals. At higher RPMs spark duration stops early, when coil is recharged.
Modern ignitions use a coil per plug to eliminate rotor losses and other issues.
jos51700
Green Bearing thread connoisseur
Not sure if I'm reading this correctly
If I'm not mistaken, Neon had the first production DIS.
If I'm not mistaken, Neon had the first production DIS.
BillGrissom
Well-Known Member
Sorry, I have to pile on. You are probably thinking about the larger the gap at the spark plug, the better. That is why most new cars have ~60 mil gap vs 35 mil with points. But, to jump that gap, you need a better ignition system - both ECU and coil, which is what the Mopar 1970's ECU and GM's 1980's HEI gives. A few years back, Ford even considered using the head gasket as a spark plug, w/ fingers to make the spark jump all the way across the cylinder. As Kit says, any sparking inside the distributor cap is wasted energy, and one reason all modern engines use distributor-less ignition.
AJ/FormS
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Well Bill, I know you're a pretty smart guy, and I'm not trying to picka fight but I just gotta disagree;
I think they use COP cuz they can make cheapo-coils and charge you 55 bucks every time one fails, and they fail with alarming regularity. But more importantly the new style plugs have a much lesser voltage requirement which makes the COPs even possible in the first place. Those little teensy coils are IMO, junk. There is no power in them. But there doesn't have to be on account of every cylinder gets its very own.
But if you have a real engine, like an American V8, with a real coil that you might be able to weld with, then you can have real sparkplugs, with really big gaps so you can raise the voltage and pump some amps into the charge. And then when you might have a lil extra gap in the dizzy, the spark that actually jumps across there has no place to go,cuz the rotor is already gone. So when it gets to the plug it makes a flaming hot fire-starter and you can dial back the cruise fuel to make 32mpgs. I mean think about it; how big a gap can you realistically make in the dizzy,before it arcs to the wrong place, versus how little a gap can you make inside there? The difference is not very much,indeed.
Anyway that's my opinion, and since this philosophy gets me 7200 plus,and 93 in the 1/8th,and all-day idle, with no MSD in sight, Ima sticking to it,lol.
Accell sq top, you can take that buzzer to the bank.
I have just two nice things to say about COPs; 1) if one fails you can still drive the car home, and 2) it cleans up the underhood pretty good
I think they use COP cuz they can make cheapo-coils and charge you 55 bucks every time one fails, and they fail with alarming regularity. But more importantly the new style plugs have a much lesser voltage requirement which makes the COPs even possible in the first place. Those little teensy coils are IMO, junk. There is no power in them. But there doesn't have to be on account of every cylinder gets its very own.
But if you have a real engine, like an American V8, with a real coil that you might be able to weld with, then you can have real sparkplugs, with really big gaps so you can raise the voltage and pump some amps into the charge. And then when you might have a lil extra gap in the dizzy, the spark that actually jumps across there has no place to go,cuz the rotor is already gone. So when it gets to the plug it makes a flaming hot fire-starter and you can dial back the cruise fuel to make 32mpgs. I mean think about it; how big a gap can you realistically make in the dizzy,before it arcs to the wrong place, versus how little a gap can you make inside there? The difference is not very much,indeed.
Anyway that's my opinion, and since this philosophy gets me 7200 plus,and 93 in the 1/8th,and all-day idle, with no MSD in sight, Ima sticking to it,lol.
Accell sq top, you can take that buzzer to the bank.
I have just two nice things to say about COPs; 1) if one fails you can still drive the car home, and 2) it cleans up the underhood pretty good
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Looks like the only thing I can say is the vacuum adv rotates the pick up coil but the mechanical advance rotates the rotor. If you line up the rotor and the post when it advances it pulls away from the post in the wrong direction. I run a old school mopar performance dist w/tach drive.
3400 lb car w/me in it, 340 .572 cam stock engine, cast pistons the whole 9 yards. 11.80 and 115 mph with 40 deg total. 7600 through the traps, put 10,000 miles on it on the street and raced it probably 6 -10 times a year. Mostly ran 32 -34 on the timing. I think I agree with AJ
3400 lb car w/me in it, 340 .572 cam stock engine, cast pistons the whole 9 yards. 11.80 and 115 mph with 40 deg total. 7600 through the traps, put 10,000 miles on it on the street and raced it probably 6 -10 times a year. Mostly ran 32 -34 on the timing. I think I agree with AJ
So are y'all saying that you intentionally phase your rotor to the cusp of scatter, or are you saying that you have always had great repeatable results without ever concerning yourself with rotor phasing?
Think about what you said? if you pull more advance with the vacuum unit it rotates the pick up only, so now the shaft that the rotor & the reluctor are on has to rotate further to line up with the pick up coil you just moved. that changes the distance from the post to the rotor.
If you think about it the posts are 45 degrees apart. How many degrees does the rotor turn from initial to full advance. Depending on your set up 25 - 30 degrees? No vac adv 13 - 18?
1)If the rotor tip is aligned w/the terminal post in the dist. cap when either the reluctor blade is aligned w/the pick-up core, or when the breaker points just open, it will always stay
phased that way if you only run mech. advance. The relationship between the pick-up and cap never changes, which determines phasing.
2)If you are running vacuum adv., the position of the rotor will move away from the post the opposite direction of the shaft's rotation, just like the timing mark on your damper in
relation to the -0- on the cover as spark advances. Any electronic advance system should be treated the same as vacuum in this regard.
3)If you are running a lot of vacuum/elec. adv., and you're worried the rotor tip is getting too far away, you could re-phase the rotor(in this case clockwise) so that the advance
will bring the tip "back" to perfect alignment under adv., but under full throttle it will revert to wherever it is phased "static".
phased that way if you only run mech. advance. The relationship between the pick-up and cap never changes, which determines phasing.
2)If you are running vacuum adv., the position of the rotor will move away from the post the opposite direction of the shaft's rotation, just like the timing mark on your damper in
relation to the -0- on the cover as spark advances. Any electronic advance system should be treated the same as vacuum in this regard.
3)If you are running a lot of vacuum/elec. adv., and you're worried the rotor tip is getting too far away, you could re-phase the rotor(in this case clockwise) so that the advance
will bring the tip "back" to perfect alignment under adv., but under full throttle it will revert to wherever it is phased "static".
Uh, Genital Motors was using DIS in the late '80's, gawdawfull as they could be sometimes. But they were first in 'merica.
Incorrect, both plugs fire simultaneously, the cyl on the exh. stroke takes very little tension to jump the gap. The pairs also fire w/ the same polarity every time.
Want proof take a set of loooong overdue plugs out, half have the "pos" electrode burned to the insulator, and the other half have the "grd" electrode burned to a
tapered little wedge.
Rapid Robert
Well-Known Member
What Killer 6 said, only vac adv changes RP (shifts it CCW on a SB). You can easily duplicate the machined reluctors that Andy Finkbeiner originally machined that Eberg bought up, drill the new roll pin hole in a bit from the ID then open it up to the ID with a quality mini rattail file OR dremel out the plastic locating tang inside the rotor cavity & reclock it correctly & hold it in position then drill thru the rotor and dist metal shaft horizontally then lock it that position with a small bolt/nut OR cut a new locating groove in the dist shaft to relocate the rotor plastic tang OR widen the current dist shaft groove and JB weld up the other side to restore the original width. (1) degree of rotor movement is .024" around the circumference so a 10 deg can will shift it about a 1/4" inch. cap terminal width is .214" and rotor terminal width is .244" so if you have the rotor clocked about halfway "across" the cap terminal (on the CW side) the can will shift it back CCW till it is about halfway "off" the cap terminal on the other side. this is good contact interface. For a performance app you want the rotor to be in close proximity to the cap terminal at WOT when the required voltage is the greatest (most compression) and the available voltage is the least (coil saturation time is the shortest). keep the terminals clean and sharp as it takes less voltage to jump across sharp terminals than it does smooth/dulled surfaces, dremel them to restore em. Next is rotor tip TO the vertical part of the cap terminal which should be ~.015". there is a NAPA "Echlin" rotor a MO3000 which has a .060" longer blade for $8 & change out the door OR drill out the rivet & make your own blade for the right clearance. reduce lower shaft axial play to .005" & speedway motors has a cheap shim kit or use others but get ones with no bevel on the ID/OD on one side which alot of common washers have. the $22 FBO plate is the by far the best bang for the buck to alter the mechanical advance amount, has slots for 10-12-14-16-18 crank degrees. get a tan cap with ribbs underneath and BRASS not aluminum terminals. Lowes has bronze bushings for cheap and Grainger has an adj 7/16 to 9/16 reamer for cheap. toss the OE heavy spring with the elongated loop & sub in a lighter one (mr gasket/MP/transdapt or even a chebby) along with the OE lighter one for a start. adj the initial/total/springs/vac can IN ORDER (more on that later). Several 1/2" holes in the top/sides of the cap flat lets ionized air molecules escape (reduces crossfire potential) and lets you check RP (drill one on top halfway inbetween the center and the #1 cap terminals & shine your light straight down on it to check). Use the C=Pi times diameter for the math as needed. The # on a particular can is in dist degrees. RR
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I just want to add this to the electronic advance comment I made, if the advance system is computerized, many have you set the initial timing to the MAXIMUM advance and
the computer RETARDS it to the "base" timing! Keep that in mind if you're running such a system & still sending the spark thru a dizzy(why?), it is the WORST thing to phase
for, because ALL of the advance changes the phasing.
the computer RETARDS it to the "base" timing! Keep that in mind if you're running such a system & still sending the spark thru a dizzy(why?), it is the WORST thing to phase
for, because ALL of the advance changes the phasing.
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