Using a Dual point distributor... What is the benefit?

I searched here and on several different sites but I didn't get an answer (or an answer I could understand) so here goes.....


Maybe I am "over thinking" this?? But what is the purpose of having a set of --dual points-- in a distributor??? A single set of points open up (with DWELL being the factor of how long or short they stay open), which causes the coil to lose its ground, generating a high-voltage pulse, which in turn transfers voltage thru a rotor and into a spark plug wire, then to a sparkplug which ignites a cylinder........ so if you have ONE (1) coil wire going into the top of a distributor cap and the point(s) open and close causing it to "operate" what does a "second" set of points do to help out??? I just can't figure this one out in my head?!?!?!? I am sure it is JUST ME!!!!! but maybe someone else is wondering too?????
Thanks, Ken

 

dual points is so the points can stay shut longer thus more coil saturation.. hotter spark.

 

http://mgaguru.com/mgtech/ignition/ig200.htm
About 1/2 way down
1st set makes, 2nd set brakes
Possibly better stability
Only one I ever ran was in a bug,


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I believe the points opening slightly overlaps each other delivering a longer spark. One opens on one cam lobe and the other set opens on the oposite side but slightly later than the first set so the time the points read open is extended.

 

O.K.... and forgive me....... as I AM NOT BEING A SMART ASS!!!! (I am just not understanding!!) ....... but if the points open and close at the same time simutaneously since the are both being operated on the "exact opposite" lobes yet equal distance apart on the distributor how are they staying shut longer???


...edit... couple of posts during my reply... Maybe they don't open simutaneously?!?!?! that may be why I didn't understand????

and Thommyknocker Thank you!!! A fellow "rockstar" right!!! Good info there, I searched a LONG time before I asked and never came up with that info!!!!! Thanks, Ken

 

First there are 2 styles of dual points - each claiming different advantages.
Speaking on a typical V8 you can have a 4 lobe distributor or a 8 lobe.

On the 4 lobe the advantage claimed was increased RPM since each point set opens 1/2 as much (speed wise) so where you might get point bounce at 7,000 rpm you could now theoretically extend that to 14,000. I could also see extended life since each one works less times. On the 4 lobe - each point only fires every other cylinder.

On the 8 lobe you get increased dwell. I believe this is about being physically able to get the points open and closed quicker - meaning the ramp portion. Simply re-grinding the lobe probably has practical limits where you can no longer increase the "steepness" of the lobe without risking point bounce. By staggering the point sets and overlapping them - you extend this without having to get super agressive on the lobe angle. Same reason why they go to larger diameter roller lifters when you get to super high lift cams.

Well that's my take, but I'm no expert.

 

what I can't figue out is why most people think HEI stands for High Energy Ignition when it actually stands for Hall Effect Induction. A magnetic field triggering device rather than an energy dilivery system???

but any way here is a primer on mallory dual points variations

http://mgaguru.com/mgtech/ignition/ig200.htm

 

hei, cause somebody used it to advertise, and went from there, people don`t know what hall effect is.......whats the advantage of a dual point dizzy......lost of beer while you get the points adjusted properly.......lol

 

What he said, better coil saturation hence hotter spark.

 

No real benefit on the street. I had a dual point for a couple of years and getting two sets of points properly adjusted and keeping them there was a major pain.

A couple of years ago I replaced them with a Pertronix and haven't had the distributor cap off since!

 

Coil saturation is the main benefit. I have never had to run dual points, I have run dual mags on other stuff, but I usually run an HEI or Pertronix-Type systems.

 

There are two kinds of dual point systems. In one kind each contact set serves four cylinders, which in theory the points will last twice as long before needing replacement. This offers no "performance" gain.

The other kind uses both points in tandem for each cylinder. The points act at nearly but not exactly the same time. There is overlap or a "handoff", meaning that the contact made between the power supply and the coil stays longer, leading to a higher saturation or "charge" in the coil, leading to a higher voltage spark. (by the way, there's no such thing as a "longer" spark, if "longer" means time, but a higher voltage spark can travel a longer distance over a bigger gap).

Think of it like this, you have Points A and Points B, as the cam turns, Points A reach the low spot first (they Close) and get charged while on the low spot. B follows and continues the circuit. Turn more and Points A reach the high spot and open, but B isn't there yet so the circuit is still closed. When B reaches the high spot the circuit is opened and the coil fires.

Like this:

AAAAAABBBBBBB FIRE!

Hope this helps.

 

^^^ Excellent makes sense to me now. Thanks guys, again the wealth of knowledge here is amazing...Ken

 

Actually, should be more like aaaa/ba/ba/bbbb FIRE!

 

One truly important question...
Will a Pertronix kit for a single point Chevy bolt into an 8 lobe dual point Distributor???

 

Pertronix makes kits to fit Mallory dual point distributors.

 

Nope !! You need either a eight lobe or 4 lobe Mallory kit.from pertronix......

 

...................

 

All dual point lack vaccum advance?

 

no , not all...i have an Accel dual point distributor with vacuum advance sitting right here.

 

Hall effect induction predated GM's Co opting of it to give a marketing name to thier system.

 

Except the HEI isn't a hall effect type ignition. Really. Hall effect sensors do away with the slight magnetic "lurch" you get with a typical magnetic pickup trigger (like the HEI).

Oh, and the purpose of dual point ignitions is primarily to double the amount of current going to the coil. Remember the ballast resistor? It's there to keep the current down and prevent the points burning as they make and break. 2 sets of points= double the primary current= faster and better coil saturation.

 

except with electric points you are unable to deduce a bad coil or ignition on your own under the hood.

 

I'll add that dual points can be wired so that the set of points that opens first can be tied to a simple switch so that they can be turned off. This in effect will allow the ignition timing to be retarded at the flip of a switch. This was advantageous on the drag cars where advanced timing could be used in first and second gears and then the timing simply retarded by turning off one set of points when going to third gear. Careful placement of a push/pull switch on the dash just in front of the shifter could have this switch turned off with the 'knuckles' when shifting to third when using a four speed tranny.

 

I can't recall anyone ever using the acronym H.E.I. for Hall Effect Induction when relating to automotive ignition. When Edwin Hall discovered the phenomenon in the 1800's, it was named the Hall Effect after him and through out history most application of the theory have been known as Hall Effect Sensors. It is certainly what we have called them when used in our ignition products here at PerTronix.
In most automotive uses a Hall effect is still a triggering device not an energy delivery system. Hundreds of millions of integrated Hall circuits are in use, mainly as contactless switches, and mechanical proximity sensors. Another application of a sensor is a current measuring transducer.
Regardless of that, since HEI was indeed trademarked by GM and has become the standard accepted definition for that acronym, it is why just about everyone uses HEI to mean High Energy Ignition.

 

Simply incorrect !!! The dual points have nothing to do with the primary current, only the dwell time allowing the coil to build a magnetic field.
Primary resistance changes primary current , lower the resistance and the current is increased .

 

Umm, yeah. Back up, engage brain...path of least resistance...ok.

Guess you'd need 2 of everything in that case. Thanks for putting me back on the path!

 

nice volley...er ...thread guys....l

 

Actually, Mallory made a conversion kit with the same basic idea for some Mopar distributors in the late '50s/early '60s. The biggest advantage of running an aftermarket dual point distributor in a '49-'53 flathead was that they had a real advance system, unlike the all vacuum system that the stock distributor had. Of course, there are modern ignition systems that have made the dual point setup obsolete, but there are also lots of engine designs that have made flatheads obsolete, so we'd better not run them anymore either..........right?
As to those of you who found setting and keeping dual points in spec a hassle, I don't understand what the problem is/was. I've run them in several cars over the years and found them to be no more trouble than a stock single point distributor.

 

Playing around here in the old threads and was just wondering if anyone might want to chime in regarding the dual Mallory dual point performance enhancement over a stock distributor. Is there actually any benefit to running one over factory?
Thanks,
Mark