Why dual points?

[BLUPORT]

That's funny... I don't really hang out there, but I've read enough of their threads to see they tend to diagnose problems as opposed to throwing parts. I imagine that's because of the prohibition on whiz-bang shinola post 1965, but I didn't know it was an actual policy.

Yeah, I found out the hard way when I joined there, and posted an intro, then got spammed with flaming insults via PM for being a moron who can't read the rules in the one buried post about it.

 

[Carmine]

A train wreck it may be, but it's my train wreck. Car was headed for a crusher when I decided to buy it.

Yup. Daily driver. I have no interest in owning something I can't or don't use. I'm not running a museum.

By train-wreck, I mean the firing line of answers completely unrelated to your issue, not your car. I don't feel like I could even get a question in about your fuel leak before it gets buried under suggestions for a new method to energize the coil, so that's why I'm not in the thread.

Trust me, I'm the last guy who'd tell you that you can't drive the car everyday. You most certainly can. The physics of suck-squeeze-bang-blow haven't changed. But I would say if you're new to this "era" of automobile, there IS a learning curve. And that could prove very frustrating if you must rely on any-era car that was one step from the scrapyard.

I wish you good luck and patience. Be hesitant to introduce new variables when troubleshooting a problem. Read some old auto shop text books from that era and learn how these systems work.

 

[70bigblockdodge]

I wish you good luck and patience. Be hesitant to introduce new variables when troubleshooting a problem

K.I.S.S.

 

[PontiacJim]

Just saw a CL ad for a dual points distributor. Why dual points? Is it a fail safe?

Mopar big block dual points distributor.

Great question, just seems like a lot of BS you have to deal with to get your answer.

Dual Points were used in hi-performance applications, whether a factory hi-performance car or aftermarket street/strip/race cars. You could have a dual point distributor set-up/manufactured as such, or purchase a dual point breaker plate and swap it out on a single point distributor.

Each set of points could be either tied into a single condensor or with many aftermarket dual points, each set of points had its own condensor and these were often mounted on the outside of the distributor housing as they were bigger in size than your typical factory type condensor.

Dual points provided more dwell time. Dwell is the length of time the coil is turned on, so dual points keeps the coil turned on longer, ie longer spark. With one set of points closing to complete the circuit and the other set opening to break the circuit, it provides a longer dwell or coil saturation time. This enables the coil to build a stronger magnetic field and produces both a hotter and higher voltage secondary spark. The 409CI Chevy with factory Mallory dual points, spec'd each set of points individually using a Dwell Meter to obtain 29 degrees of dwell (which is about the same spec for a single point distributor), but with both operating, they gave you a combined dwell of 33-34 degrees - so you can see the difference provides a longer spark time.

Dual points allows the ignition coil to produce higher voltage at higher engine RPM's. It also allows for a lighter weight set of points with corresponding spring tensions taylored to higher RPM's to reduce point bounce. Too high a tension on the spring can cause the points to hit the distributor's cam at high RPM's and bounce. Too light a tension on the spring at high speeds and they can "float," or stay open.

Dual point distributors are typically used in high performance engines where the engine is meant to best perform at wide open throttle (WOT). So the vacuum advance found on most distributors is eliminated. Vacuum advance only works when there is engine vacuum present which is typically at lower speeds and part/light throttle. Factory hi-performance cars were aimed more for all out racing and wide open throttle blasts, so no need for a vacuum advance. Of course drag engine are designed for WOT, so again, no use for vacuum advance.

The dual points use centrifugal advance via a set of weights. The advance curve is much easier to dial in using just the centrifugal advance of the weights. Different springs having various spring tensions that can be used to control the weights used for centrifugal advance to tailor the advance curve to the engine/car. You can also use different weights. The advance curve is typically done on a distributor machine - often made by Sun. However, you can do this yourself using a dial-back timing gun and noting the RPM the total timing comes in using the mechanical advance and, vacuum advance disconnected. In the past when you had high compression street engines and high octane leaded gas, many would shoot for total advance to be in by 2500 RPM's.

The use of solid core spark plug wires also aided in delivering a hotter spark, but created a bunch of static on your radio unless you added a radio suppression kit. This is why most spark plug wires are of the resistance type wire. Today's wires are much improved.

Some of the distributors had a provision for a cable drive much like a speedometer cable and was used to drive a mechanical tachometer for more accuracy. Cable driven tachometers were not limited to hi-performance use or race cars as some trucks used a cable driven tachometer and suspect your older "antique" cars if equipped with a tachometer used a cable drive.

Dual Point distributors phased out by the mid-70's with the introduction of electronic ignition and things like the MSD aftermarket ignition upgrades.

 

[70bigblockdodge]

Great question, just seems like a lot of BS you have to deal with to get your answer.

Dual Points were used in hi-performance applications, whether a factory hi-performance car or aftermarket street/strip/race cars. You could have a dual point distributor set-up/manufactured as such, or purchase a dual point breaker plate and swap it out on a single point distributor.

Each set of points could be either tied into a single condensor or with many aftermarket dual points, each set of points had its own condensor and these were often mounted on the outside of the distributor housing as they were bigger in size than your typical factory type condensor.

Dual points provided more dwell time. Dwell is the length of time the coil is turned on, so dual points keeps the coil turned on longer, ie longer spark. With one set of points closing to complete the circuit and the other set opening to break the circuit, it provides a longer dwell or coil saturation time. This enables the coil to build a stronger magnetic field and produces both a hotter and higher voltage secondary spark. The 409CI Chevy with factory Mallory dual points, spec'd each set of points individually using a Dwell Meter to obtain 29 degrees of dwell (which is about the same spec for a single point distributor), but with both operating, they gave you a combined dwell of 33-34 degrees - so you can see the difference provides a longer spark time.

Dual points allows the ignition coil to produce higher voltage at higher engine RPM's. It also allows for a lighter weight set of points with corresponding spring tensions taylored to higher RPM's to reduce point bounce. Too high a tension on the spring can cause the points to hit the distributor's cam at high RPM's and bounce. Too light a tension on the spring at high speeds and they can "float," or stay open.

Dual point distributors are typically used in high performance engines where the engine is meant to best perform at wide open throttle (WOT). So the vacuum advance found on most distributors is eliminated. Vacuum advance only works when there is engine vacuum present which is typically at lower speeds and part/light throttle. Factory hi-performance cars were aimed more for all out racing and wide open throttle blasts, so no need for a vacuum advance. Of course drag engine are designed for WOT, so again, no use for vacuum advance.

The dual points use centrifugal advance via a set of weights. The advance curve is much easier to dial in using just the centrifugal advance of the weights. Different springs having various spring tensions that can be used to control the weights used for centrifugal advance to tailor the advance curve to the engine/car. You can also use different weights. The advance curve is typically done on a distributor machine - often made by Sun. However, you can do this yourself using a dial-back timing gun and noting the RPM the total timing comes in using the mechanical advance and, vacuum advance disconnected. In the past when you had high compression street engines and high octane leaded gas, many would shoot for total advance to be in by 2500 RPM's.

The use of solid core spark plug wires also aided in delivering a hotter spark, but created a bunch of static on your radio unless you added a radio suppression kit. This is why most spark plug wires are of the resistance type wire. Today's wires are much improved.

Some of the distributors had a provision for a cable drive much like a speedometer cable and was used to drive a mechanical tachometer for more accuracy. Cable driven tachometers were not limited to hi-performance use or race cars as some trucks used a cable driven tachometer and suspect your older "antique" cars if equipped with a tachometer used a cable drive.

Dual Point distributors phased out by the mid-70's with the introduction of electronic ignition and things like the MSD aftermarket ignition upgrades.

I'm pretty sure that was mentioned.