A question for the N gurus

[gwstang]

In reading the post below about the points, I got to wondering about why the gap opening has to be set differently for side-mount/front-mount, old VW's or anything that has points? Does it have something to do with duration maybe? Just interested and always willing to learn even at 57. Thanks, Gary.

 

[Bob]

IMHO, it has to do with cam profile... how "steep" the ramp is that opens the points.

IIRC, there's a considerable difference between the distributor cam diameter and profile between the front and side mounts.

 

[JMOR]

(quoted from post at 00:29:25 12/14/13) In reading the post below about the points, I got to wondering about why the gap opening has to be set differently for side-mount/front-mount, old VW's or anything that has points? Does it have something to do with duration maybe? Just interested and always willing to learn even at 57. Thanks, Gary.

f you examine the geometry of the two distributors, you will notice that on front mount the points follow the cam at a one to one ratio, whereas on the side mount the points open by about 1.6 times the cam movement of points rubbing block. Less energy is lost in the points arc and less arc means less point erosion.........both benefits of opening further faster. Evolution of design.

 

[Bill Crowell]

The geometry of the cam lobes and the point opening ratio merely determine the total dwell, or how long current flows in the coil primary. The front-mount distributor"s built-in coil requires 35-38 degrees of dwell and the separate coil on the right side of the engine on side-mount 8Ns requires 32 degrees of dwell. I believe this is because the primary of the front-mount coil has a higher impedance than the primary of the separate coil has, so current must flow through a front-mount coil's primary for a longer time to reach the same voltage peak.

 

[JMOR]

(quoted from post at 01:09:32 12/14/13) The geometry of the cam lobes and the point opening ratio merely determine the total dwell, or how long current flows in the coil primary. The front-mount distributor"s built-in coil requires 35-38 degrees of dwell and the separate coil on the right side of the engine on side-mount 8Ns requires 32 degrees of dwell. I believe this is because the primary of the front-mount coil has a higher impedance than the primary of the separate coil has, so current must flow through a front-mount coil's primary for a longer time to reach the same voltage peak.

'll have to take exception to that Bill. First, the ratio will not affect dwell. Only cam design & gap setting determine dwell. While I have never seen printed material specifying dwell for a side mount, since the NAA spec shows 35.5 to 39, I would not expect the 8N side mount to be significantly, if any different. Not significantly different from the front mount 35 to 38. Where did you get your quoted 32 number? As far as impedance of primaries are concerned, I have also never seen those numbers in specifications or other literature. Where did you get those & what are those numbers?

 

[Bob]

As slow as these engines run @ WOT, I DOUBT there's a problem with coil saturation time!

The old flatty V-8's, which used essentially the same ignition setup could rev MUCH higher than the governed tractor engine possibly can, and has twice as many cylinders/sparks per revolution.

What's "N" high idle, 2200?

At 2 sparks per revolution, that's 4400 sparks per minute.

One figure for redline of the flatty V-8 I saw was 3800 RPM, and with FOUR sparks per revolution, 15,200 sparks per minute.... almost THREE AND A HALF TIMES as many!

NOT much dwell TIME available for coil saturation at THAT rate, yet it works!

 

[L. B,]

Hey Gary what do you mean ? for gurus. All these guys are very Savvy but they learned that in Auto Shop 101, LOL.

 

[Bill Crowell]

I never said there was a problem with coil saturation time. I just said the coil primaries" impedances were different, so they required a different dwell.

 

[JMOR]

(quoted from post at 03:27:57 12/14/13) I never said there was a problem with coil saturation time. I just said the coil primaries" impedances were different, so they required a different dwell.

mpedance is a primary factor in saturation time. I feel certain that you recognize that or else why would you relate it to dwell time?

 

[Roger in Iowa]

Believe some of the old "flatties" V8s ran dual point distributors. So maybe they too needed longer dwell time.

 

[Bob]

(quoted from post at 04:17:06 12/14/13) Believe some of the old "flatties" V8s ran dual point distributors. So maybe they too needed longer dwell time.

You are correct. SOME did use double points.

Purpose, though, was point life. One set of points takes the arc when the points open, the other set takes the arc/load/contact bounce when the points close. Spreads the wear from use over TWO sets of points.

 

[gwstang]

(quoted from post at 23:42:07 12/13/13) Hey Gary what do you mean ? for gurus. All these guys are very Savvy but they learned that in Auto Shop 101, LOL.

Say, these guys are way out of my little minor league self...lol

 

[gwstang]

Very interesting info that ya'll provide on here. I like to see a little spirited back and forth on a subject as there is much to be learned from both sides. I appreciate the time that ya'll take to help me explore these things. I had always wondered why some of the Ford Mustangs (I have a '66) had single points dist. and some had the dual points dist. I believe the Hi-PO K codes all had the dual points just for the high performance factor. From what I have read on here, it was for the higher revving function...which the K Codes were famous for, up to 7K without even blinking! I also had a 1977 Honda 550F murdercycle (as my dad always called then...an accident looking for a place to happen. :shock: ) that had dual points and man would that thing get up and go. Good revving machine.

 

[L. B,]

I like kicking stuff around too if we all agreed all the time its not a learning process. Some of these guys forgot more then I know. Now you ask a tech ? that I have wondered about myself but not just what you ask but the entire int combustion engine is a very easy to understand on paper. But when you take just the little 4 cyl Ford engine the Ns have and you think what is going on at just at idle it is like thinking about the meaning of life. The gas into a cyl spark at the right time, valves going intake and close and exhaust open and do it time after time years on end. Then you think the points are moving 4X that fast and the coil loading up with juice at the speed of light I think its impossible what nut job thought this could ever work? But it does. L.B, Master of the Obvious

 

[oldtanker]

(quoted from post at 17:59:46 12/14/13)
Very interesting info that ya'll provide on here. I like to see a little spirited back and forth on a subject as there is much to be learned from both sides. I appreciate the time that ya'll take to help me explore these things. I had always wondered why some of the Ford Mustangs (I have a '66) had single points dist. and some had the dual points dist. I believe the Hi-PO K codes all had the dual points just for the high performance factor. From what I have read on here, it was for the higher revving function...which the K Codes were famous for, up to 7K without even blinking! I also had a 1977 Honda 550F murdercycle (as my dad always called then...an accident looking for a place to happen. :shock: ) that had dual points and man would that thing get up and go. Good revving machine.

Actually dual point systems on high performance engines is to help with the problem of points floating at higher RPMs to my understanding. With 2 sets of points you reduce the chance of high RPM misfire by 1/2.

It's kinda like the high performance "high energy" coils. When you start running high compression engines the pressure raises the resistance at the plug gap, hence the need for a higher voltage spark to over come the resistance. If your engine needs 7,000 volts to overcome resistance that "hot" coil is going to fire that plug at 7,000 volts, not at the advertised 45K or so. When the points close it completes a circuit that allows the coil to charge. When the points open the coil discharges building voltage until resistance is overcome. OK these old Fords about the only way to increase resistance is to gap the plugs wider or shave the head.

Someone will correct me if I'm wrong.

Rick

 

[gwstang]

(quoted from post at 00:08:28 12/16/13)

(quoted from post at 17:59:46 12/14/13)
Very interesting info that ya'll provide on here. I like to see a little spirited back and forth on a subject as there is much to be learned from both sides. I appreciate the time that ya'll take to help me explore these things. I had always wondered why some of the Ford Mustangs (I have a '66) had single points dist. and some had the dual points dist. I believe the Hi-PO K codes all had the dual points just for the high performance factor. From what I have read on here, it was for the higher revving function...which the K Codes were famous for, up to 7K without even blinking! I also had a 1977 Honda 550F murdercycle (as my dad always called then...an accident looking for a place to happen. :shock: ) that had dual points and man would that thing get up and go. Good revving machine.

Actually dual point systems on high performance engines is to help with the problem of points floating at higher RPMs to my understanding. With 2 sets of points you reduce the chance of high RPM misfire by 1/2.

It's kinda like the high performance "high energy" coils. When you start running high compression engines the pressure raises the resistance at the plug gap, hence the need for a higher voltage spark to over come the resistance. If your engine needs 7,000 volts to overcome resistance that "hot" coil is going to fire that plug at 7,000 volts, not at the advertised 45K or so. When the points close it completes a circuit that allows the coil to charge. When the points open the coil discharges building voltage until resistance is overcome. OK these old Fords about the only way to increase resistance is to gap the plugs wider or shave the head.

Someone will correct me if I'm wrong.

Rick

Interesting. If it has two sets of points, does it also have two condensers or coils? Why or why not?

 

[JMOR]

(quoted from post at 20:18:24 12/16/13)

(quoted from post at 00:08:28 12/16/13)

(quoted from post at 17:59:46 12/14/13)
Very interesting info that ya'll provide on here. I like to see a little spirited back and forth on a subject as there is much to be learned from both sides. I appreciate the time that ya'll take to help me explore these things. I had always wondered why some of the Ford Mustangs (I have a '66) had single points dist. and some had the dual points dist. I believe the Hi-PO K codes all had the dual points just for the high performance factor. From what I have read on here, it was for the higher revving function...which the K Codes were famous for, up to 7K without even blinking! I also had a 1977 Honda 550F murdercycle (as my dad always called then...an accident looking for a place to happen. :shock: ) that had dual points and man would that thing get up and go. Good revving machine.

Actually dual point systems on high performance engines is to help with the problem of points floating at higher RPMs to my understanding. With 2 sets of points you reduce the chance of high RPM misfire by 1/2.

It's kinda like the high performance "high energy" coils. When you start running high compression engines the pressure raises the resistance at the plug gap, hence the need for a higher voltage spark to over come the resistance. If your engine needs 7,000 volts to overcome resistance that "hot" coil is going to fire that plug at 7,000 volts, not at the advertised 45K or so. When the points close it completes a circuit that allows the coil to charge. When the points open the coil discharges building voltage until resistance is overcome. OK these old Fords about the only way to increase resistance is to gap the plugs wider or shave the head.

Someone will correct me if I'm wrong.

Rick

Interesting. If it has two sets of points, does it also have two condensers or coils? Why or why not?

ike so many questions in life, there is no simple one size fits all answer. Primarily the discussion here is about dual point, single coil, single condenser systems. It has been answered that the purpose of dual vs single was to extend dwell AND to cut down on point bounce so as to function well at higher RPM. Apparently more the latter than the former, but both are good when needed. The two sets are not on exact opposite sides of cam, but offset a few degrees from a 180 position, such that one set lags the other in opening & closing. Wired in parallel, this results in one set performing the closing of primary circuit and the other set opening the circuit. Overall result is greater dwell than either set alone. Typically, these may have ~8 degrees greater dwell than single point systems can reliably achieve. They could extend dwell even more if high RPM requirement were not present, but this requirement forces the cam design to use milder acceleration/deceleration ramps, which work to decrease dwell. This is where the dual point comes to the rescue in restoring (and actually modestly increasing ) the dwell that is lost in the high RPM cam-ramps design.
Now to the "no simple one size fits all answer". Some poster mentioned motorcycles, so I will address a few twins with which I am familiar. These have dual points, dual coils, and dual condensers. Actually two independent ignition systems....one for each cylinder. But all twins are not like this. Some have a single set of points, coil, condenser. It depends on whether they have 180 degree or 360 degree cranks, to use Honda terminology. One Honda 450 twin can be found with dual igns (180) and the same 450 Honda with single ign system (360). Same bike, same basic engine with different crank designs & igns. I wasn't in Honda engineering, so don't ask me why???!!!

 

[Hobo,NC]

Next thang you know folks will take most of what you stated and etch it in stone... I hope you understand and what you left out is if 7KV is all yer coil will out put you are in deep do-do... I doubt it will even start cold much less accelerate...

 

[gwstang]

Now to the "no simple one size fits all answer". Some poster mentioned motorcycles, so I will address a few twins with which I am familiar. These have dual points, dual coils, and dual condensers. Actually two independent ignition systems....one for each cylinder. But all twins are not like this. Some have a single set of points, coil, condenser. It depends on whether they have 180 degree or 360 degree cranks, to use Honda terminology. One Honda 450 twin can be found with dual igns (180) and the same 450 Honda with single ign system (360). Same bike, same basic engine with different crank designs & igns. I wasn't in Honda engineering, so don't ask me why???!!!

The above mentioned Honda was a '77 550F 4 cylinder with dual points and it would scoot for (what now a days anyway since they seems to be upwards of 1500-2000 sizes) was a relatively small mc engine. Thanks for the great picture of how those things work. I have wondered about that since way back in about '77.