79 gs750e with dyna s ignition, 3ohm or 5ohm coils?

[Northern Mike]

So I had installed 3 ohm dyna coils 2 years ago but only did a few short rides with it. Last weekend, 300km from home, hot day, one of the coils failed. Its been a while since I really worked on this motor and I could have sworn it was still points on it. Realizing I should have put 5 ohms with points, i figured that was my failure (hot day, long runt time at 110kmph) .
Realizing now I have a Dyna S ignition, I'm assuming 5 ohms is the wrong coils.
What resistance coils should I be running with a dyna s ignition?

[tom203]

If you got the dyna ignition , use the dyna 3 ohm coils... if you have stock points setup, best to stick with 5 ohm stock ignition coils.

Are you sure one of your dyna ignition coils failed, and not the dyna module? It's real hot down there on crankshaft end and hot days add to it.

[Northern Mike]

If you got the dyna ignition , use the dyna 3 ohm coils... if you have stock points setup, best to stick with 5 ohm stock ignition coils.

Are you sure one of your dyna ignition coils failed, and not the dyna module? It's real hot down there on crankshaft end and hot days add to it.

First Not side of the road test i did when i got the bike off the trailer was swap the wiring between the two coils and the issue remained with the coil.

[Steve]

Using 5Ω coils with the Dyna will not hurt anything.

A coil with lower resistance will allow more current through it. More current means a stronger magnetic field, which will give a stronger spark. Points are not able to handle the increased current, but the transistors in the Dyna system (and the stock "ignitor" on newer bikes) can handle it.

Using 5Ω coils with a Dyna S will give the same-strength spark as original. It is adequate, but could be better.

.

[Northern Mike]

Using 5Ω coils with the Dyna will not hurt anything.

A coil with lower resistance will allow more current through it. More current means a stronger magnetic field, which will give a stronger spark. Points are not able to handle the increased current, but the transistors in the Dyna system (and the stock "ignitor" on newer bikes) can handle it.

Using 5Ω coils with a Dyna S will give the same-strength spark as original. It is adequate, but could be better.

.

That is what I was thinking. I have not installed to coils yet as they are still in shipping. Might return themcand get 3 ohm again.
The kicker is that the 3 ohm on points would hsve explained the failure of the just over a year old set of dyna 3 ohm coils.
Need to figure out why they failed. Getting expensive changing coils on this bike

[Northern Mike]

While looking for more info on the dyna S system and their coils, I found this thread on a Honda CB forum which sounds interesting and possibly applicable to our bikes.
Thoughts?

http://forums.sohc4.net/index.php/to...html#msg951844

The answer IS definitive, IF you care to pay attention to physics and math.
The points draw power through the coils during 195 degrees of crankshaft rotation.
195/360 (degrees of rotation) = .54 or 54% coil on time for EACH coil/points set.

The DC resistance of ONE coil primary and the voltage applied to it determines the current/power draw of the coil.
12.6V / 5 ohms = 2.52 amps. And 2.52 amps x 12.6V = 31.72 Watts There are TWO coils for a maximum consumption of 63.504 Watts. However, the points only allow each coil to be on during 54% of crank rotation.
So, 54% of 63.504 watts = 34.29 Watts power consumption. (<-- STOCK IGNITION SYSTEM)


The Dyna-S dwell time (coil ON time) is 315 degrees of crank rotation (using Hondaman's ignition analysis).
315/360 (degrees of rotation) = 0.876 or 88% coil on time for EACH trigger switch.

Still using 5 ohm coils, the power draw increases just because they are on for a longer duration of time.
There are 2 coils driven by the battery. While the coils draw the same power as with points when they are closed, the current power draw time for the electronic switch is increased from 34.29 Watts to 55.88 watts power consumption, just by using the Dyna-S.

Now add 3 ohm coils And the Dyna-S
12.6V / 3 ohms = 4.2 amps. And 4.2 amps x 12.6V = 52.92 Watts There are TWO coils for a maximum consumption of 105.84 Watts. The Dyna-S allows each coil to be on during 88% of crank rotation.
So, 88% of 105.84 watts = 93.14 Watts power consumption. (<-- DYNA-S and 3 ohm coils)

So, the "high performance" changeover sucks far more than double the power as the stock system. (more about this later)

Can YOUR charging system still keep up the normal bike loads AND an increase of consumed power? This depends on your model bike and how you ride it.
You want your lights on? Then most of the SOHC4s with stock ignition draw about 10-11 amps, when lights and key switch are on. That's about 120-140 Watts.
The alternator's outputs vary by model and the RPM they are spun at. The 400, for example, is rated at 156 watts @ 5000 RPM. Note that idle RPM is about 1/3 of maximum output. If you add an additional 60 watt ignition system load to the normal stock load you will have a 180-200 watt load on a system capable restoring 156 watts max. You better hope that your alternator was made to perform better than minimum performance specs at the factory AND that you will never run the engine below 5000 RPM, or your battery will run flat in under an hour, and you have a wonderful push toy.

But, what does the "high performance" ignition system do for you in exchange for short battery life?
The spark plugs fire with energy stored in the coils when the points/ electronic switch while is turned off. This allows the energy field created by the coils to collapse. The collapse continues until there is enough voltage the create a low resistance plasma channel between the gap electrodes. This is when current flows through the system and spark occurs. Notice that while there must be enough energy in the coil for this to occur, that actual voltage need for the event is determined by the spark gap (the gaseous conditions between the gap), NOT the coil max capability. This means that peak potential voltage that the coil is capable of producing does NOT translate to higher spark voltage. This is only what salesmen and "believers" want you to assume in order to separate money from you wallet. ALL the testimonials from "believers and "marks" that have bought the lie mean nothing in the real world of true physical behavior.

When do you "NEED" higher spark potential?
1 - Change the plasma channel conditions between the spark electrodes. Higher pressures require higher voltage to create the channel (I.E higher compression ratio.)
2- Increase the spark GAP between the electrodes. A larger gap require more voltage to form the plasma channel.
3- extend the useful life of spark plugs. As spark electrodes wear, they actually need higher voltages to form the plasma channel.

But, does the extra power of the system add to rear wheel HP on the road? No, this is preposterous. Even if you did add 60 watts consumption to the ignition system and delivered it to the combustion chamber. 60 watts = 0.080461325 HP. And remember half is that total increase in power consumption is wasted, sparking between exhaust and intake stroke. It CAN be logically argued that other engine changes that (in turn) require higher spark voltages will increase the rear wheel power. But, ignition power alone does not not, can not.

The Dyna-S does provide a consistency of spark (timing and duration), that the points trigger system can't maintain during extended use. This is due to the high currents during make and break of the point contacts, causing overheating and distorting the contacts themselves. These effects are cumulative. Devices that reduce the current flowing through the points greatly extends their stability and reliability. It is too bad the Dyna-S doesn't mimic the stock points dwell/ points cam time durations. If it did, it would be a total win and worth more of the inflated price they ask for a short sighted design. IMO

For street use conditions 5 ohm coils are most appropriate.
For modified engines, racing applications, 3 ohm coils may be a better choice (other factors to be considered), IF your charging system is up to the task or you don't have far to push the bike back to an external battery charger.

Maybe someone will actually read this?

Cheers