dyna coils question

I ordered a set of dyna coils 3ohms for my gpz750 engine

the sender sent 5ohms coils,

question is can i use these 5ohms coils with my engine which has standard ignition pickups and igniter?

if not could I use them on my Z1900 with std points setup?

My understanding is you can use greater than 3 ohms but not less than. Something about possible overheating of the coils(could be wrong).

No danger going up in resistance, only down. I believe the stock coils for yours are 4 Ohms and Z1 sells OEM replacements if you want 4 Ohm coils. A 5 Ohm coil should work fine.

OK, I'll give them a go.
cheers

As others mentioned, as long as they are over 3 ohms (within reason) you should be ok...

Question, why not send them back and get what you ordered?
NOTE: Unless you got them off e-bay or something as such...

Granted, the image is for the KZ900... But look at the last paragraph.



OMR

Points coils were about 4 ohms. Higher is safe, but may give weaker spark. 3 ohms will work but will shorten the life of the points somewhat. Dwell is about 180 degrees with points.

Kaw factory electronic-ignition coils were about 2.5 ohms. 3 ohms works well with it. Any higher and you start to get a weaker spark. This is because the dwell is reduced to only about 120 degrees with the Kaw factory electronic-ignition (which allows useage of hotter coils).

Dyna S ignition recommends 3 ohms or higher coils. The dwell on the Dyna S is nearly 360 degrees, so new 5 ohm coils should work fine. 3 ohms may make more spark, but should only really make a difference at higher RPMs on a good, well-jetted motor.

The resistance you mentioned here is of course the primary winding. What about the resistance of the secondary winding? Isn't the strength of the sparks the results of the difference between the windings?

eaglecrash2 wrote:

The resistance you mentioned here is of course the primary winding. What about the resistance of the secondary winding? Isn't the strength of the sparks the results of the difference between the windings?

You are correct, the measurments are only of the primary side resistance, but coils are similar enough for motorcycles that we can take some liberties with judging them based on primary resistance. Typically they are, if I recall, generally in the 100 to 1 ratio for the windings. Also, the higher the resistnace of the primaries, the higher their inductance is, very roughly speaking. So we can assume higher resistance coils will generally also require longer dwell to fully charge.

Because the current on the secondary side is low, we don't worry too much about the resistance there. That's why resistor plugs, caps, or wires can be used without decreasing spark by too much. We measure the secondary resistance just to look for defects from one coil to another, but I don't know of a correlation between performance and secondary resistance. (There may be one, but I've never heard much discussion of it.)

eaglecrash2 wrote:

The resistance you mentioned here is of course the primary winding. What about the resistance of the secondary winding? Isn't the strength of the sparks the results of the difference between the windings?

NO, it's actually a result of how much energy is stored in the primary winding and then dumped out of the secondary when the primary winding "breaks" when the points open. The design topology is called "flyback" in the parlance of magnetic converter design. The basic principle is the primary winding stores energy while current flows in the primary and then that energy dumps from the secondary when the primary opens. The primary and secondary couple because they are a transformer, he secondary voltage is stepped up greatly by the transformer turns ratio. The actual energy delivered is dependent on an assortment of variables.