Topic: dyna/electric

[j-conn]

Ok so I have been chewing on bits and peices and letting things settle in. Ive just read a ton on carbs in the last week or so. Knew what they did but not really how or what kinds there were. Now i do  (except the cr's... what exactly makes them 'performance'. weight/efficiency?)

Next thing is electrical. could someone shed alittle light on some "theory" i guess you could say behind these sohc electrical systems. I have been trying to figure out what a 'dyna' does actually and im alittle confuse. i see there are dyna 'coil' but i feel like ive also seen boards of some kind that you can program. what do these replace (if anything). and if they do what does the exsisting system do and how.

i guess starting from the battery to the spark is what i am trying to understand. how does the engine 'know' to speed up the firing of the spark? what is communicating with what in that regard. my first thought was that there must be a seperate arm rocking on the cam that controls the spark but i am still new to alot of this.

i know the theory of how a cumbustion engine works but i guess im finding that theory doenst mean everything 

links to exsisting threads are cool too. i know there is tons of info to be found!

[tsflstb]

Dyna makes coils, they also make ignition controllers.

You'll hear about a Dyna-S, which replaces the points with a hall effect sensor and still uses the mechanical spark advance unit.  Look under your points cover and there is a cam that turns with the engine.  It's also held by springs that change it's orientation at higher engine speeds.  That's what advances the spark

There's also the Dyna 2000 which does all that electronically.  You can program in different timing advance curves and possibly make espresso with it.

[j-conn]

ok cool...
gears in my head are starting to turn.

[Jerry Rxman Griffin aka MuthaF'er]

The stock carbs have a 28mm opening for air to enter. Basic difference, the CR's have either a 29mm or a 31mm. More air = more gas = bigger bang (if set up correctly) = $800. 29's are a good conversion for a stock to mid-level performance engine. 31's only on a more serious larger displacement engine. 

MOST dyna coils that we use are the green 3ohm vs the 5ohm (I believe) stock coils. Some even use the 2.2ohm gray coils. They are designed to throw a much hotter spark at the spark plug ensuring a better bang. Most stock coils are 30+ years old, have 30+ year old plug wires, and 30+ year old plug caps. Note the 30+ part here, good enough reason in itself to replace but may not be necessary. Potential downside is the Dynas require more electricity to throw a better spark which in turn can really tax a weak electrical system. If you don't like replacing and trying to time 2 sets of points by all means put a Dyna ignition in. Set it correctly once and forget it!!

The timing of the spark is determined by the crankshaft. The "seperate arms" are the points opening and closing with the rotation of the crank.       

[TwoTired]

Let's begin with the spark plugs.  Each electrode tip has a gap, over which a spark jumps.  The heat from this spark ignites the fair fuel mixture in the chamber, resulting in the power stroke of the 4 stoke engine.  The coils and points work together to create the spark voltage, along with a cam that turns with the crankshaft on one end of it.  When the cam is in a position that allows the points to close, energy flows through the points and the primary side of the ignition coil.  This builds a magnetic field within the coil and stores up energy from the battery.  When the crankshaft turns far enough, the cam on the crankshaft allows the points to open, which interrupts the flow electricity maintaining the magnetic field in the ignition coil, and causes the magnetic field to collapse.  A magnetic field creates lines of flux, and as these lines of flux are collapsing, the lines cross the secondary winding in the coil and induce a voltage within that coil.  The coil output voltage rises until there is enough voltage to ionize the atmosphere at the spark plug gap, turning it to plasma, which will support electrical current.  An arc is thereby created which ignites the air fuel mixture in the cylinder.
The SOHC4 uses a wasted spark system, that fires two spark plugs at a time.  Only one of these cylinders is at the beginning of its power stroke, so only one cylinder actually has an air fuel mixture to ignite.  The other cylinder's spark plug fires between the exhaust and intake stroke.  One thing to note is that the gap on both spark plugs determine the voltage required to make the spark occur.
The primary winding of the coils for our bikes were just about 5 ohms.  These make plenty of voltage to fire the spark plugs, provided the gap is maintained at stock recommendations and that the bike's electrical system maintains 12V.  A 3 or lower ohm coil on the stock bike doesn't make any more spark voltage than the stockers, although it will draw more power from the electrical system of the bike.  To gain any benefit from lower ohm coils, one or more of the following must occur:
A ) The compression pressure must increase.  The voltage required to ionize gases and form the plasma arc is affected by the gas pressure in the cylinder.
B) The spark plug gap distance must increase.  It requires more voltage to jump a larger gap.
C) The coil's supply voltage must be lower.  The lower current that the stock coils draw, make it susceptible to low voltage input conditions.  A coil multiplies it's input voltage by the turns ratio between primary and secondary.  Lower ohm coils have a higher turns ratio.  Because of this, 3 ohm coils will still fire plugs (using stock gap) with a 6V input.  If your electrical system has deteriorated so that the coils no longer get full battery voltage, 3 ohm coils may spark your bike (particularly during electric starter operation) where the stock coils will not.  (However, there is an argument that says correcting the voltage delivery to the coils is a better path to take than replacing coils.)
D) The spark plug leads require replacement.  The stock coils are molded with their leads attached.  While replacement is possible, it ain't fast or easy.

While the stock contact points system is quite robust, it does deteriorate with use.  The cam rubbing block wears, and the current flowing through the point contacts during the make/break cycles heats the surfaces causing distortion/damage.    So, they need periodic maintenance.  To avoid this infrequent maintenance, many choose the Dyna -S Unit which replaces the points and provides almost the same function.  The difference is that it leaves the coils "ON" to charge up far longer than the stock points do.  The stock points are controlled by a cam on the crankshaft.  When the open gap is set correctly. The points are closed (coils drawing power) for 195 degree of crankshaft rotation (also known as dwell time).  The rest of the crankshaft rotation time (165 degrees), the coils are NOT drawing power from the bike's electrical system.  The Dyna-S draws power unless the coils are actually firing, which is the width of the magnet it employs, which (according to Hondaman, see ref.) is 27% of what the stock coil off time is.  This means that even when using the stock 5 ohm coils, a Dyna -S system will draw more power from your bike's electrical system, and even more with 3 ohm coils installed.

Ref: http://forums.sohc4.net/index.php?topic=29545.0

Is this explanation helpful?

Cheers,