new high RPM Jaguar CDI

[Deleted member 12676]

For decades there have been two types of Capacitive Discharge Ignitions (CDI's) for two stroke engines; analog and digital. Their purpose is to cause the ignition spark to happen at a certain amount of crankshaft degrees before the zero degrees of the pistons top most position in the cylinder. Above 7200 (more or less) rotations per minute (RPM) of the crankshaft the best engine performance has been with digital CDI's because an analog CDI retards the ignition too much. This page reveals a new type of analog CDI which has an ignition timing curve (see graph below) in between that of a digital CDI and an analog CDI which gives enough ignition advance at high RPM for better performance and lets the engine achieve higher rotational speeds. It uses only the voltage waveform from the stator coil as a timing reference, as opposed to those that use a voltage input separate from the stator coil.

Digital CDI’s can be programmed by the manufacturer for any ignition curve desired but the curve shown in the graph above is from a Suzuki RM 250cc at medium throttle position. It is a good example of what curve a digital CDI normally has. The analog CDI curve above is from a Kawasaki KDX 200cc which limits the engine speed to 9000 RPM. Below is another example showing how an analog CDI can only somewhat match a digital CDI between 5000 and 8000 RPM:

DESCRIPTION
This modified analog CDI has two main features;
1) It allows the owner the selection of different input resistance which affects the whole timing curve, and selection of different capacitance which affects the timing curve above 3500 RPM.
2) It causes the ignition to happen earlier at high engine RPM (more than 7200 RPM) than a standard analog CDI. It does this by activating a relay above 6000 RPM which changes the RC value in the retardation circuit to retard the timing less than it normally would.

Higher input resistance causes more advancement of the whole ignition curve, and higher capacitance causes more retardation of the ignition curve above 3500 (with the greatest change at higher RPM). This allows the owner the ability to adjust the ignition curve to be more correct for different engines and expansion chambers. Selection of different resistance and capacitance is done by moving the levers of the switches that are soldered to the circuit board. Input resistances available are 15 ohms, 16 ohms, and 17 ohms by different lever positions at switch labeled "SW1". Circuit capacitances available are 4.7 microfarad, 5.2 microfarad, and 5.7 microfarad by different lever positions at switch labeled SW2.
Here is the graph showing the changes in standard ignition curves for the different input resistances:

Here is the graph showing the changes in standard ignition curves for different circuit capacitances.

Why is 7000 RPM the engine speed above which the ignition timing needs to retard less? From 3500 to 7000 the fuel/air mixture gets mixed better as RPM increases due to turbulence. The more atomized the fuel droplets are due to turbulent mixing the quicker the whole mixture can burn. A slow burning mixture needs to be ignited earler (more advanced timing) so that the peak cylinder pressure can happen around 15 degrees after top dead center. A quick burning mixture needs to be ignited later. Above 7000 RPM fuel atomization improves very little with more RPM so the ignition curve needs to almost flatten out above 7000 RPM.
Is this detrimental at all to engines not ported for high RPM? No. You can buy this CDI if you think you may be modifying yours later to rev higher than 8000 RPM. But the old version is still available from JNMotors at a lower cost for those who doubt they will modify to that extreme.
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These will be available in a couple of weeks directly from me here in South America. Message me if you want one. Cost is $50 and you need a good high voltage coil to go with it.

 

[a.graham52]

What kind of difference will there be compared to the jag coil and cdi I bought from jnmotors I bought 3 months ago?

 

[Fabian]

My maximum engine speed is 5,000 rpm and i typically ride using 3,500 to 3,800 rpm, but lug the engine as low as 2,200 rpm, upon which it detonates on 98 octane fuel, using a medium compression billet cylinder head when the engine is running red hot (with next to no airflow over the engine hauling heavy loads), but makes the most power when using the most advanced ignition curve at 4,800 rpm with acceptable cylinder head temperature.

For my application i need to be able to retard the ignition curve more (than the lowest ignition curve setting on the Jaguar CDI) in the lower rev range, yet be able to keep the highest ignition curve in the upper rev range, which i cannot do with the current jaguar CDI setup.

Having said that i don't regularly lug the engine at very low rpm and the benefits of the Jaguar CDI are proven from my experience using it, however it would be nice to have greater controllability over the ignition curve than preset ignition curve settings.

Ideally i want to have a controller attached to the handlebars, allowing me to adjust the ignition timing on the fly to suit different riding conditions; maybe something like a graphic equaliser on an older stereo system; having sliders to control ignition timing for idle, 2,300 rpm, 3,000 rpm, 3,700 rpm, 4,400 rpm, 5,100 rpm.

 

[Deleted member 12676]

For engines that rev less than 8000 RPM there is no difference between the two CDIs. Stock top RPM is 5500.

Fabian, just solder wires to the jumpers and to miniature switches. You can mount the switches in a plastic project box and connect it to your handlebars. like this:

 

[Fabian]

Great, now show me a circuit diagram how to incorporate 6 slider switches or rotary potentiometers for idle, 2,300 rpm, 3,000 rpm, 3,700 rpm, 4,400 rpm, 5,100 rpm.

 

[Deleted member 12676]

Just connect one switch to each jumper and do your own testing to see which jumper combinations are best for each speed range. Then tape onto the switch box the winning combinations. Since this is slightly off topic please message me to continue this conversation if you want to.

 

[Huffydavidson]

My "HD LIGHTENING CDI" WILL CRUSE THIS WANTA BE RACING CDI.

 

[Deleted member 12676]

It is finally ready (click here) and the difference between the CDI with and without the additional circuitry is that without an expansion chamber it can allow as much as 900 top RPM more. Expansion chambers have a set powerband with a limit of top RPM. Changing the header length changes the top RPM. I like to test setups with the standard exhaust pipe to find its top RPM and then put on my torque pipe and adjust the header length till it matches the same top RPM.
The fact that it revs out farther confirms the correctness of the timing curve of digital CDIs. Analog CDIs limit the max RPM by excessive timing retard at top RPM. This design makes an analog CDI more like a digital CDI.

 

[IbedaYank]

no pics... no video... no nothing but text on a screen to back up claims... no printouts of dyno runs or detailed information on his test motor setups


where is the PROOF??

 

[Deleted member 12676]

good question

as soon as I receive my new timing light I will make a video showing the timing difference at high RPM

seeing as how it approximates something which is considered "standard" with racing two stroke engines I dont see the point in asking for dyno printouts. No one in the two stroke racing world doubts that the timing curve needs to back off at high RPM. If you doubt and need "proof" via dyno printouts that just shows how uninformed you are.