I figure there is enough interest on this topic to have a dedicated thread for it. Some good links to read: http://www.v4spark.com/V4-COP.htm http://www.sportdevices.com/ignition/ignition.htm http://www.dtec.net.au/Ignition Coil Dwell Calibration.htm https://spdispark.com/pages/frequently-asked-questions-dwell.html http://www.jetav8r.com/Vision/IgnitionFAQ.html There are a few reasons why you would want to do this mod. You will be replacing your old coils with newer ones (they can and do go faulty, as well as degrade with age). You eliminate the spark plug caps and high tension leads as failure points. If you have a coil on plug unit fail they are easier to replace, as you only need access to the plugs, whereas the old coils are usually bolted to the frame somewhere. Generally the new coils are lighter, so you save a small amount of weight as well. If you run an aftermarket programmable ignition unit, you open up options for using direct fire instead of wasted spark, as well as programming dwell time and ignition advance. For the record, our 4cyl 250cc grey import shiteboxes use TCI - Transistorised Coil Ignition and not CDI - Capacitor Discharge Ignition. What's the difference? Look in the links above. When selecting which coils to use, there are a few things to consider: Resistance of the standard coils vs. coil on plug units is the main concern. For example on the ZXR250C, one coil (firing two plugs) has a resistance range of 2.3-3.5 ohms on the primary side. Therefore, the primary resistance of the coil on plug unit (firing one plug) must be half of this, so 1.15-1.75 ohms is the range you would need. If you use coils with too low a resistance, you stand at risk of overheating the bike's standard wiring, damaging the coils, and damaging the TCI unit. You will not gain anything by running low impedance coils. You also have to consider the physical dimensions of the new coils. They have to be the right height, and the seal up near the connector has to match the diamater of the of the old spark plug cap. On bikes with exposed plugs like the FZR250, you don't have to worry about this. OK, so you've selected some coils and now you need to wire them up. How do you do that? With a standard TCI unit, it has to be done so to work with wasted spark. @my67xr made a nice picture so I will use it: The only thing I would change here is leaving some wire untaped from the connectors, so if you go for a dyno run it makes it easier to get the engine RPM signal off the spark lead. Will get some pictures of my conversion with the ZXR as it takes place in the next few weeks.