Seem to remember this type of thing with the 508 ic way back when.
Someone Always wants it higher revs.
One option that you might be able to apply is mount the magnet on the back of the hall effect and use a slotted metal disc or similar.
Ain't that the truth. My little CDI Sparky is capable of doing 50,000 RPM on a single cylinder but, then again that's using a 12 volt battery. I have thought about the window wheel.
Instead of thinking in terms of RPM, think in sparks per minute. For guys like myself who build multi cylinder engines sparks per minute is easy to deal with. For a v8 or a 9 cylinder radial to run at a decent Rpm the sparks per minute may need to be in the 20 to 30 thousand range.
This is where the CDI ignition is nice. It can fire at a higher RPM than a standard inductive ignition because the CDI can be charging all the time. As I mentioned above my Sparky ignition can do 50,000 RPM on a single cylinder but, yah divide that by 8 for an 8 cylinder and now it's limited to 6K-7K range. It can go higher with a different coil, lower primary voltage, or higher battery voltage. The 50,000 RPM is with the custom coils I had made. Problem with CDI ignitions is with the coils they use which, usually stop working once the primary voltage goes below 120 volts. My Sparky starts off at 1,000-1,100 volts primary.
Slightly off topic. But can an ignition circuit be judged by the ability of a spark to jump a certain gap in air. So for example if a spark jumps 10mm in air is it likely to be OK under compression say 6 or 7 to 1
No, because of how transformers/coils (same thing) work, one also has to consider the amount of sparkplug gap and the fuel being used. For example; magnetos are considered low voltage high current and are used almost exclusively with LL100/110 8:1 compression aircraft engines which are also centrifugal supercharged, think DC3 radials. At 18 inches of manifold pressure that equates to 17:1 compression at higher RPM and they still work fine. The standard inductive (points) is considered medium voltage medium current and we know how well they work. CDI are considered high voltage low current, you put more current in trying to charge the capacitor than you get out (the caps ESR resistance is limiting). Magnetos do not put out any voltage it's just a current generator, the voltage is created by the high resistance of the transformers primary. When it comes to inductive ignitions companies have always played around with the coil resistances and point material to get a stronger spark, like Accel and their super coils, tough on points. CDI is a similar story as inductive. So back to your original question. How the coils work is they have a high initial current flow under high starting voltage @12v for inductive and 200-1,000v for CDI. That initial high current flow causes a high voltage in the secondary but and I mean but, as soon as an arc across the plug gap happens the coil's secondary is shorted out. When this happens all the excess voltage is converted into current. You need high voltage to jump the gap but, you need current to burn the fuel. Both air and fuel are both dielectrics, so you need a spark strong enough to punch through them to cross the gap. So now the type and octane of fuel comes into play. Low octane fuels are easier to punch through.
Anyway using that compression range and regular fuel say 87 octane you should be fine with a 10mm spark. In fact a lot of engines using that much compression get away with just a 10Kv spark.
Cheers
Ray
P.S. I have some charts, research papers, and thesis papers on spark, spark voltage and combustion if your interested.
