Quote:
Originally Posted by LM3929
Is there any consensus on whether or not a CDI or CDI+ box will trigger two coils?
Lorne M.
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Lorne,
I recently inquired at classic retrofit about this and this is the reply I got:
Quote:
Hi Tom,
You need two boxes. At the end of the day, this is electronics and physics. If you put 2 coils in series or parallel with a single box, you change the characteristics of the circuit. Both configurations result in only half the spark energy being presented to the flame front. This is counterproductive if the reason for going with twin plug is to gain power.
Regarding the failure of one box in a twin plug system, I don't agree with the 'severe detonation' comment. In a twin plug engine, because there are two flame fronts, the fuel 'burns' faster so there is less need for timing advance. Indeed, if you check the specification of timing for a twin plug engine it is typically 5 degrees less at full advance than a single plug engine. So, if one box or coil was to fail, the net result is that the ignition would in effect be further retarded, not advanced. Retardation of the ignition typically does not cause detonation - in fact it is used to prevent detonation in many engines. You would also notice a significant drop in power from the driver's seat so it would be immediately apparent. The only negative affect of prolonged use of an engine with retarded igntion would be an increase in cyclinder temperature, however this would take a little while and you'd have noticed the drop in power long before that.
Food for thought: Consider the latest trend for COP in a twin plug application. There is typically no warning mechanism for a coil failure in those systems and modern coil pack failure is a fairly common event if my modern car is anything to go by. Now, if one of those COP were to fail (eg. one plug in one cylinder), I very much doubt that the driver would notice. They would continue to use the car and that cylinder would heat but it probably would not be detectable in engine temperature or significant power loss. I would regarding this as a far more 'dangerous' situation for the engine compared to the traditional arrangement of two coils and two CDI units.
Best Regards,
Jonny
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So it seems, no, the CDI+ cannot be programmed to output twice the energy and split to two separate coils in parallel. This was surprising to me. I know other vendors like ashlock can modify stock cdi boxes for twin plug by installing two sets of solid state electronics in a single box. I would think classic retrofit could do something similar. I’m sure their circuitry takes up more physical space, but it seems there would be a market for this. A programmable curve in a stock looking box to plug into a locked dizzy by JB racing or similar. They recommend using MSD, but I prefer the stock look of the Bosch cdi boxes.