MSD/GM HEI Coils
When forced induction is applied to the combustion chamber of an engine, the resistance across the gap of a spark plug increases. The greater the amount of boost, the greater the resistance. There comes a point where the factory coils cannot produce a large enough voltage across the gap of the plugs at the right time to initiate a spark. A couple solutions to this include narrowing the gap of the plugs (from the factory spec of 0.044" to about 0.030") or modify the ignition system to control stronger coils, or at least a combination of each. Thanks to several folks on the MiataPower list and in the miata.net forums, we were able to figure out how to get stronger coils running in a miata application.
The links below show the procedures for this modification on miatas I've worked with.
1991 Miata w/ Link ECU: MSD/GM coil packs
1994 Miata w/ Link ECU: MSD/GM coil packs
Here are is the parts list thanks to those that contributed to this modification:
|Part||Number required||Manufacturer||Part Number||Source||Approx price (US$)||Notes|
|Coil interface module||2||MSD||8870||www.summitracing.com||$27|
|Waterproof case||1||Hammond Mfg.||1590WDD||www.digikey.com||$19|
|8.5mm Spark plug wires||1 set||Magnacor||"Vishnu Performance spec wires"||
Call the directly at 248-471-9505
Autozone, Advance, or Pep Boys
||$4 per 30 foot roll|
|MOSFET N-channel transistor||1||Radio Shack||276-2072||Radio Shack||$2|
|1/4 watt 470ohm resistor||1||Radio Shack||Radio Shack||<$1|