Coil Location
Neal is right advising caution without concrete evidence. I’ve had the Indigo electronic ignition, with the Crane Cams/FAST XR700 control unit, since 2000 (newly installed hour meter - 0 hours). I had 3 coil failures in 12 years (1340 engine hours). The three failed coils had no ballast resistor. After the last failure in 2012 I added a new Indigo 3.3 ohm coil, also mounted on the engine, with the Indigo 1.5 ohm external ballast resistor. I added the ballast resistor based on this forum’s, especially Neal’s, work. In this configuration the coil temperature after 1-1/2 hours at only 1100RPM was 187 deg F.
In 2015 (1370 engine hrs) I moved the coil and ballast resistor off the engine to a nearby bulkhead, with a small cooling fan. Coil temps now were in the 102 deg F area.
In May 2018 (1700 engine hours) I changed the XR700 control unit to the XR3000, and changed the coil to a NAPA 1.4 ohm one with NO ballast resistor and no cooling fan, both still mounted off-engine.
Also in 2018, I mounted an old Bosch 3.6 ohm coil on the engine, not electrically connected up, to measure the coil temperature due principally to conduction and convection from the engine’s proximity. A test was started with a block and coil(s) temperature of 71 deg F. After running 1 hour at 1400 RPM in gear, the off-engine active coil was 107 deg F (36 deg F rise). The engine-mounted inactive coil was 114 deg F (43 deg F rise). Block temperature where the Bosch coil was mounted was 180 deg F.
My conclusion is that, for this test, block mounting alone results in a coil temperature rise of 43 deg F.
Neal is right advising caution without concrete evidence. I’ve had the Indigo electronic ignition, with the Crane Cams/FAST XR700 control unit, since 2000 (newly installed hour meter - 0 hours). I had 3 coil failures in 12 years (1340 engine hours). The three failed coils had no ballast resistor. After the last failure in 2012 I added a new Indigo 3.3 ohm coil, also mounted on the engine, with the Indigo 1.5 ohm external ballast resistor. I added the ballast resistor based on this forum’s, especially Neal’s, work. In this configuration the coil temperature after 1-1/2 hours at only 1100RPM was 187 deg F.
In 2015 (1370 engine hrs) I moved the coil and ballast resistor off the engine to a nearby bulkhead, with a small cooling fan. Coil temps now were in the 102 deg F area.
In May 2018 (1700 engine hours) I changed the XR700 control unit to the XR3000, and changed the coil to a NAPA 1.4 ohm one with NO ballast resistor and no cooling fan, both still mounted off-engine.
Also in 2018, I mounted an old Bosch 3.6 ohm coil on the engine, not electrically connected up, to measure the coil temperature due principally to conduction and convection from the engine’s proximity. A test was started with a block and coil(s) temperature of 71 deg F. After running 1 hour at 1400 RPM in gear, the off-engine active coil was 107 deg F (36 deg F rise). The engine-mounted inactive coil was 114 deg F (43 deg F rise). Block temperature where the Bosch coil was mounted was 180 deg F.
My conclusion is that, for this test, block mounting alone results in a coil temperature rise of 43 deg F.
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