Shielding & EMI Control (Shielded Only)
Why Ignition Wires Radiate EMI
- Spark plug wires carry very high voltage pulses (20,000–50,000 V) with extremely fast rise times.
- Those sharp pulses act like little radio transmitters, spraying electromagnetic interference (EMI) into the engine bay.
- Unshielded wires can cause:
• Radio static (especially AM).
• Sensor glitches or dropouts in EFI or aftermarket gauges.
• Crosstalk between adjacent wires (#5/#7 misfire issues in V8s).
How the Shield Works
- Shielded IndestructaWires use a braided copper shield wrapped around the conductor under the outer sheath.
- This shield captures radiated noise and routes it harmlessly into a short Tefzel ground lead at the distributor end.
- Once the noise is grounded, it’s no longer radiated EMI — just low-level current safely drained into the chassis.
Measured Effectiveness
- The shield reduces ignition noise by 20–60 dB depending on frequency.
- That’s equivalent to 10× to 1,000× less radiated interference compared to unshielded wires.
- Effectiveness is strongest in the AM/VHF frequency bands, which are the most common trouble spots for ignition noise.
Real-World Benefits
- Noticeably cleaner idle and smoother tach readings.
- More stable signals for wideband O₂, MAP, crank, and other sensors.
- Radios and communication systems remain usable even with a hot ignition.
In Plain English
Shielded IndestructaWires don’t just carry spark — they stop your wires from acting like antennas. The copper braid blocks ignition noise so your engine runs smoother, your electronics stay clean, and your spark stays strong.
Analogy
Think of unshielded wires like a leaky garden hose spraying water everywhere. The shield is the outer sleeve that catches those sprays and directs them into a drainpipe (the ground lead). Instead of making a mess in your engine bay electronics, the “spray” is captured and routed away safely.