About the HEC coil
HEC stands for High Energy Coil. Bosch makes it in several versions, and Haltech sells it as part number HT-020110. The three-digit model number doesn't change the coil's electrical specs. It only changes the connector type and orientation and the style of the high-tension post. For example, the HEC726 uses a male post shaped like a spark plug top. Bosch describes the coil as intended for generic and custom applications, so there's no "right" car for it.
Bosch also redesigned the housing some years ago, so an older HEC715 can look quite different from a new one while doing the same job.
You need an external igniter
The HEC has no igniter built in. The ECU's ignition outputs can't switch coil current directly, so an igniter module sits between them. This coil can pull close to 20A at peak charge, which is far more than a typical coil, so pick an igniter built for heavy current. Haltech's HPI range is the recommended option: the HPI4, HPI6 or HPI8 depending on how many coils you run. If you're unsure where the switching happens in your system, see internal igniter or not.
ECU settings
| Setting | Value with an HPI igniter | Why |
|---|---|---|
| Ignition Mode | Depends on your installation | Wasted spark, direct fire or distributor, set to match how the coils are laid out |
| Ignition Edge | Falling | Matches how the HPI igniter expects to be triggered |
| Ignition Dwell Mode | Constant Charge | Lets you control charge time directly from the dwell table |
Dwell: the part that matters most
The HEC's limit is heat. It keeps storing more energy with longer charge times and doesn't reach full saturation until the dwell is quite long. But holding it at full charge all the time makes it run hot, and a hot coil doesn't live long. The fix is to use full dwell only when the engine actually needs full spark energy.
The way to do that is to map the dwell table against battery voltage and engine load:
- Normal running voltage, off boost: keep dwell relatively short. The engine doesn't need a huge spark at light load.
- As boost builds: ramp dwell up gradually. Higher cylinder pressure takes more energy to jump the plug gap.
- High boost: reach full dwell. Haltech's example peaks at roughly 30 psi (200 kPa), where the coil gets full dwell and full spark energy. Set your own peak point to suit how much boost your engine runs.
- Low voltage, like cranking: add dwell so the coil still charges fully when battery voltage sags, which helps starting.
This gives you a strong spark where you need it and a coil that isn't sitting at full heat while you cruise. Haltech has an example dwell table for this coil. Need it? Ask us and we'll send it over with advice for your build.
Start conservative, then only add dwell where logs or the dyno show misfire under load. After a hard session, feel the coils. If they're too hot to touch comfortably, you're asking too much of them at cruise.
Power supply
At close to 20A each at peak, a set of HEC coils puts real demand on the power feed. On a high-RPM, high-boost engine, one ordinary 30A relay feeding every coil can run out of capacity. It has happened on rotary builds spinning past 10,000 RPM with lots of boost. In that case, give each pair of coils its own fuse and relay.
The wiring matters just as much. If the wires are too thin for the current, voltage drops at the coil and spark energy drops with it, no matter what the dwell table says. Size the power feed for the peak current, not the average.
Troubleshooting
| Symptom | Usually |
|---|---|
| Misfire under high boost only | Not enough dwell at high load, voltage drop in the power feed, or plug gap too wide |
| Coils running very hot | Dwell too long at light load |
| Hard starting | No extra dwell at low battery voltage |
| Misfire that gets worse at high RPM | Relay or wiring can't supply the current; split the power feed |
HEC coil FAQ
Is the HEC a good choice for a rotary?
It's a common choice on high-boost rotaries, where strong spark energy is needed. If you're setting one up, our notes on rotor phasing and tuning rotary engines are worth reading.
Can I use a different igniter?
Only one that can reliably handle the HEC's peak current. Underrated igniters overheat or limit the spark. If you'd rather use a coil with a built-in igniter, look at the IGN-1A coils.
