The spark plug gap is the distance the spark jumps across the electrode. Too small and the spark is weak; too large and the coil may misfire. This chart gives typical ranges — your engine has one correct spec.
| Application | Typical gap | Notes |
|---|---|---|
| Older points ignition | 0.025 – 0.035 in | Weaker spark energy |
| Standard modern engine | 0.040 – 0.054 in | Electronic ignition, common factory range |
| Turbo / supercharged | 0.028 – 0.035 in | Tighter gap resists blow-out under boost |
| Nitrous / high boost | 0.020 – 0.028 in | Tightest, for dense cylinder charge |
The manufacturer spec always wins. Find it in the manual or under the hood, and set it with a wire-style gauge — tapered feeler gauges can misread the round gap.
Pre-gapped plugs are not always at your engine spec; check every plug before installing.