The HKS Super Fire Racing M40i is an ISO-type iridium spark plug with an NGK 8 equivalent heat range, built for tuned and stock performance engines. Its 0.6 mm iridium center electrode and platinum-chip outer electrode lower the required firing voltage for strong ignition under high boost or lean conditions, while the thermal edge and spark-support gap resist carbon fouling. This ISO seat fits a wide range of Japanese turbo and naturally aspirated engines (RB, SR, VG, and similar) calling for an ISO φ14 plug. Sold individually.
| Product Line | Super Fire Racing M-Series |
| Heat Range | NGK 8 equivalent |
| Seat / Type | ISO type |
| Thread | φ14 x 19 mm |
| Hex (Wrench) | 16 mm |
| Center Electrode | 0.6 mm iridium |
| Quantity | Single plug |
| Part Number | 50003-M40I-1 |
Shipping: In-stock orders placed before 3 PM EST ship the same day, and everything else ships within 24 hours. Standard, expedited, and overnight options are available at checkout. Backordered items ship as soon as we get them back in stock. Contact us for lead times. See the full Shipping Policy.
Returns: 30-day returns on new, unused items in original packaging. See the full Refund Policy.
