Spark Plugs
NGK R5671A-8 – Why Are There Two Versions with the Same Name?
Many customers are confused when they see two NGK R5671A-8 spark plugs with different stock numbers – 4554 and 2660 – and wonder why the price difference is so large. Here's a clear comparison to help you understand the difference.
| Feature | NGK 4554 | NGK 2660 |
|---|---|---|
| Stock Number | 4554 | 2660 |
| Resistor | No | Yes |
| Application | Race engines, high-performance builds | Lawnmowers, mopeds, general use |
| Price (USD) | ~6.50–9.75 | ~2.50–3.00 |
| Spark Strength | Slightly stronger | Slightly dampened |
| Electrical Noise | Possible | Reduced |
Summary:
If your engine uses modern electronics (ECU, CAN bus, data logging), go with 2660.
If you're running a purely mechanical race engine, 4554 may be the better choice – even if it costs more.
NGK R5671A and R5672A Heat Range Chart
| Model | Heat Range | Reach | Application |
|---|---|---|---|
| R5671A-7 | 7 | 19 mm | Street/strip, lightly tuned engines |
| R5671A-8 | 8 | 19 mm | General racing, turbo/high compression |
| R5671A-9 | 9 | 19 mm | Heavy racing, methanol, high heat load |
| R5671A-10 | 10 | 19 mm | Nitrous, forced induction, 400+ hp |
| R5671A-11 | 11 | 19 mm | Extreme racing, drag, methanol + additives |
| R5672A-7 | 7 | 25 mm | Street/strip, deep plug wells |
| R5672A-8 | 8 | 25 mm | Turbo/high compression, deep combustion chamber |
| R5672A-9 | 9 | 25 mm | Heavy racing, methanol, deep plug seat |
| R5672A-10 | 10 | 25 mm | Nitrous, forced induction, specialty heads |
| R5672A-11 | 11 | 25 mm | Extreme racing, drag, deep combustion chamber |
Tip:
Only use the R5672A series if your cylinder head requires a 25 mm reach.
Using the wrong reach can cause mechanical interference or poor combustion positioning.
We hope this comparison clears up the confusion. If you need help choosing the right plug for your engine, feel free to contact us – we’re happy to help!
Did You Know? Every Heat Range Has Multiple Versions
While this article focuses on the R5671A-8 plug, it's important to note that every heat range in the R5671A and R5672A series (7 through 11) also comes in multiple versions. These include:
- Resistor vs. Non-Resistor: Some plugs include an internal resistor to reduce electrical noise, others do not.
- Different Stock Numbers: Even if the plug number is the same (e.g. R5671A-9), the stock number determines the internal configuration.
- Price Differences: Non-resistor race plugs are often more expensive due to limited production and specialized use.
Tip:
Always check the full part number and stock number when ordering NGK racing plugs.
Two plugs with the same name may behave very differently in your engine.