What does the “R” mean?
For NGK spark plugs:
- BP6ES
- B = 14 mm thread
- P = Projected insulator nose
- 6 = Heat range
- E = 19 mm thread reach
- S = Standard copper centre electrode
- BPR6ES
- Exactly the same plug except:
- R = 5 kΩ internal resistor
The resistor is there to suppress electrical interference (radio noise) and also reduces electrical spikes that can upset electronic ignition systems and modern electronic devices.
Resistor plug vs resistor cap
You only need one source of resistance in the ignition circuit.
Typical combinations are:
| Plug | Plug Cap | Total |
| BP6ES | 5kΩ resistor cap | ✔ Perfect |
| BPR6ES | Non-resistor cap | ✔ Perfect |
| BPR6ES | 5kΩ resistor cap | ✔ Also perfectly acceptable (10kΩ total) |
| BP6ES | Non-resistor cap | ✖ No suppression |
Many people think using both resistor plugs and resistor caps is wrong, but BMW, Bosch and NGK have all used systems with approximately 10kΩ total suppression. The only downside is a very slightly reduced spark energy, although on a healthy ignition system it’s usually insignificant.
Electronic ignition
If your BMW 2002 has been converted to:
- 123 Ignition
- Pertronix
- Lumenition
- Electronic Bosch distributor
then BPR6ES is generally the better choice because it helps protect the electronics from ignition noise and reduces RF interference.
BMW 2002 Tii
For the mechanical fuel-injected Tii, NGK generally recommends: BPR6ES
This is the heat range that suits the higher compression and performance of the M10 Tii engine.
Carburettor 2002s
A standard carburettor BMW 2002 (1602, 1802, 2002) normally also uses: BPR6ES
The heat range isn’t determined by whether the engine has carburettors or fuel injection—it depends on combustion chamber temperature, compression ratio and intended use.
A BPR5ES is actually a hotter plug than a BPR6ES.
You might choose a BPR5ES if:
- the engine is mainly used for short journeys,
- it tends to foul plugs,
- it’s an older engine burning a little oil.
Many owners of low-compression 2002s find a BPR5ES works well, but it isn’t the standard recommendation for every carburettor car.
Heat range
NGK numbering works opposite to some manufacturers:
- BPR5ES = Hotter
- BPR6ES = Standard
- BPR7ES = Colder (competition, sustained high-speed use)
For your BMW 2002 Tii
If your car has:
- Electronic ignition
- Mechanical Kugelfischer fuel injection
- Normal UK road use
I’d stay with NGK BPR6ES gapped to around 0.7–0.8 mm (0.028–0.032″), depending on your ignition system manufacturer’s recommendation.
The old BP6ES plugs will still work if you have non-resistor caps, but unless you’re aiming for complete factory originality, I’d continue using the BPR6ES.
One additional point that often surprises classic BMW owners: if you’re experiencing misfires after fitting resistor plugs, it’s usually a sign that the ignition system (coil, leads, cap or rotor arm) needs attention rather than a problem with the plugs themselves. A healthy M10 ignition system should fire BPR6ES plugs without any difficulty.