ermmm...any info to back this claim up?
BCPR6ES = Standard electrode
BCPR6E = V-groove electrode. NGK claims Improved ignitability due to sparking at periphery of the electrode.
250kw, I would go 7's. As mentioned on NGK website:
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Example Take a Holden engine which as standard uses a BPR 5ES spark plug. (The heat range for this spark plug is 5, please refer to our part number identification for further information) If a customer were to install a turbocharger, intercooler and exhaust system to this vehicle, it would be suggested to start with a spark plug with a 7 heat range (BPR 7ES) to be on the safe side. The customer would then need to perform some road testing,
* firstly applying half throttle
* then inspecting the plugs,
* ¾ throttle then again inspecting the plugs
* and eventually full throttle.
At any stage of inspection if the plugs upon removal are very clean and white along the insulator nose this would indicate that the spark plugs are reaching their upper temperature threshold and as such obviously may not withstanding the temperature at full throttle. Fouling a set of spark plugs is very cheap compared to the cost of the engine modifications performed and insignificant compared to the amount of research and design that goes into producing the engine by a vehicle manufacturer.
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