Spark Plugs - standard heat range Unipart GSP6662 Champion RC9YCC NGK BCPR6ES Bosch FR7DC Spark Plugs - cooler heat range Unipart GSP6652 Champion RC7YCC NGK BCPR7ES Bosch FR6DC
The regulations. I only know this because i looked it up recently. I would use BCPR6ES. I use these on my proto engine but the platinum tiped version. But i guess they are banned in S1600!
Andy, the Regs say specifically and have for years and years, ... 7ES they have never said ...7ES -11. Therefore your question should never have arisen!!
We allowed the cooler 7 plugs about 14 years (or more) ago.
Correct Jamie, Steve had sort of covered that by copying and pasting the regs straight away .....
I'm pretty sure we included the two heat ranges of plugs soon after the introduction of the K series engine at the suggestion of Steve Wood of Longbridge - so probably 1997 or 98!!