Suitable NGK Plugs

T

Teditor

New member
I have a 1978 Fairmont GXL XC 4.1 with Extractors, bottom stock end, an Alloy head (XD or XE not sure) ported and polished and port matched to triple 45 DCOE Sidedraft Webers, I was running NGK BP6E S Plugs (I think these were for the cast iron head and probably didn't seat properly and ran black, along with backfiring), I have just put a set of NGK BP5FS plugs in (supposedly correct), improved already, but seems confusion on what is recommended, any assistance appreciated.

Only used for street driving.
 
The first question is what fuel are you using, Premium unleaded or just unleaded? Octane rating will make a difference.
 
BP5 is about right in your application, BP6 is "colder" and would better suit if your giving it some regular "wellie". I wouldnt worry too much about it. It sounds like your running rich anyway, that needs to be sorted.
 
Thanks for the advice, the BP6E S plugs were much bigger physically, 21mm spanner as opposed to 14mm and I doubt they would have been seating correctly, the smaller ones have a taper while the bigger ones have a flat washer, I don't recall the story regarding original plug choice.
 
Teditor said:
Thanks for the advice, the BP6E S plugs were much bigger physically, 21mm spanner as opposed to 14mm and I doubt they would have been seating correctly, the smaller ones have a taper while the bigger ones have a flat washer, I don't recall the story regarding original plug choice.
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Iron heads are taper seat, alloy are washer seat, all 14mm threads, washer seat is 21mm, if your got small hex on taper seat they sound like Holden v8 plugs, BP is projecting core , B is non projecting, 6 is heat range.
 
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