found this in forum archives… (since you’ve had a lot of looks but no replies…) This from 2013…posts.
Hello Folks,
I am working on a V-12 that has NKG BP5ES plugs. It is running rough and the plugs look OK but thought I would replace them as a matter of course. The engine has 90K miles. Should I stick with NKG or is there another brand that might do better?
Many thanks
Reply from Dick Maury
In reply to a message from Weston Keyes sent Sat 23 Aug 2008:
Although you might be able to make the car run OK with the NGK (Nicks add: BP5ES hotter or BP6ES colder)
plugs, Jaguar calls for Champion N9YC plugs for the V12 XKE. I have
always had good luck with them. I have had running problems on cars
in the past and changing to Champion plugs have cured the problem.
Why would anyone not want to run the plug that the manufacturer
recommends, especially when it is a quality plug?–
Dick Maury , Rebuild Dept., Coventry West, Inc.
Lithonia, GA, United States
Dick went on to say gap at .025, in this: The point gap
is .015 for the Lucas single point distributor. This is for all
years of the XKE that use it and has not changed. The Petronix is a
switching device. It is not a multi spark like MSD, nor a
Capacitive discharge system nor a HEI system as on GM cars and
later model Jaguars. That said, the spark is only going to be
strong enough to jump the spark plug gap. If you widen it to .035,
the spark will still be fine under most conditions with the stock
coil except for maybe full load at higher RPM’s. The later V12 HE
engines running 12.5/1 compression and a very hot spark courtesy of
Marelli still run a .025 spark plug gap. No reason to run a wider
gap. Most manufacturers that switched to the wider gap and
resulting higher output spark coil(s) did so to ignite a much
leaner mixture than is present on the XKE. Putting a wider gap on
the plug when not needed only stresses the other ignition
components
Nick