Dear E-Type lovers,
What are the best spark plugs to use for a 1974 E-Type V12?
Regards.
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
Thank you Nick,
Great info - very informative. I have a 74 late V12 engine so I’ll stick with the Champion N9YC plugs gapped at 0.025.
FYI: the manual calls for N10Y plugs. The “C” at the end is for a copper core which gives the plug a wider heat range. Champion changed to a N9YC to cover the N10Y and the N9Y plugs.
1 Like
Thanks Dick for joining…(hope ok to quote your prior). So how does the oft used Champion N11YC or N12YC fit into the Champion range. Is this a revised number system for the heat range ? If not…wouldn’t those be quite a bit hotter plug than the N9-10? And…what is the current cross to the old system N5? thanks…Nick
The N5 is now the N5C, and the N11Y is (I believe) N11YC. During production of the 4.2 S1, the factory apparently received complaints of engine fouling when cars were used regularly in heavy traffic, so they made the recommendation to switch to N11Y.
Interestingly, my original owners manual from 1967 says N5, and a later repro copy says N11Y. The Clausager book says the change was made in October 1966, 747 engines before mine, so they had a few owners manuals stacked on the shelf to use up!
I’ve been using N5, then N5C in my 50 years of ownership, as I was not aware of the change until recently.
I am curious that the N5 designation is in the same numbering system as the N9 , N11, N12…??? that would be a huge jump in heat range (N11-12 much hotter than N5.) But it seems to be the case, as Jaguar did issue at least two XKE Service Bulletins to change to hotter plugs, as there were complaints of fouling. Service Bullletin B44, Sept 1966, “isolated instances have bee reported of N.5 Sparking Plugs fitted to 4.2 litere “E” Type Engines becoming fouled…hard start…plugs should be changed for a set of Champion N.11Y…” and the factory made this change in production to ALL 4/2 near March 67, with Service Bulletin B B46, even tho stating it was to aid in slow city traffic. I still believe the N.5 is not in the same numbering system as the later N.9, 11 and 12. There was a Champion numbering system change…I just don’t know the details of it…still searching for that info. All the N5 to N5C is, is addition of copper. N5 replaced the NA-8, approx July of 1957. The “Y” is for the projected central tip which means the electrode is also projected, deeper into the combustion area, and this provides improved heat range and fuel ignition, but there must be clearance for the projection. Plug "reach: data does NOT include the projected tip…is the seat to end of thread measurement.
All of these: N8Y,N9Y,N9YC, N10 cross to NGK BP6ES. All of
these: N11Y,N11YC, N12Y cross to NGK BP5ES, a hotter plug.
BP7ES would be a colder plug.
In NGK the lower number is hotter, in NGK the heat range is
much wider than in Champion, for a given plug. The P is
projected tip. The BP6ES is a good plug to start with,
hotter is the 5…The 7 likely only for sustained very hi revs. You can see that Champion has narrower heat ranges for a give plug, with several crossing to a single NGK plug. THIS wider heat range in one plug is why some choose the NGK. If you drive kinda the same way all the time…the narrow range can work. The factory did indeed change plugs because the N5 did not always work. It was prone to foul in city traffic. Jaguar went for hotter plugs, but the mechanics rule is Always err on the cold side…the plug could foul, but too hot can cause piston damage rather quickly…like very quickly if in spirited driving or racing.
Nick