| In reply to anyone still confused about Iridum plugs for the 300Zed TT I posted a few days ago a debate. Well I contacted Jon MacQuarie at NGK in the US to clear this up after he said their Iridium IX COULD be used for the TT. I mentioned we were still witnessing a confused debate on here and asked him to look at our posts. Here's what he replied to us all. Comments?
Hello,
The spark plug designed for the 300ZX uses a special design. The spark plug
has a extra long projection with an extended shell.
The purpose of the long projection is to ignite the A/F mixture deeper in
the combustion chamber, allowing fast flame kernel growth as well as good
anti fouling characteristics. Since the PFR6B-11B uses an extended projection, the insulator needs to be
protected from thermal shock. Thermal shock is the heating and cooling of
the insulators firing end. If you look at the PFR6B-11B firing end you'll
notice the insulator is narrow and gets wider the further down in the shell,
like all spark plugs. The insulator tip is hotter than the insulator down
inside the shell. The difference in temperature can cause insulator
breakage. If you notice the PFR6B-11B is a 3/4 thread reach and has a
section past the threads, which has no threads. This section is designed to
prevent thermal shock on the insulator and enables us to reduce ground
electrode length from the weld to the bend. If we didn't use the shell
extension the ground electrode would be very long from the weld to the bend.
This would make the ground electrode prone to failure. We don't list an iridium spark plug due to the fact we don't make this exact
design in iridium. For liability issues we won't list an iridium spark plug
for this application due to it's special design. However by calling or
emailing we can make the recommendation of an iridium spark plug with less
projection, especially in modified applications. Of course the end user
will use at there own risk. In modified applications you don't want as much
projection as a daily driver so performance isn't an issue. You can use the iridium spark plugs BKR series in this application. Again
it will have less projection then the spark plug originally designed for the
vehicle. Jon MacQuarrie
Technical Support Specialist
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