Colder sparkplug for s/c AJ-V8 ?
 

EDITED FOR ACCURACY 3rd MARCH 2017

The OEM sparkplug for the AJ-V8's

3.5L
4.0L (AJ27) n/a and s/c
4.2L n/a and s/c

I̶s̶ ̶t̶h̶e̶ ̶D̶e̶n̶s̶o̶ ̶3̶3̶5̶6̶ ̶I̶r̶i̶d̶i̶u̶m̶ ̶(̶S̶K̶1̶6̶P̶R̶-̶A̶1̶1̶)̶, which is a heat range "Denso 16" equivalent to NGK 5, which is the hottest range available.

EDIT

The OEM plug p/n C2A1535, which replaces AJ84575 is actually NGK IFR5N-10 for all markets except the Middle East, which use different versions depending on the vehicle model. For the 4.2L X150 XKR there are two versions for Middle East market cars.

Attachment 143519

C2A1535 = NGK IFR5N-10
AJ812842 = NGK IFR6N-10
C2C41805 = NGK IFR7N-10

IFR7N-10 is also the Aston Martin part number 6G43-07-10056

Gap range is specified 0.35-0.40 inches. (0.9 - 1.0mm)

The general consensus on the internet is that forced induction engines need a plug which is one or two heat ranges lower than naturally aspirated engines. So it's a little surprising to me that the OEM plugs are the same for both the naturally aspirated and supercharged versions of these engines.

There is an NGK equivalent to the OEM Denso plug, the NGK IFR5E11, heat range 5, same as Denso heat range 16. EDIT, these are the wrong gap

There is also a compatible plug from NGK that is one heat range cooler, the NGK IFR6E11 (from a 1.5L Mazda 3 of all things). EDIT, these are the wrong gap

I'm just wondering, for those of us with supercharged engines, who have smaller pulley's, engine tunes, etc, have we ignored/overlooked the spark plugs?

With a bit more searching I came across some info for the Aston V8 Vantage, they use an NGK 7 range plug. Spark Plug and Coil Options for 07 V8V - 6SpeedOnline - Porsche Forum and Luxury Car Resource

I know the coils on the AM are different to the Jag ones, but maybe the plugs could be interchangeable?

makes sense to use a colder plug for forced induction vs N/A, and correct most engine guys do that !

but i,m thinking only the super high boost engine make use of it!

way back 45yrs i used a flat gap plugs in a boosted chevy , like 35/40psig manifold pressure!

i tried some regular gap cold range plugs , one single blast drag track, burnt the electrodes right off the cold side , that was using cold Methanol fuel also!

but todays Iridium are lightyears ahead in sparkplug technology!

came across this pic at BONNEVILLE top speed track, i was a spectator,2007.

Sun coming UP over the horizon around 6.00/ 6:30 AM , 20 miles wide 80 miles long, clouds just breaking, deathly silent , no engines till 8:00 am!

sit out down track,folding chair , cup coffee, NICE start of a great day!

way off in back ground you can just see some cars pushing out to start area!

I have NGK 7.

According to JEPC the plugs for the AJ26 are not the same as the AJ27, AJ33, AJ34, AJ40, etc...

I forget now, did you do a 4.2 conversion in yours?

What's the exact part number for the NGK 7's you have?

NGK Iridium IX Spark Plug Part Number BKR7EIX-11 NGK Stock Code 6988

Stroked 4.2 conversion, but all the electronics came from AJ26.

Awesome, i'm off to buy a set now, might pick up a set of 6's as well, these things aren't too expensive.

Thanks very much you crazy Fin :)

I have bought mine from here: Sparkplugs UK | Denso | Champion | NGK Sparkplug & Glowplug & Lambda Sensors

You can see that their system gives 6 for stock AJ26S but for AJ27S or later just 5....hmmmm...

Yes this is the strange thing, AJ27 onward the OEM plugs are all heat range 5 regardless of supercharged or naturally aspirated.

Yet the Aston ones are 7 on the 4.3 and 4.7, and it's a naturally aspirated engine...

OEMs. are Iridiums from AJ27: AJ8 4575 (iridium) from 1999 MY
but NCA385OHA 2 for AJ26S and NCA385OFA 1 up to 1999 MY AJ26 N/A.
Maybe the material change explains the difference?

Perhaps Iridiums can be hotter than other types of plug?

But then the Aston plugs are also Iridium, and they are 7's, when the Jag Iridiums are 5's.

BKR7EIX-11 are also Iridium (and BTW listed as a direct replacement for the NGK IFR7N-10 which is the Aston OEM plug)

When I serviced my car last week I used NGK IFR6D10 which is one heat range colder than stock. Also used Mobil 1 0w40 oil (was on offer), instead of the usual 5w30. Definitely didn't add any power but it is running silky smooth!

Just to mention, if you order new plugs from jaguar you get NGK IFR5N-10

Attachment 142985

And the Aston plugs are NGK IFR7N-10, this pretty much confirms what i've been thinking...

i don't know exactly what heat range these correlate to but these are what i purchased as a direct replacement . they say heat range #5 on some of the ebay listings . but that doesn't say who's heat range that are comparing to .

DENSO IRIDIUM POWER IK16 Spark Plugs 5303

Denso 16 is the same heat range as NGK 5

oops i just noticed those details in post 1 . so do you think its wise to change & are your plans to change ? its lasted this long without burning holes in the pistons .

one thing i have noticed with the ford based jaguars . although striving to impress , they were also big on cost cutting . and it makes sense to me that the SC engine isn't in-fact running a too hotter plug but more like the NA is running what ever the bulk buy supplied ? i.e. the required plug for boosted application .
and it may have been necessary to use the heat range 5 plug for self cleaning reasons to achieve plug service intervals close to the 100000 km mark.

It's the opposite way mate. 5 is the hottest, 7 is cooler.

It's normal to use a cooler plug on a forced induction engine.

Which is why i'm miffed that the naturally aspirated Aston AJV8 runs a 7, and the supercharged Jag V8 runs a 5.

You're not going to melt a piston or break something by running a cooler plug, the opposite actually, hotter plugs are more prone to detonation...

sorry i had it right ,i was comparing jag SC VS NA not jag SC VS AM/NA

Maybe the sc is just right and the na is just gets what they had already bulk purchased .
as for the AM there must be a reason . my guess is the 5 will self clean for long life duration .
and the am probably wants to charge you for the more regular plug change ,