Colder sparkplug for s/c AJ-V8 ?
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.
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?
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.
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?
Last edited by Cambo; Mar 3, 2017 at 01:38 AM.
Popular Reply
Feb 23, 2017, 05:35 AM
Junior Member
Joined: Sep 2016
Posts: 7
Likes: 17
From: West Bromwich
I worked at Jag as a engine management cal engineer when these engines were being developed (still do infact).
The reason for the "5" heat range plug was to meet sign off for plug foul in extreme cold temperatures. The decision to keep NA and SC engine the same was to prevent NA plugs going into a SC engine by mistake at the factory.
Hot plugs do not cause detonation, they cause pre ignition. Which is very hard to detect, and very destructive. The standard tune on 4.2 SC's (and the NA's for that matter) is tuned to not get the spark plugs to hot. There is an area of the ignition map that is deliberately retarded for this, it is set by using instrumented spark plugs. And in this area the plugs will get hot enough to cause engine failure levels of pre ignition way before any spark induced detonation occurs.
Obviously, anybody trying to tune one of these engines in the after market will not be able to measure this. So fitting colder plugs is absolutely the right way to go. And as others have said, the Aston 4.3 plug is a direct fit.
Cheers
Sean
The reason for the "5" heat range plug was to meet sign off for plug foul in extreme cold temperatures. The decision to keep NA and SC engine the same was to prevent NA plugs going into a SC engine by mistake at the factory.
Hot plugs do not cause detonation, they cause pre ignition. Which is very hard to detect, and very destructive. The standard tune on 4.2 SC's (and the NA's for that matter) is tuned to not get the spark plugs to hot. There is an area of the ignition map that is deliberately retarded for this, it is set by using instrumented spark plugs. And in this area the plugs will get hot enough to cause engine failure levels of pre ignition way before any spark induced detonation occurs.
Obviously, anybody trying to tune one of these engines in the after market will not be able to measure this. So fitting colder plugs is absolutely the right way to go. And as others have said, the Aston 4.3 plug is a direct fit.
Cheers
Sean
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?
I know the coils on the AM are different to the Jag ones, but maybe the plugs could be interchangeable?
Veteran Member
Joined: Jul 2010
Posts: 7,362
Likes: 1,241
From: Austin tx and Daytona FL.
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!
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!
Veteran Member
Joined: Jul 2010
Posts: 7,362
Likes: 1,241
From: Austin tx and Daytona FL.
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!
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!
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?
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?
Senior Member
Joined: Nov 2011
Posts: 878
Likes: 324
From: Europe
Stroked 4.2 conversion, but all the electronics came from AJ26.
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Senior Member
Joined: Nov 2011
Posts: 878
Likes: 324
From: Europe
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...
Yet the Aston ones are 7 on the 4.3 and 4.7, and it's a naturally aspirated engine...
Senior Member
Joined: Nov 2011
Posts: 878
Likes: 324
From: Europe
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)
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)
Senior Member
Joined: Jul 2013
Posts: 422
Likes: 106
From: Wales, United Kingdom
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
And the Aston plugs are NGK IFR7N-10, this pretty much confirms what i've been thinking...
And the Aston plugs are NGK IFR7N-10, this pretty much confirms what i've been thinking...
Last edited by Cambo; Feb 19, 2017 at 05:56 PM.
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Joined: Feb 2015
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From: Nelson New Zealand
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 IRIDIUM POWER IK16 Spark Plugs 5303
Veteran Member
Joined: Feb 2015
Posts: 2,408
Likes: 599
From: Nelson New Zealand
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
Is the Denso 3356 Iridium (SK16PR-A11), which is a heat range "Denso 16" equivalent to NGK 5, which is the hottest range available.
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.
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).
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?
3.5L
4.0L (AJ27) n/a and s/c
4.2L n/a and s/c
Is the Denso 3356 Iridium (SK16PR-A11), which is a heat range "Denso 16" equivalent to NGK 5, which is the hottest range available.
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.
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).
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?
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...
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...
Veteran Member
Joined: Feb 2015
Posts: 2,408
Likes: 599
From: Nelson New Zealand
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...
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...
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 ,
