Colder sparkplug for s/c AJ-V8 ?
Junior Member
Joined: Feb 2018
Posts: 20
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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
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
Last edited by Cambo; Jul 8, 2018 at 04:00 AM.
Junior Member
Joined: Feb 2018
Posts: 20
Likes: 1
And this all got me thinking about the 5.0L engines, what's the story with the plugs on them?
And I found something interesting!
If we look at the X150 XKR with the 5.0L, there were different plugs specified for the regular 5.0L XKR, and the XKR-S.
XKR from B32753 to B45394 = AJ812146 = NGK ILKAR6C-10
XKR from B45395 onward = C2P23089 = ILKR6C-10
XKR-S from B32753 onward = C2P23089 = ILKR6C-10
The C2P23089 is the same plug used in the F-Type V8.
What i see from the various technical manuals is that the 5.0L plug ILKR6C-10 gap is defined as 1mm, no range given. This ILKR6C-10 is shown in the XKR manual, also the F-Type manual. Safe to assume that the gap range is going to be 0.9mm to 1.0mm, and they are probably 0.9mm straight out of the box.
Funny enough the 3.0L AJ126S is spec'd as SILZKAR7C-10S, gap 0.9-1.0 mm
So yeah! The AJ126S runs a colder plug (7) than the AJ133S (6).
It was mentioned in a thread here on the forum about someone putting a tune in an F-Type, and the tuner recommended going to a colder plug. I suppose that's going from a 6 to a 7. Hope they got the gap right!
Here is a 7 plug that looks to be the right one for the 5.0L https://www.ngk.com/product.aspx?zpid=9824
And apparently there is an 8 version which was used on the AMG SLS as an OEM part...
And I found something interesting!
If we look at the X150 XKR with the 5.0L, there were different plugs specified for the regular 5.0L XKR, and the XKR-S.
XKR from B32753 to B45394 = AJ812146 = NGK ILKAR6C-10
XKR from B45395 onward = C2P23089 = ILKR6C-10
XKR-S from B32753 onward = C2P23089 = ILKR6C-10
The C2P23089 is the same plug used in the F-Type V8.
What i see from the various technical manuals is that the 5.0L plug ILKR6C-10 gap is defined as 1mm, no range given. This ILKR6C-10 is shown in the XKR manual, also the F-Type manual. Safe to assume that the gap range is going to be 0.9mm to 1.0mm, and they are probably 0.9mm straight out of the box.
Funny enough the 3.0L AJ126S is spec'd as SILZKAR7C-10S, gap 0.9-1.0 mm
So yeah! The AJ126S runs a colder plug (7) than the AJ133S (6).
It was mentioned in a thread here on the forum about someone putting a tune in an F-Type, and the tuner recommended going to a colder plug. I suppose that's going from a 6 to a 7. Hope they got the gap right!
Here is a 7 plug that looks to be the right one for the 5.0L https://www.ngk.com/product.aspx?zpid=9824
And apparently there is an 8 version which was used on the AMG SLS as an OEM part...
Senior Member
Joined: Jun 2012
Posts: 366
Likes: 220
From: newcastle
Just an update to this thread for anyone who is dabbling with colder plugs.
I put in 7 heat rated plugs in mine and they fouled at the 6 month point causing a serious misfire, I put this down to alot of recent roadworks in my area and sitting idling alot more than I had been. As the plug is not reaching the self clean temp the carbon deposits built up.
I have now reverted to standard 5 heat range plugs (due to non immediate availability of the 6 heat range ones that I was going to try).
I put in 7 heat rated plugs in mine and they fouled at the 6 month point causing a serious misfire, I put this down to alot of recent roadworks in my area and sitting idling alot more than I had been. As the plug is not reaching the self clean temp the carbon deposits built up.
I have now reverted to standard 5 heat range plugs (due to non immediate availability of the 6 heat range ones that I was going to try).
Just an update to this thread for anyone who is dabbling with colder plugs.
I put in 7 heat rated plugs in mine and they fouled at the 6 month point causing a serious misfire, I put this down to alot of recent roadworks in my area and sitting idling alot more than I had been. As the plug is not reaching the self clean temp the carbon deposits built up.
I have now reverted to standard 5 heat range plugs (due to non immediate availability of the 6 heat range ones that I was going to try).
I put in 7 heat rated plugs in mine and they fouled at the 6 month point causing a serious misfire, I put this down to alot of recent roadworks in my area and sitting idling alot more than I had been. As the plug is not reaching the self clean temp the carbon deposits built up.
I have now reverted to standard 5 heat range plugs (due to non immediate availability of the 6 heat range ones that I was going to try).
__________________
2008 XKR Convertible, (mods: AlphaJagTuning ECU Tune , 1.5lb pulley, (200cel cats( are now melted), xpipe, Bosch 001 pump, 180 Thermostat.
Drag strip : 7.9sec 1/8mi 90 MPH . 1/4 mile 12.55 at 112.98mph
432rwh Dyno on Mustang Dynometer , Approx 511 crank HP.
2013 XJ 5.0 SC (Alpha Jag ECU, TCU tune, crank pulley), 600+ HP, 11.6 sec 1/4th mi 122mph, 7.6sec 1/8th mi
2018 Jaguar F-Type (AlphaJag ECU TCU, lower upper pulleys intake) 10.77 ,131mph ,700hp
2008 XKR Convertible, (mods: AlphaJagTuning ECU Tune , 1.5lb pulley, (200cel cats( are now melted), xpipe, Bosch 001 pump, 180 Thermostat.Drag strip : 7.9sec 1/8mi 90 MPH . 1/4 mile 12.55 at 112.98mph
432rwh Dyno on Mustang Dynometer , Approx 511 crank HP.
2013 XJ 5.0 SC (Alpha Jag ECU, TCU tune, crank pulley), 600+ HP, 11.6 sec 1/4th mi 122mph, 7.6sec 1/8th mi
2018 Jaguar F-Type (AlphaJag ECU TCU, lower upper pulleys intake) 10.77 ,131mph ,700hp
Veteran Member
Joined: Dec 2008
Posts: 6,460
Likes: 2,582
From: Florida
I can’t for certain the cause. The colder range plugs are factory specified for hotter climes and the Aston version of the motor. How hard do you drive them? No issues with mine on modified tune but I also push the car hard and keep the revs within peak power band.
Veteran Member
Joined: Jun 2019
Posts: 1,710
Likes: 497
ive never heard plug temp relates to ambient temps. Ive been taught the plug temp relates to the combustion temp and pressure which is pretty much unrelated to ambient temp. If you dump gas in it the chamber cools, more boost hotter charge, more timing hotter chamber, etc so unless youre changing up a lot of stuff plug temps shouldnt change. And if your stock engine isnt burning right you gotta fix that and not start by changing to a diff temp plug.
Veteran Member
Joined: Dec 2008
Posts: 6,460
Likes: 2,582
From: Florida
The Middle East is an example of a market where colder plugs are fitted standard. Also my reason for colder pigs IS because I have a number of modifications where they DO make a difference.
Which ones you use? I got iriidium ngk 7 range no issues
__________________
2008 XKR Convertible, (mods: AlphaJagTuning ECU Tune , 1.5lb pulley, (200cel cats( are now melted), xpipe, Bosch 001 pump, 180 Thermostat.
Drag strip : 7.9sec 1/8mi 90 MPH . 1/4 mile 12.55 at 112.98mph
432rwh Dyno on Mustang Dynometer , Approx 511 crank HP.
2013 XJ 5.0 SC (Alpha Jag ECU, TCU tune, crank pulley), 600+ HP, 11.6 sec 1/4th mi 122mph, 7.6sec 1/8th mi
2018 Jaguar F-Type (AlphaJag ECU TCU, lower upper pulleys intake) 10.77 ,131mph ,700hp
2008 XKR Convertible, (mods: AlphaJagTuning ECU Tune , 1.5lb pulley, (200cel cats( are now melted), xpipe, Bosch 001 pump, 180 Thermostat.Drag strip : 7.9sec 1/8mi 90 MPH . 1/4 mile 12.55 at 112.98mph
432rwh Dyno on Mustang Dynometer , Approx 511 crank HP.
2013 XJ 5.0 SC (Alpha Jag ECU, TCU tune, crank pulley), 600+ HP, 11.6 sec 1/4th mi 122mph, 7.6sec 1/8th mi
2018 Jaguar F-Type (AlphaJag ECU TCU, lower upper pulleys intake) 10.77 ,131mph ,700hp
Veteran Member
Joined: Dec 2008
Posts: 6,460
Likes: 2,582
From: Florida
Gentlemen, if you read back through this thread you will see input and commentary from those well experienced and the reasons for application and heat ranges on plugs either climate based or use based.
If you live in a colder climate, drive in congested traffic frequently, do not have any modifications to the engine tune AND do not push the engine all of the time, then yes colder plugs WILL foul, etc, etc...
If you live in a colder climate, drive in congested traffic frequently, do not have any modifications to the engine tune AND do not push the engine all of the time, then yes colder plugs WILL foul, etc, etc...
Veteran Member
Joined: Jun 2019
Posts: 1,710
Likes: 497
Gentlemen, if you read back through this thread you will see input and commentary from those well experienced and the reasons for application and heat ranges on plugs either climate based or use based.
If you live in a colder climate, drive in congested traffic frequently, do not have any modifications to the engine tune AND do not push the engine all of the time, then yes colder plugs WILL foul, etc, etc...
If you live in a colder climate, drive in congested traffic frequently, do not have any modifications to the engine tune AND do not push the engine all of the time, then yes colder plugs WILL foul, etc, etc...
maybe cars in the Middle East are tuned with a different fuel map and ignition timing- both of those will change the compression temperature and might required different plug temps possibly but I’m not seeing climate as being the controlling factor. cars run from -10°f up to 115°f outside ambient temperature here in the US and they don’t change the plugs between summer and winter and the plugs don’t foul so if you can make the case for how a single temperature plug can run between -10° F 105° F here in the US but yet the Middle East needs a colder plug because its 105 there Id like to hear it