In 2006 (USA spec), the STR and the XJR had their supercharged engines uprated to 400HP/413TQ, while the last of the 2006 XKR (steel bodied) remained at the previous rating of 390HP/399TQ. Anyone know what the changes were in the AJ34S engines in 2006? I've done a search and not found anything useful. It sounds like the last of old XKR were lumbered with the old spec engine?

 

I don't know what they may have changed besides the fact that they added variable valve timing to the supercharged V8s. It was already on the NA V8s.
So maybe they also did a re-tune of the ECU and were able to get a bit more out of the engine.

I was kind of surprised they left it off of the first series of engines.

Anyone know of any other changes?

 

I just did a quick CarFax scan of the several 2006 XK on Autotrader.com, and every one for which I could view the data was shipped to the US in the first quarter of 2005. So I'm guessing that all the "2006" XK were really built in early 2005 and thus carried the 2005-spec engines. Even NA V8s went from 294HP/303TQ in 2005 to 300HP/310TQ in 2006 (but not the poor 2006 NA XK which remained at 294HP). So what the devil happened for 2006? Just curious....

 

Just a new way of rating power was adopted resulting in higher hp and trq.

 

That apparently did happen. (This was discussed a few months ago.)

 

OK - I guess I missed that discussion.

What threw me is that I am holding in my hands the 2006 Media Information pack put out by Jaguar USA (a very impressive ring binder document with an attached CD). In it, Jaguar write (and I quote):

o "S-TYPE and XJ models with 4.2-liter V8 engines now boast 300bhp and 400bhp for naturally aspirated and supercharged, respectively"

o "Naturally aspirated 4.2 AJ-V8 now rated at 300bhp [SAE]; supercharged 4.2 AJ-V8 now 400bhp [SAE]" {for the 2006 S-TYPE}

o "Naturally aspirated V8 now produces 300 bhp SAE [up from 294bhp]" {for the 2006 XJ}

o "Naturally aspirated 4.2-liter AJ-V8 produces 294bhp [SAE], while supercharged 4.2-liter AJ-V8 delivers 390bhp [SAE]" {for 2006 XK}

All in the same Jaguar document for the 2006MY - a bit confusing!

I did a bit more searching just for my peace of mind and found discussions on the new SAE certification standard proclaimed in 2006, e.g.:
http://www.sae.org/certifiedpower/details.htm

So, yup, that explains the confusion in Jaguar's own 2006MY AJ-V8 advertised ratings. With the "2006" XKs all being built in 2005 prior to the new certification standard, they could not claim the new 2006 SAEJ1349 ratings for the "2006" XKs. Even though it is all the same engine.

I'm learning.

Now, classroom, for our next exercise - could someone explain the differences in the 2009 4.2-liter supercharged engines?
2009 XJ Super V8: 400BHP/413TQ
2009 XF Supercharged: 420BHP/408TQ

Huh? Differences in ancillary components/installation? That much? Or different engine details?

(Of course, in 2010 Jaguar went to the 5-liter Gen III monster motor, but that is a whole different kettle of fish.)

 

I understand that there are a number of changes in the XF SC (air filters, intake, TB, TB elbow etc and there will be a revised calibration for the PCM), which may well have led to the +20HP over the STR. No idea how many, if any, of those changes also apply to the XJ variant you list.