First, I'm not a car fixer but i enjoy driving. Saying this because i don't know much about the mechanical workings of engines and the other stuff in a car.

I do know that i want a car that will have the fun and thrill of quick acceleration. I tried the 07 XK and it was great, very fast from the start. I then tried an 04 XK8 and it took a second or two for that to kick in, so not as thrilling.

First question is if this is to be expected or if there maybe was an issue with that particular XK8.

Second thing, the XKR name didn't change in 07 like the base name did. Does that mean it's the same engine in both generations?

Or, would the 06 and older XKR engines be similar to the 07 XK base?

There are very few around me to test drive, but i know I would be happy with 07 XK performance. But didn't know if i would need an 06 or older XKR to get the same in a lower price.

 

The XK8 and XKR of the late 90's through 2006 are designated as the X100 models.
From 2007-2015, the car was called XK (sometimes called "New XK" in advertising materials) or XKR and are designated as X150 models.

The basic engine design was not radically changed from the later X100's to the early X150's. There were minor tweaks improving the power of both the normally aspirated cars (XK) and the supercharged cars (XKR). The chassis, styling, body construction, etc. were radically changed between the X100 and X150.

 

Most importantly added to the above comment...... The X150 new models are all-aluminum alloy bodies and not the steel of the former X100 XK8s. Also on the engine, VVT was added for the newer cars. Oh yeah, and the chassis on the X150s are VASTLY superior to the older ones.

 

Thanks for the replies. Regarding the engine, it sounds like there wasn't that much of a difference between the 100 and 150. But as i mentioned, the xk8 i drove accelerated much more slowly than the 07 xk. That sounds like it may have been an issue with that particular car then, perhaps?

 

At least on my x100 xkr, if you don't have the sport button pressed, you start in second gear. That obviously hampers things. They seem to be higher geared in general too.

 

Interesting! That sounds like it could have been the issue. I'll try again and see if that does it. Thanks!

 

We moved from a 2003 XKR (X100) to a 2007 XK (X150).

The 2007 Normally Aspirated X150 feels faster to us than our Supercharged X100 did. Clearly, nothing scientific, but my wife and I both noticed it, especially at launch.

 

This was a comment in the period press writings as well.

I would hazard to say without looking up figures that peak power did not change much; power across the rev range did below peak power must have flattened out, causing a substantial increase in lower RPM torque.

Then there is gearing and the transmission shift times that may have changed, and a lighter weight car.

 

The X150's are several hundred pounds lighter than their X100 predecessors. This surely accounts for some of the difference. I would also guess the drivetrain response on the X150's is programmed to be more aggressive, i.e. tending toward the role of a sports car more than a comfortable touring car. As mentioned above, the suspension is also revised on the X150's, contributing to the sensation of speed and urgency over the XK8's sense of comfort and luxury.

The underlying confusion of the moniker XKR for both the X100 and X150 remains. You can think of it as:
1997-2006 X100: offered in N/A (XK8) and supercharged (XKR)
2007-2015 X150: offered in N/A (XK) and supercharged (XKR)

The supercharged version of either is alway just called XKR. For the sake of avoiding confusion, I'm not mentioning special editions or other variants of the cars.

 

The '04 and '07 should have the same engine and tranny. Although from what I see they tweaked out an extra 20hp with the updated body, 420hp for the '07. You had a smidge more HP and a weight reduction in the body. But who knows, the '04 may have been a dog of a car like you say. You would need to try another '04 to know for sure.

 

If memory serves correctly, there are issues with the XK8 and XKR (X100) throttle cables that allow too much slack. The never allows the throttle to open as much as the pedal input should. Perhaps this was the reason for the restricted performance.

 

This absolutely is a thing. Basically with a scan tool hooked up, floor the car while off. If at the floor it doesn't read 100% for throttle position, you can adjust it and get that back. Really simple and it should be done whenever the throttle body is removed.

 

Tampamark's HP reference is to the supercharged cars. The '06 XK was rated at 294 HP. The '07 was 300. Not much difference by itself. However as noted above there were other changes which may have contributed to the difference you noted.

You might want to try a 2010 XK with the 5.0 engine making 385HP. That makes a real difference.