That "Jaguar Document" about top speeds is a good read if you have a 2002 straight XJ8, but I see nothing that mentions anything younger then that. Those were good cars, but to compare a document put out by Jaguar referencing 2002 cars, to say, an 04 or 05 XJ8 or XJ8L car, is a bit off the track. These cars look a lot similar, but once pass the looks there is no comparison--with the exception of maybe some mechanical issues--. Just to mention one aspect, the 05 cars, with the exception of a few under body suspension parts, are ALL aluminum--built like an airplane--with rivets and adhesives. Nuts and bolts used only to hold on finders etc. Yes sir, quite a different CAT. So the comment that all US Jaguars are limited to 121 MPH, is a mute statement.

2004 XJ8 & Sport mode - one man's opinion
 

In my personal experience with my 2004 XJ8, also an aluminum bodied car, I found that the real world action of the selection of Sport Mode mirrored what the driver's handbook stated.


If I chose Sport Mode on EITHER side of the J-gate the upshift RPM's in full auto were extended to about 6600-6700 (based on tach readings). To the extent that such an increase keeps the car closer to it's horsepower and torque peaks it would in each gear give a higher speed that it would have attained had it shifted at it's more normal 6000-6100 RPM's,. and it would get there quicker. The shift points are slightly more aggressive but still very smooth in each gear all the way through to 6th with a similar run to 67-6800 in each successive gear.


Since both 5th and 6th gears are in fact overdrive ratios designed for higher mileage and quieter cruising they wouldn't be my choice for a top speed run. I'd pick 5th and maybe even 4th as that would certainly keep the engine nearer it's power peak in the RPM range. With maximum HP (293) coming at 6100-6150 RPM's and torque peaking at just about 400lbs. at 4200-4300 RPM's you can see that keeping it limited to about 3400 RPM's in either 5th or 6th as was seen by Blairware in a post on 12/21/2014 is well short of the motors potential even given an increase in aerodynamic drag as the speed picks up.

I'd think that if the speed were NOT electronically limited the XJ8 would be capable of something near 135. Given that in 2004 the standard 17" and optional 18" wheels came fitted with "H" rated tires with a speed rating of 130mph a limit of 122mph makes sense. Oddly enough the 19" & 20" wheels came equipped with "Y" rated tires that max out at 186 mph!

Not really Chuck as electronic speed limiters don't care if the car is 3800 libs or 4000 lbs. as they are calculated to react to the computerized speedometer's speed reading. The fact that the car weighs some 200 lbs. less than a similar steel bodied car (that's all the difference there is) just makes it a slightly faster accelerating car and more fuel efficient.

Both 5th and 6th are overdrive gears and thus don't allow the engine to operate at it's full potential. If anything 6th gear would reduce the top speed in a speed unlimited car although maybe not in our limited XJ8's.

When I took possession of my 2005 Jaguar XJ8L last March, it was equpped with Pirelli P235/50 ZR18 97W tires. What I also know is that the original owner sold the car to a Florida woman with roughly 40,000 miles on the odometer. It had about 78,400 miles on the odometer by the time that the woman traded it in to a Florida dealer in the Fall of 2013. I believe that she decided to peddle it some time after air suspension problems started developing (and attacking her pocketbook). Well, enough with the history.

After changing the air suspension over to coil/shocks, I purchased a set of Bridgestone "W" rated tires for the vehicle a week later. I'm guessing that the Pirelli tires were still the originals so I can't help wondering why that particular vehicle with a speed limiter on it would be equipped with 150 MPH rated tires.

According to the Jag literature I have the standard tire for a 2005 XJ8L was"


2005 XJ8, XJ8L 235/50 HR18 All Season Dynamic 8-Spoke 8x18

Well, apparently either the original owner or the Florida woman requested the higher rated tires. It seems plausible that the car is capable of attaining nearly 135 MPH, and that sounds about right to me.

Huh? That is the press release for the X350 so is very relevant!

The non supercharged 4.2L X350 in the rest of the world was limited to 155mph so the US version should be able to at least achieve that with the 121MPH limit removed as it is only 6bhp down on those cars.

As a guide the UK 3.0L V6 X350 had a top speed of 145mph and the 3.5L 150mph. The 4.2L XJ8 and XJR were limited to 155mph.

Would the non-supercharged versions of the 4.2 liter have enough horsepower to overcome the air resistance in attaining 155 MPH?

The 4.0L XK8 had 290bhp and that was also limited to 155mph so I don't think it is out of the question. I had my 1996 XJ12 up to an indicated 150mph and it still had some more to go.

my 1994 xj12 would only do 130 it had 4 speed, as for xk models they have always been governed at 155.

124 mph or so
 

My 04 xj8 will do

200 kmh or 124 mph or so....

Limiter takes over and holds the car back, she is still accelerating nicely intill the limiter kicks in.

Have had it there MANY times.... I will try in 5 the gear next time and see what it does. I doubt it will override the limiter!

Tom

This reminds me of USA S-Types apparently being limited whereas non-USA ones are not (by way of example my STR came with ZR tyres). I suppose it would be some sort of geographically-based marketing/etc reason.

Can you not simply program in one of the software versions from another region? Quite cheap to try.

Just Might Be 155 MPH
 

I’ll Gladly Be That Dare Devil. I Once Had A 2004 XJR & It Did Every Bit Of 170 MPH . 155 is nothing I’ll Be Getting a XJ8 VP (vanden plas)

Well, when I did reach 110 MPH at the time, I also began to smell fumes. It seems that I also smell fumes sometimes when I really step on the gas. In any case, the 2005 Jaguar XJ8L was earlier converted over to coil/springs so I'm not sure that I would have wanted to take the car over 130 MPH anyway (as the front end would likely begin getting light). In addition, I was rapidly approaching traffic down the expressway so I had to back off on the accelerator. Yes, my hands began feeling 'greasy' too.

Top speed with limit is 155

Have yet to see what top end is, i know a hundred is nothing when passing someone if your not watching just how fast you are going.

100+ is just a tap of the pedal on a SV8

Top speeds are computer limited
 

I've seen repeatedly over the years that the non-SC cars are limited to the low 120's while the SC cars are limited to 155, at least here in the states where we have the space in some areas to really let them rip.

Why that may be so is up for debate but I suspect it's tied to liability, tire ratings and durability, and most importantly (and tellingly) the governments not wanting the roads flooded with cars that can easily outrun the state troopers whose cars generally top out at 150.


That doesn't mean that some tuner somewhere can't 'hack' the system but I suspect for the vast majority of original Jaguar buyers speeds over 100 are generally not high on their list of priorities. Besides if they wanted a land based missile their are any number of foreign and domestic offerings that offer such thrills for less money.

In any case 100mph or more is easily achievable by both the SC and non-SC models with either 4.0 or 4.2 V8's and getting their is probably achievable in under 15 seconds or less. Next time you rocket by some lane lizard who is doing 60 in the passing lane consider what would happen if he, or she, were to suddenly switch lanes as you approached out of fear...which over rides thought.

The thought of it is bad, just bad.