I understand Jaguar entered into a voluntary agreement with various other manufacturers to restrict the top speed of their vehicles to 155 mph and I am wondering if anyone has managed to derestrict one and if so, what is the true top end potential of an otherwise standard XKR.

This is a purely academic question - at least it is from me, as I know from experience on bikes that that sort of speed is very rarely obtainable with any degree of safety, but I can't help but wonder...........170?......180??

Also, I assume the restriction is carried out by the engine ECU limiting the RPM once the transmission module has registered it is in fifth gear and therefore presumably, one could create a device to interface between the engine and trans modules that would prevent the engine module from ever seeing fifth gear?

I know Suzuki did something similar with the Hyabusa and one could connect a small box of tricks into the main loom under the seat and hey presto....... one very fast motorcycle!

Andy

 

I believe the simplest way is to disable the ABS and use satnav to get your roadspeed.
Unless you're planning an audacious International diamond robbery and need to outrun the few cop cars that can manage >150 mph it seems a bit academic!

 

Didn't they use a black van a few weeks ago?

 

I understand from the previous owner that my car has been de-restricted though how and by what means this was achieved I dont know - niether (officer) do I have any idea of the top speed, or potential top speed. I just know that currently, my XKR is purring nicely

 

I agree it would be nice to know you were driving a 180mph car, even if you never use it. I mean, how many of us actually need/use 400hp+ anyway? It is my ambition to own a 1000hp car before I die, which is even more pointless given the current move towards the dandelion-powered electromagnetic pods they want us all to drive.

 

The 155 mph limit was for a time a voluntary, if somewhat arbitrary, agreement.

I've read Jaguar tested unrestricted XKR's to 178 mph at Nardo but can't turn up the actual reference to this.

Graham

 

I recently acquired a '99 XK8 and was a bit miffed to find out it was electronically restricted to 155. To paraphrase Bill Cosby, "I need a car that goes 180 mph to get to work in the morning." Is there any new insight into removing this restriction?

 

I have done 179 at the Milbrook Bowl in a derestricted 05 XKR

On a straight I am sure we could of gone faster

 

As I said initially, the question was an academic one, but clearly it is a pertinent one for someone on a track session etc. I am interested at a technical level how the system is restricted and how you would derestrict it. Perhaps XKRacer, you can shed some light on this please?

I seem to remember reading somewhere that a derestricted XK8 probably wouldn't go much quicker than 155, but the XKR might have the potential to reach 180+ mph.

I fully agree that for the majority of owners, myself included, 400 hp and 155 mph is way more than is ever needed, but I'm with Frog........you can never have enough power.

Andy.

 

This board is full of actual engineers. Surely someone knows the math to calculate theoretical speed given RWHP, gear ratio and weight.

Any takers for this challenge?

 

You actually left out drag coefficient, which I suspect is very low (and lower for the coupe), and I would guess is one of the reasons that these cars can attain such high top ends.

 

It is my understanding that a standard XKR can reach 180 mph and the 155 mph limit can be defeated by pulling a fuse that also disables the speedometer. There is a thread on this forum (I think) that I read a couple of years ago about doing this but I can't find it now.

Mark

 

I recall seeing the same.

 

Pulling the fuse will also disable the speedometer, thus requiring a GPS. An ECU tune removes the speed limiter.

 

Hey I'm still waiting for someone to figure out how to make my windows one touch up in addition to one touch down (apparently a feature that the 2006 models had). I would think derestricting/delimiting the car would be even more difficult.

Doug

 

The fuse story I believe is one of mine....
It is how I went around the bowl so fast, my driver took a couple of fuses from the left hand side engine bay, the abs did not work neither did the speedo.

Trust me I did ask but he said he was sworn to secrecy by Jaguar and would cost him his job, it took him seconds!!!