4.0 XJR - What should they be capable of - delimited ?
Discussion
In all likelihood, it's probably close to max anyway. It just sounds better to say that you've limited it to 155, rather than it maxing out at 157.
I'm not sure if it works the same with an auto box, but with manuals, manufacturers tend to gear the car so that it can produce optimal power and torque within the limited speeds.
Manfacturers also design the other components to work to their intended maximum speed. I remember speaking to a guy from Noble, who explained that they could easily engineer the M400 to max at over 200, but they have a maximum designated top speed of 175 because it would be too expensive to design brakes, suspension etc to cope with such high speeds. You might get the Jag to 170, but find that the front wheels are no longer in contact with the road, the suspension can't cope with the speed, and the brakes catch fire when you try to stop.
But, in theory, yes, all you need to do is remove the limiter on the ECU (which will invalidate any remaining warranty, and probably your insurance).
ETA: It would appear that the limiter is not necessarily using the speed indicated on the speedo. Speedos usually read ~10%~ over - so actual 155 would be an indicated 170 on a speedo. Someone I know was demonstrating XKRs on a track when the new ones were launched, and was driving the new one back-to-back with the old one. He said that at one point he saw over 170 on the speedo of the old XKR, when it was supposed to be limited to 155.
Car mags have also noted similar experiences with other "limited cars" - I remember one of the car mags writing a review of the M5 when it came out, saying that it was still accelerating hard at an indicated speed of 170.
I'm not sure if it works the same with an auto box, but with manuals, manufacturers tend to gear the car so that it can produce optimal power and torque within the limited speeds.
Manfacturers also design the other components to work to their intended maximum speed. I remember speaking to a guy from Noble, who explained that they could easily engineer the M400 to max at over 200, but they have a maximum designated top speed of 175 because it would be too expensive to design brakes, suspension etc to cope with such high speeds. You might get the Jag to 170, but find that the front wheels are no longer in contact with the road, the suspension can't cope with the speed, and the brakes catch fire when you try to stop.
But, in theory, yes, all you need to do is remove the limiter on the ECU (which will invalidate any remaining warranty, and probably your insurance).
ETA: It would appear that the limiter is not necessarily using the speed indicated on the speedo. Speedos usually read ~10%~ over - so actual 155 would be an indicated 170 on a speedo. Someone I know was demonstrating XKRs on a track when the new ones were launched, and was driving the new one back-to-back with the old one. He said that at one point he saw over 170 on the speedo of the old XKR, when it was supposed to be limited to 155.
Car mags have also noted similar experiences with other "limited cars" - I remember one of the car mags writing a review of the M5 when it came out, saying that it was still accelerating hard at an indicated speed of 170.
Edited by Dominicc01 on Monday 14th June 10:05
Interesting points, I guess that there is a grey area. i have never understood why speedos never appear to be accurate, even technology of 10 / 15 years ago you'd have thought they would get it right.
I rteckon the speed on the sat nav could be more accurate, however there are considerable variables affecting both methods I'd have thought.
I rteckon the speed on the sat nav could be more accurate, however there are considerable variables affecting both methods I'd have thought.
I have an '99 XKR with the speed limiter removed.
My SatNav shows the speedo is 5mph fast all the way through the speed range
If the XJR has the same diff ratio and tyres as the XKR then rev limited to 6,200 in fith will be 198mph
Not sure if it would pull that though
I have shown 180mph on the SatNav before my engine upgrades, I would be looking to get into the 190's now
I do have an Arden body kit fitted that does help stop the front going light
Also brakes and susspention arn't standard
Last year I gave a XJ220 a good run for it's money hope to do even better this year at Dunsfold
Please not speed quoted were on private land or Germany, not on the Queens Highway
My SatNav shows the speedo is 5mph fast all the way through the speed range
If the XJR has the same diff ratio and tyres as the XKR then rev limited to 6,200 in fith will be 198mph
Not sure if it would pull that though
I have shown 180mph on the SatNav before my engine upgrades, I would be looking to get into the 190's now
I do have an Arden body kit fitted that does help stop the front going light
Also brakes and susspention arn't standard
Last year I gave a XJ220 a good run for it's money hope to do even better this year at Dunsfold
Please not speed quoted were on private land or Germany, not on the Queens Highway
CraigW said:
I think an XKR would need a huge amount more power to get into 190's, 180 true mph is astonishing, to get another 10mph at that kind of speed would be more like a miracle and you'd need about 5 miles to do it in. All imho but i'm pretty sure I'm right.
TrueBut my engine/supercharger upgrades can release 650 horses
NormanD said:
I have an '99 XKR with the speed limiter removed.
My SatNav shows the speedo is 5mph fast all the way through the speed range
If the XJR has the same diff ratio and tyres as the XKR then rev limited to 6,200 in fith will be 198mph
Not sure if it would pull that though
I have shown 180mph on the SatNav before my engine upgrades, I would be looking to get into the 190's now
Last year I gave a XJ220 a good run for it's money hope to do even better this year at Dunsfold
I would imagine you would obliterate a stock 220 to 100+ as they are awfully hard to get moving until you hit 3rd.My SatNav shows the speedo is 5mph fast all the way through the speed range
If the XJR has the same diff ratio and tyres as the XKR then rev limited to 6,200 in fith will be 198mph
Not sure if it would pull that though
I have shown 180mph on the SatNav before my engine upgrades, I would be looking to get into the 190's now
Last year I gave a XJ220 a good run for it's money hope to do even better this year at Dunsfold
NST said:
GavinPearson said:
Bear in mind that an XJR is a lot less aerodynamic than an XK so it will never go as fast for the same power levels.
How much faster is the xkr 4.0 over the xjr? Would 180mph be possible?did jaguar ever test the cars above 155?
Cheers
That said, it might creep up to that speed slowly, hit the rev limiter and or restrictor, but either way, the speed should be attainable.
If you are able to mess around with PCMs & TCMs you could fit a 15HU rear diff with a 2.88:1 Pow-r-lok on an XKR and achieve the top speed if you were getting rev limited.
richw_82 said:
One of the former test engineers got his XJR6 up to 158mph at Woodbridge the other year. If he can't get it to go much faster I don't think anybody will.
Regards,
Rich
I suspect that's a bit of a false statement. You'd need to know why it wouldn't go any faster.Regards,
Rich
Top speed is much about power and gearing and to a degree aerodynamics, but the latter is highly related to power.
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