Hi all,

Owned an xk8 and now an xkr. Always curious about why Jaguar has limited the top speed to 155 mph. Is it a safety issue or corporate social consciusness (sp.?). And while I'm at it, is it possible/easy to over ride the limiter?

Thanks for any info,

Jon

 

US Fed regs.

 

Hlgeorge is correct, the federal government has limited your top speed. Why they allow bikes(even computer controlled) to run 180 and above baffles me. About the only way you can defeat the limiter is to get either a new ECM or new ECM programming from someone like Arden.

 

I have to disagree, or at least ask "Which federal regulation are we talking about?" Would this be a USA regulation or a European regulation .....or???

I've searched for any such USA federal regulation and have not found one, although I am perfectly willing to stand corrected.

Lots of other cars sold in the USA are not limited to 155 (Corvette, Porsche, etc) and Jags sold in UK and Europe have the same 155 mph limiter. In fact, many Mercedes, BMW, etc have the same 155 mph limiter as the Jags do, regardless of where they are sold.

I've heard, though not confirmed, that it was simply "by mutual agreement" from the big players that they'd all limit sedans/salons to 155 mph. <shrug>

Cheers
DD

 

Yeah, pretty sure that lots of cars in the US go over 155.

 

Not saying that they represent the final word but here are some tidbits:


Motor Trend:
Cadillac doesn’t subscribe to the German gentleman’s agreement to limit cars to 155 mph, so the V-series will test your sphincter’s fortitude right up to 191 mph, according to Cadillac (automatic versions are electronically governed to 175 to limit transmission output-shaft speed).

Forbes:
Historically, a gentleman's agreement in the auto business limited performance cars to a top speed of 155 mph, and many automakers still stick with that (mainly out of practicality; it's easier to certify a car's tires and other systems to go 155 mph than to go 205 mph)


Unknown:
http://www.autoblog.com/2005/07/14/manufacturers-may-lift-155-mph-limits/


Cheers
DD

 

Ids have to agree with Doug, and there are several reflash tunes avail for Jaqs....and Doug on the intercooler question from another thread, no still use the factory, only add a reservoir to monitor intercooler system coolant level

 

Ok, thanks ! Would I be pushing my luck to ask what reservoir you used?

It would save me the trouble of looking under the hood of 100 different cars looking for one that looks suitable

Cheers and thanks
DD

 

No, i used 1 from Stillen racing, for super charged intercooler system for Nissan Frontiers, Come with small bracket and coolant cap, upper inlet and lower outlet...Yes you need to fab additional hoses and space for reservoir, but youde be rewarded with totally seperate cooling system and more HP I would est, 10-20hp at full boost in summer, since I would think youde see a 100 degree drop in temps....But Im a firm beliver in testing before and doing a change and retesting to be more factual

 

From time to time I see these occasional posts about how to bypass the 155mph limiter and each time I scratch my head wondering who out there is actually finding it necessary to go 156mph?

Doug

 

Thanks for the details

Cheers
DD

 

Lots of things are not "necessary" but that doesn't stop us from wanting them


That said, going (155 or 156) mph is not something I'mparticularly anxious to do. If something goes wrong at that speed you're history. I have too many obligations in my life right now.

I won't say "never", though. One day the ideal situation may present itself.....

Cheers
DD

 

I remember a comment made on Top Gear by Jezza that the limiter is there because the car itself may not be able to handle the high speed stress (ie, turbulence) and start to shake violently (hence his argument for supercars which, unlike normal cars, are built to handle very high speeds). Added to that, if the car does not have the aerodynamics to keep itself planted at such a high speed, it would be quite dangerous to drive any way but straight.

 

No doubt those are considerations that went into the agreement to "not go there" and call 155 mph "good enough".

I gather, though, that some manufacturers are breaking ranks and dumping the self-imposed limit. Jaguar should do the same on selected models, as there is value in bragging rights....providing you have something to brag about, of course . For too long, IMHO, Jaguar has disassociated itself from its past performance image, with too many people thinking Jags are all elegance and no substance.

Cheers
DD

 

155mph is a gentlemens agreement.

I have had the coupe up to 155 and it is very comfortable until hitting the limiter. It is much more comfortable than my STi up there. My 360rwhp 2000 Trans Am WS6 was the most comfortable up there. The gearing was so tall that 5th was capable of 160mph and 6th was only able to do 155mph.
In 5th



I have done four cross country rallies, if you wondered why I have been in that area of the speedo so often.

Nick

 

I think the Fed regs have to do with the OEM tires the car comes with. To get the higher speeds, the car must come OEM with higher speed tires.

 

The tire manufacturers have a lot to say about the top speed limits as well

 

Yeah, the more you pay them, the faster the tire can go.

I picked up some tires rated at 186+mph for my car since it has seen the other side of 155 many times.

Nick

 

Fuel used to get to 155 mph on the Salt Flats....... $10.45

Enough beer to get up the nerve.......................$8.15

Losing control of the car while taking a digital photo of the speedo........PRICELESS

 

Who the hell was taking that picture at the time you were at 155+???

Doug