Hello, Jaguar people!

So, I've been an owner of an STR since last summer, and it's been a mixed bag of feelings tbh. I love the car aesthetically, especially the interior. At 36 young, it reflects my taste and the kind of vibe I think a car should have like 100%

However, I do have problems on the performance side of things. The car definitely isn't slow, especially above 100 kph, it does accelerate kinda relentlessly. However, I still find it a bit ...lacking. So much so that I've put it up for sale, but recently I started wondering whether there might be actually something wrong with the car. Unfortunately where I'm from, these cars are extremely rare so it's unlikely I could get ahold of another one for a comparison.

It's all pretty much my mistake, too. I have had some relatively powerful cars before, in fact my last daily before the STR was a ~ 260hp/400nm Saab. But then I made this switch for +150 more horses, more torque and the Jag is also my first rwd car. So to be perfectly honest, when test driving it before purchasing, I chickened out and didn't floor it. I was just concentrating on handling, rattles, weird noises etc, I never thought I wouldn't find it quick enough, and I was a bit afraid I might not be able to handle it or whatever...well, noob mistakes I know

Since I had the car, I tried doing a few 0-100 (0-60) runs. Not constantly as I don't want to thrash it, but when I tried, I was never able to get it under 6s. With TCS on, it just intervenes very aggressively, with it off, there's no grip. Tires are not the best there is, but they're fine. And the car goes, but there's no feeling of it pushing me back into the seat.

Anyway, I decided that before committing to selling it, it's about time I start to be a bit more scientific about this. I have a dragy so I'm gonna try to do a few runs, and maybe also take it on a dyno?
Those of you who dynoed their car (stock), what kind of rwhp did it make? I know it's supposed to be a 15-20% drivetrain loss, but it would be good to know what actual values were others getting as a benchmark.
Also, are you able to get the quoted ~5.5s to 100? Or even better?

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I wrote the above a couple days ago, just didn't post it yet. So I've just taken the car out with the Dragy, did a few 0-100 runs. 5 degrees C out there, so should run fine, right? Tried my best to get off to a good start.
Well, what do you know...my 3 times (when I didn't mess the start up) ended up being 6.72, 6.73, 6.77. Pretty consistent. Consistently bad. Something's wrong, isn't it? More than a second slower than it should be :\

 

Let's begin with some basics:

• What MY is the vehicle?
• How many kilometres/miles are showing on the odometer?
• What does the service history show?
• Is the MIL on, and if so, what DTCs are stored?
• What fuel is being used?

The X202 and later variants are luxury performance cars. If you need more performance, you should consider a supercharged X150 from MY2010 on or an X152 in R specification.

 

So I recently have gone through the trouble of getting a dragy and my car has managed a 13.09 @108 with a 4.8 0-60 “see below”. Granted my car is a 06 and I’m tune only at this point, but I’ve had similar numbers at the track when completely stock. Car does very well and keeps up with a lot of things one wound think would be quicker. Certainly wouldn’t be so quick to give the car the boot, might do a new set of spark plugs, I ended up getting NGK Ruthenium’s, and also a good set of tires. I have Toyo R888R’s on the rear and they’re as sticky as a pack of gum. I’m constantly tinkering with my car so if you’d like to follow the progression I’ve linked my YouTube down below. My instagram is the same as the YouTube.

https://youtube.com/@onefastboi14










Completely stock power figures

 

Hey, it's a 2003 with around 200k kms (124k miles) on the clock. Service history is kind of unknown, at least for the last third of it's age/mileage. No check engine light, no error codes. Fuel is standard european 95 octane (E10)...

I do understand that the STR is not a sportscar in the traditional sense, and while I do need more performance, it's quite possible that the car is capable of that, and is not delivering it due to some technical issues...

 

Holy ****, see, that's why I started wondering. 4.87 on a 0-60 run, that's almost 2 seconds faster than mine. Something must be off.
Thanks for that dyno data too. I'm taking mine to the dyno asap. Looks like the "standard" 18-20% drivetrain loss can be expected.

 

Other ideas:
1. blocked cat(s)
2. non-working SC coolant pump
3. wrong fuelling (AFR) e.g. misreading MAF

 

Thanks.I will dyno it just to have an idea of what's going on and if it's really missing out on power (more than a dozen or two hp), I'll make sure to take it to a specialist.

Wouldn't any of the above throw error codes?

 

iat2 dtcs aren’t set unless it’s close to maxed out

just touch the intercoolers if they’re hot change the pump

 

Certainly seem’s like something would be off. I’d be happy to update my Dyno numbers today after said tune. Taking the car to the original Dyno I went to, to have them check out the power figures as of yet. If you’re nearly 2 seconds off my 0-60mph figure I’d be interested to see where you are in terms of 1/8th mile and 1/4 mile figures. Something definitely sounds off.

 

Are there any untoward noises from the supercharger signifying bearing wear? Worn bearings can cause screw damage.
But if no weird noises, check everything else before stripping the SC.

 

Not that I can tell. Only noise I hear is a healthy-sounding supercharger-whine, but I'm neither a mechanic, nor a Jag/v8/SC expert.

Anyway, the car's going on a dyno next Wednesday, so I'll know more after that. Weird to say this, but I kinda hope it turns out to be down on power since then I can just get it fixed and keep it and hopefully enjoy it much more.

Thanks everyone, for all the answers and tips so far. Let's see how it goes.

 

Although, your tale reminds me of another. A guy some years ago bought a nice low mileage Jag but was a little disappointed with performance and fuel consumption. He had the car serviced and tuned, everything set up perfectly. Still the economy and performance were lacking in comparison to others of the same model. Eventually he found the problem when he checked the previous owners. It was originally an embassy limo, complete with armour plating. The extra weight made all the difference!

 

Lol, that's some story there. Mine does 13 mpg in the city, around 20 on country roads if driven moderately. I think that's about normal, isn't it?

 

My V6 3.0 X200 doesn’t do much better than that around town, but will easily do 25mpg on a long run. Considering yours has a bigger engine and a supercharger, that doesn’t sound too bad.

 

Yeah, I never thought the fuel economy was out of line.

 

Too funny! My ex-wife's father owned an ex-embassy Rolls Royce. It had the retractable glass partition behind the driver. They'd go for Sunday drives with the kids in the back. When they got too noisy, he'd raise the glass for some peace and quiet.

On a related note, never marry a woman who hates her father. Doesn't matter how pretty she is...

 

Well guys, the STR was just put on a dyno, and guess what. Clocked at 300 BHP. 290, actually. I'm not sure how reliable/professional this dyno was (it was a proper rolling road, no idea what kind though), because at the same time torque seems to be there, even more than stock. The measurement was stopped above 4300 rpm because the power curve basically became flat. So anyway, clearly something wrong after all.

We're gonna look into MAF, SC coolant and cats, also get some live data, if we can. Is there a boost pressure that these cars should be operating at?
I am going to take it to a specialist in any case, but wanna do some testing first with my local mechanic.

 

Be aware some OBD values are not reported at WOT.

I think boost is 13.

 

Chassis dyno numbers reflect WHP (wheel horsepower). Driveline loss is usually around 15%.

 

Yes, thank you, but I'm aware. We measured 290 at the crank using a 20-ish % estimated loss.