Not necessarily (although that is a great idea). What I meant was it should at least have been in the subject line or somewhere else in the post.

I am impressed that this is a pretty respectable 1/4-mile time for such a large/heavy vehicle.

Doug

 

completely agree with ya boss ^^^^^^ for their time the trans gearing makes up for crappy rear end ratio and even today standards low 5 sec 0-60 is impressive even new AWD WRXs arent doing it so quick.

 

My goal is to get it somewhere in the mid 12s while still looking stock

I like the sleepers.

I have plans for continuing progressive mods which will be revealed as they happen. I will post my progress as I make progress. Right now I'm waiting on a 4 lb lower pulley to be paired with my Snow Stage II dual nozzle meth injection. Like XJR-0220 suggested, I put the nozzles to spray into the charge coolers to continually steam clean them to keep them running at peak efficiency, that was a GOOD tip from him.

I hope to add the 3.5" true cold air intake soon after that and will report 1/4 mile times again.

Then the next set of mods will happen in the not too distant future. I'll be doing more because I don't think the above mods would quite get me into a 12.99 or faster yet.

Fun fun fun

 

sounds like badass plans boss and I think you will see some nice gains just by what you have done. Great to hear boss hope you kick some serious butt

 

I'm not going to yackity yack and only type about what would be good. I'm going to do "stuff" then show the results, and have some serious fun while doing it.

Some of my "future" as yet not yet revealed plans I think you will be impressed with. especially the results, but you will have to wait for them to be revealed after I get my track times

And yes, I will be kickin butt and taking names at the track!

 

thts what i like to hear so much better to be a shepard than a sheep and explore ur options not to mention just cus one person failed at attempting something dont mean it cant be done. edison tried making the light bulb so many times and when asked why he kept trying after he failed he said "I didnt fail I just found another way not to make a light bulb." lol

 

Has anyone found a 1/4 mile calculator that takes your diff ratio into consideration? or that can calculate a new time based on different ratios?

I'm thinking one easy way to lower the ET is changing the diff ratio, I remember a mate years ago changed from 2.92 to 3.75 and picked up nearly a second (from memory, it might not have been quite that much.)

The X350 XJR's run 2.87's, but the 3.0L V6's have a 3.31

Any way of estimating the improvement just from swapping the ratio?

BTW most of the calculators I found are, a bit optimistic...

X350 XJR @ 3900lbs (incl driver) with 400HP = 11.9 @ 108mph....

 

X350 XJR @ 3900lbs (incl driver) with 400HP = 11.9 @ 108mph....

That must be with the 45 degree downslope calculator...

 

OK time for a stupid question.

It seems to me that the terminal speed is pretty much dependant on HP alone, give or take a bit for traction off the line. How else would all those calculators keep coming up with same mph for HP results?

But the ET, while dependant on HP too, is more affected by traction and gearing.

Sooo...if the horsepower doesn't change, but you shorten the gearing, you'll find a little more same trap speed, and a quicker ET???

It's an article from 1961 but it talks to me CHEVY'S HOT IMPALA SS

3.36:1 diff, crossed the line in 3rd at 5300rpm, 15.31s @ 94.24mph
4.56:1 diff, crossed the line in 4th at 5300rpm, 14.02s @ 98.14mph

Now, one of the X350 XJR's that have run at Santa Pod in the UK;

RT___1/4et___ mph
.4421 13.9902 104.57
.5971 14.0013 104.72
.6408 14.1308 103.37

I made a quick calculation on the gearing of the X350.
http://dl.dropbox.com/u/11575086/X35...g%20Sheet.xlsx

At 104mph with the stock 2.87 diff they cross the line at ~5600rpm in 3rd

Change to the available 3.31 and assume a little improvement to 108mph, it'll cross the line in 4th at ~5150rpm. That's gotta bring something...

OK maybe not 1.3s like that Impala, but something? Anyone?

 

Can’t speak from experience, but changing the gear ratio will indeed increase the force you put down the wheels. But as the time is shorter, you will not increase hp of course, actually due to the extra friction you will lose a little (not much though).
The late x350 4.2 has a 2.86 rear end and the x150 4.2 a 3.31, so if you find a conv x150 (will be slightly heavier), it would be interesting to see how much of a difference you get there.

 

According to this site Follow-Up Test: 2007 Jaguar XKR Convertible the X150 4.2 S/C Convertible did 13.3s @ 105mph

But that was listed with 420 HP, as opposed to the XJR's 400.

If i've got the diff out to fit the LSD it's a no-brainer to swap the gears as well, just wondering what it'll be worth time wise. Maybe half a second?

Then again this site Jaguar 0-60 Times & Jaguar Quarter Mile Times | Jaguar XJ, XF, XK8 0-60, XJS, XKR S and X Type and 2011 Jag 0 to 60 stats! says a 2005 XJR will do 13 flat, so much BS on the internet...

 

Attached is comparisson pdf taken from the site Automobile-Catalog the complete Catalog of Cars, car specs database

It’s more anecdotal, as you don't have all the specifics/environmentals, and there can be some small differences here and there between the model (so ecu/tcm programming).

But just for fun, even with the small amount of extra hp, and the gear ratio, the 1/4 mile seems here only 0.2 seconds faster.

Here is also an anecdotal site with performance data:
Jaguar XKR lap times and specs - FastestLaps.com

 

Are those numbers from actual tests on a track or just calculated?

Cause it says "ProfessCars™ simulation" and the figures for the XJR seem very optimistic...

13.0 is hard to believe, i've seen the 13.5s given for the X350 XJR a lot more often.

Which somehow lines up with the Santa Pod ET minus the RT...???

 

While avos is right that it does not increase the engines hp or torque what it does do is increase the way the engines hp and torque are multiplied through the drivetrain. So in a sense it does increase it. The trade off is you will now get worse MPG and have more traction problems lol.

Also the x350 comes with a 2.86 rear end ratio and the x308 has a 3.06 but thts not all there is to it also got to look at the transmission ratios the x350 with its 6 speed has a whopping 4.17 first gear where the x308 has a 3.57 first gear. So lets look at this scientifically

Changing the rear end gear to a numerically higher (like going to a 3.31 from the stock 2.86 ) ratio will increase the torque multiplication of the motor, resulting in more rear wheel torque.
Rear-wheel torque equals:
Engine Torque x Transmission Gear Ratio x Rear Differential Gear Ratio

So here goes we will just use the rated engine torque for ea motor

1999 jag xjr

387x3.57x3.06 comes too 4227.6654 of torque multiplication

2004 jag xjr

399x4.17x2.86 comes too a whopping 4758.5538 wow now we are talking now change that rear gear ratio too a 3.31

399x4.17x3.31 wait for it 5507.2773 thts one hell of a jump in rear end torque multiplication

 

Also to note the x350 comes with a curb weight of 3946 and the x308 has a curb weight of 4025 this is also something to think about cus lower the cars weight you will increase the speed, performance, and handling of the car.

 

Also thts some complete BS the stock x350 weighs over 3900 pounds without a driver and so unless said driver is negative weighted and as such takes weight away from car need to be more round 4100 lbs with an average 165 lb man or if your a fatty or weightlifter like me an weight over 200 then even more so.

 

MPG doesn't worry me, if you look in the excel file changing the diff from 2.87 to 3.31 means instead of ~1950rpm at 80mph in sixth it'll be ~2250rpm. Not a big deal.

Yes i've read that a shorter diff can hurt traction off the line (as if the X350 doesn't have traction problems already) however I intend to minimise this with a Quaife LSD, putting 295/30/20's on the rear and killing the CATS.

So if I understand correctly, ratio swap is a good idea then?

 

No dispute that the calculated time was BS.

But I can only go on what Jaguar published in thier own documents;

Kerb Weight of SWB 4.2 S/C = 3671lbs + driver

 

Sorry your right I keep forgetting not all of us live in USA lol and the US version is heavier emissions and safety BS lol

An yes dif change is a great thing I have a 99 camaro with a custom built LS7 427 tht I built with a exo clutch, fully built 6 speed manual trans, carbon fiber driveshaft, and a moser 12 bolt and went from 3.73s too 4.56s and man tht thing was insane couldnt floor it til 3rd gear it would just rip the tires off I had mini tubbed it and put PS2 335/30/19 tires in the rear and didnt help only thing tht worked was my slicks.