My friend with a stock SType R and I dragged a few times last night after work. We raced a little over a 1/4 mile. I'm happy I won the 3 times but barely a full car length. Hell if I didn't have the exhaust mod and filter would I even won at all?!*

My car is in top condition, great tires, etc.. I had a 1/4 tank of gas no passenger. He had a passenger and his gas was about the same. I really thought I'll beat him a lil more convincingly. I know... same engine and tranny... I know... but still! I'm also aware that the Silverstone and earlier 4.0 are a couple tenths faster because of the couple hundred pounds added to the 4.2 cars. I've seen times of 12.9 - 13.2 posted for these from the mags and 13.0- 13.4 posted for the 4.2 with the str having 13.3 to 13.6.... if it was the 4.2 XJR I would not be surprised if I lost with its light weight aluminum body.

I need to get a lower pulley for xmas and go get him again. I may go for some custom magna flow hi-perf cats. What else can I do without breaking the bank? I'm only trying to have a 12.6 2005 XKR.* I notice a lot of more performance tuning is done here with the STR vs my fellow XKR guys... help ya brother out!

Juk

 

STR'S kick *** ; ) tell him to get the pulley and air intake... that way you can get a good look at the boot on the STR as it passes you

 

gotta get me a lower pulley for sure if it's gonna make a big difference.

Are there any true 12.5 to 12.7 sec STR or XKR?

 

You get some nice low rev power and torque, but it does not make any big improvment for your 1/4mile time. 4.2 has already 160mm lower pulley ( 4.0: 150mm ) so the difference is not too big with 169-177mm pulley. Better intake tube lowers vacuum and gives good results with small money. Next steps maybe boring out the TB, bigger MAF and water/methanol injection. All these 4.0/4.2 XJRs, XKRs and 4.2 STRs are 13.4-13.8 cars as stock. It's easy to go down to low 13s, but 12.6 needs more than just changing few parts. Quickest STRs here have run 12.9.
Good luck.

 

Low to mid 13s is what the cars run anyway. 13.8 is kinda slow for these cats. From all publications and etc we on average should have a 13.4 car. Now my lil dream is crushed XJR99

Hey on the quickest STRs what mods are running?

 

If you have a few (thousand) bucks, revive your dream. Check this:

https://www.jaguarforums.com/forum/p...xtra-hp-42059/

As I understand it, the twin-screw upgrade is available for the XKR, but not yet for the STR.

 

I was talking about range for stock 4.0 + 4.2 cars. 13.8-13.9 is typhical for stock 4.0 XJR with average conditions/driver and normal street tires.

Here forum 1/4mile standings. You can see few modified STRs there, but no 4.2 XKRs. I am sure as stock you run 13.4-13.5 and down from the level you need about 10-11bhp per each .1 and specially in the range of 4000-6000rpm where you are on second and third gear.

https://www.jaguarforums.com/forum/m...andings-84783/

 

Thanks! I'll certainly check this out

 

Boring out the TB doesn't give much in the way of size or power :/