I got BLOWN away from my friends S63 and my other friends S430 I had trouble with...

Going 120-130 i saw the S63 weave thru traffic and just charged by me like I was standing still, not cool.

Need that power...

 

Don't race to those speeds. Also, he's got better gears and far
superior aero. Cut off the race at 100mph, you become exponentially
slower than them at those speeds over 100. If you are having trouble
with an S430, your car may not be running properly, I have toasted
a 135i, Camaro SS 6spd man on the track and they cannot keep up
up till 100-110. Our engine has good top-end, but you also have tons
of drag. An E39 M5 (also on the track) was dead even with me from
50-90 or so, but if we went faster he would've killed me. (not that
long of straights) that car does 0-100 in 30.0s, compared to the XJR in
52.7s. That's aerodynamics mainly.

Speeds to roll on: 0mph (this car on sticky tires hooks better than most
cars) 15mph (city speed) the car downshifts to 1st and a turbo car
will lag and get destroyed. 40mph is not good, you are only making about
300hp at that RPM in 2nd gear. 50mph is the roll-on speed you want.

 

Maybe you need a tune-up on a rolling road first to check your own car is putting out the expected power.

Merc S63 is a bare-knuckle brawler & the UK car mag Autocar described it's straight-line performance as 'Titanic'. Then again, it packs over 100+ bhp more than the XJR & the latest version has 7 gears & well over 500bhp, so even the trusty old XJR wouldn't have much of a chance against one of these driven in anger...

 

I expected to lose to the S63... just didnt like it watching him come from 50 yards back and blowing by me.

the Twin Screw would more than make up for the gearing advantage it has over me i'm thinking.

 

Well, the twin screw installation thread for the XK8 just finished. You can continue carrying the torch with your own twin screw install.