I currently have an 05 str. I plan on possibly picking up an 09 xf supercharged even though i really want a 2010(can't justify spending 30k+ on a car at this age) I see eurocharged has been making nice gains with the 5.0 pulley and tune. Has there been gains similar in the 4.2. I really want the car to at least run high 12s

 

There is no data. All the tunes thus far have been with the 5.0 I have a 4.2 but I have not pulled the trigger yet. I'm looking at getting a pulley first.

 

Amgeater, the 09 has the same engine as our STRs but a much better dual intake. I also believe it has vvt, but I am unsure what that does or peak power. 13.6 is very fast, but I think you have some further sorting to do with your current STR before you switch to an XFR to fix whatever might not be working.

 

Yea I kno its the same engine. But was woundering with the tune how much power have they been making since they seem to have proven tunes. My car has 99k miles and plan on picking something up with lower miles, I really love the look of the xf and if I wanted all out speed I would just pick up an e55 or 335i coupe and mod them. While spending a lot less money.

 

Not many have posted dynos for the SC 09. I put together a intake kit which I'm extremely happy with. I'll probably swap to the smaller upper pulley early next year and get a dyno at that time. I don't think I'd drop the money on a tune without a lot of data to back it up.

 

I see they trap 106-108mph which proves it has a little more power than an str. If a pulley tune and exhaust can make the car trap 4mph higher it would easily put the car in the mid 12 range.

 

Bear in mind that an XF is substantially more aerodynamic than an S type, affording improvements in both mileage and speed with the same engine power.

 

Not true. Aerodynamics only come into play as you reach triple digits (c of d is ^2) especially if the difference between the two is a measly .02 (XFR is .29 and STR is .31). Aero affects top speed, but definitely not 0-60 and cruising on the highway.

 

After doing done research, I think the reason why the 4.2 XFR is quicker than the STR simply has to do with it redlining each gear. Not sure if the 09 got the active diff that the 5.0 R gets, but if it's the same, then we have out answer. +20 peak hp negated by an extra 200 lbs plus redlining each gear plus an active diff for better launches, is probably what it comes down to, not to mention most STRs are starting to see higher miles being that the 03's are over 10 years old.

 

As far as I know the 09 XF Supercharged did NOT get the electronic diff.

 

There are some differences that can explain the advantage of the xfr. The final drive ratio of the str is 2.87 compared to 3.31 for the xfr, and of course the latter has about 20 hp more (due to double air intake, and possibly vvt).