What a difference. I didn't think it would be that big a difference.
The tuning company I used is running a special this month (March 2011) so I was already on the fence about getting this done, and when I saw this sale/promotion, I jumped on it.
It was just completed literally a few minutes ago, and I took it out for a test drive. I have to say that it was dangerous at first - the added torque in the low end in conjunction with the increased pedal sensitivity settings made me literally peel-out-of-my-driveway just now. I felt bad, kids were playing around on their bikes and parents were watching
Anyway, back to the tuning:
IMHO it was money well spent. The tuning did a number of things, and took 30 minutes or so via remote. They send you a cable that is a special USB to ODB2 when you buy this package. Then you set up an appointment with them for a remote tune. You tell them what mods you have (if any) that they can dial in. My car is stock completely, so it made it very easy. The car's ECU got flashed through the cable, they called me back when it was complete and told me to take it for a test drive, and call them back to make sure I was happy with everything.
I'm not sure if they have any tuning programs for the R171 but mine being the big brother to the Crossfire and SRT-6, shares the same tuning program.
So all I can say for sure is if you have a SLK32 or SLK320 they have a tuning program for it.
I'm copying the link over from Crossfireforum.org for those interested. I'm not trying to promote them or anything, I just wanted to share what I did for those who might be interested in this promotion.
Regular price I believe is $399 for the tune, and $100 for the cable alone.
This promotion they have is $265 for the tune + the cable.
It takes some getting used to with the throttle as sensitive as it is, but it is definitely more fun to drive now!
They say about 20hp/20 torque gain and I do believe them after the test drive. I tried to factor in the pedal position change to make sure I wasn't being biased. It shifts better, holds the gears better, among other things I've noticed. And my Dunlop Direzza's are no longer able to keep grip when accelerating most of the time now.