The twin-turbo came with the car when I bought it used. Performance wise, the best I have gotten out of it is 6.7 sec. 0-60mph and an estimated 270hp using a G-Tech accelerometer.
The car hasn't been shaken out (when I got it there was a BMW airbox before the intercooler!!) and I'm sure there is more performance to be had. I don't have all the right tools or knowledge and am still trying to figure out the secondary injector system (so it doesn't lean out). Proper tuning will take reinstallation of an O2 sensor and fuel mixture gauge (to monitor spent gases).
The other option is a TEC II injection system, but electronic fuel injectors need to be added to replace the mechanical injection system.
Unfortunately, it's become a "toy for free time" and free time hasn't been existant.
85 300E euro-spec., twin-turbo AMG aero kit
89 300CE AMG aero kit