I did not do anything other than install a cat delete pipe and do the procedure that recalibrates the computer, and my RT ran very nice. I did the same thing when I replaced the stock system with the exhaust I have on now, shown in an earlier post in a video trying to show the sound of it. I never noticed any actual gains or losses by doing this, but I do have better gas mileage than when it was stock. I can get around 45 mpg if I behave myself, and while I know of no dyno's that will give me a performance graph, seat of the pants says I can hit the rev limiter (8200 rpm) in low and second gear with no drop off in power (IE: it feels very linear ). Some one asked about proper shift points earlier, and that is a difficult question to answer, because it really depends on how you drive, and what you are looking for. I'm used to torquey engines and because of that I tend to short shift (shift early) and my RT seems happy to shift at 2,000 rpm as long as I'm not it a hurry, and I tend to get the 45 mpg number when I don't race around over 3,500 rpm. But my RT with the 1330 engine will shift and cruise, just about anywhere I want to. You can tell if the rpm is too low, because you can feel the vibration or shudder thru the seat of your pants, the rpm too high is almost impossible because of the rev limiter, but red line on the tach is around 7,800 or 8,000 rpm if you go by the change in the thickness of the while line that is on the face of tach showing the rpm. Hope this helps some of you out, or at least gives you another way to look at things. I'm an old guy, and have done a lot of racing ( cars, trucks, go karts and motorcycles,) on road and off, and you can take what if said or not, just enjoy your Spyder, I know I do.
David