Hi
I also have a 4C with rear bumper delete. My car runs 315/30-18 rear tyres on 18x12 et0 wheels from Forgeline Usa.
I would like to know how you have increase your wheelbase.
To get more power, we will need a better turbo. There are so many fake claims but I doubt that I have more than 280BPh despite
downpipe cat delete, K&N inlet, straight out exhaust, stage2 comp tune. I have managed to loose about 70Kg off lying factory figure of 925Kg. I weighed every bit I removed and 910Kg now on scales.
Cheers Mat