One problem I had with the muffler was that it touched the black plastic 'thing' that's attached to the bottom of the stock bumper. It was only a matter of time before I noticed melted plastic on the left side of the tailpipe. One would be advised to carve out the part that may come in contact with the pipe end.
Another thing that happened was that I started to hear rattling from around the muffler. It turns out part of the muffler 'box' was nearer to the foil-like metallic shroud that would originally wrap nicely around the stock box. It's bendable so the problem was solved right there.
I've been more than happy with the increased torque since. Being a wuss, I've kept the boost pressure set to 0.76, which is lower than how high the stock systems go. It's a boost-down version faster than when it was in stock condition. Occasionally I'll raise it to 0.9, just for the fun of it. I think I'll raise it little by little as I get inocculated to the power.
In the meantime, I had been to some circuit runs but didn't know how fast I was going because I still had the stock speedometer. In Japan that means up to 180 or 190, kph that is. At Fuji Speedway(FISCO), in the final straight I remember getting up to 6000rpm on 5th gear. Since it's roughly 110kph at 3000rpm on the same gear, I calculated that I was going about 220kph. I'd brake to prepare for the first corner. Thereafter, when I glanced at the meter to make sure I'd slowed down enough, sure enough the center meter was moving counter-clockwise, but the speedometer was stopped at 4 o'clock for what seemed to be a couple seconds. Hopefully by the time I glanced again it was moving.
I had an expensive choice of either getting the whole assembly by some shop with the full-scale reading or to just have the speedometer surface replaced with something adjusted in the back. I chose the latter. The former would have reset the overall odometer reading to zero. Now, if I were selling a car maybe a smaller number is advantageous but I wasn't and do not intend to sell my car. But for myself I wanted to keep recording how much I've been running with it overall. Unfortunately, I haven't had a chance to go to FISCO since then to actually see it. I am told that people get to roughly 250kph before braking. That's a scary corner for the uninitiated.
About half a year later, I had the flywheel, clutch plate and cover changed. I did not opt for the double nor triple plate because I didn't feel it was necessary. I still don't. One problem I had was with the clutch hose. If I remember correctly, it shares the fluid with the brake system. That hose extends to the firewall near the ABS box (to the right of the serial number in right-hand drives). I've heard of many cars with the same problem after 2 or 3 years. I had the hose changed to a stainless one. Problem solved.
Although stock, the original suspension actually did quite well with the increase in power and balance was not compromised. It did eventually start feeling softer at turns so I had them changed. After installation the car was about 1/2 inch lower than it was before. Remember that the original one does lower little by little with use. This was when I began learning how to turn onto slopes and grades without scraping the lip of the stock front bumper.