I had also mentioned when I dropped the car off, to Nakayama-san, that my car's exhaust stunk. In fact it was overpoweringly bad. Mine's is reporting that this is because the catalytic converter (Apex'i Super Catalyzer) is dead. I suspected this, in fact, and was thinking about getting another one to replace it.
|from Apex'i website - http://www.apexi.co.jp/products/exhaust/cata.html|
The Apex'i replaced the OEM one that was on the car when I bought it. This was a couple of years even before I had the Mine's engine put it, circa early 2006.
At the time, in my research I found that the Apex'i was the best catalytic converter because it had the lowest cell per square inch (cpsi) of only 130 cpsi - most other catalytic converters were in the 200 range (OEM is 400) and therefore more constrictive.
However, I always believed that catalytic converters pretty much lasted the entire life of the car, although now I suspect that is only true if your car is not highly tuned.
But a relief the smell wasn't necessarily caused by the engine. I've asked Mine's to go ahead and install a new catalytic converter - they've recommended an R33 GT-R specific one by HKS, which happens to be the one I was looking at anyway. Hopefully they will have photos of the old one for me to see how badly it had degraded.
The HKS one has 150 psi so a slight increase, however their website claims that their catalyzers have "high purification performance" - so something to look forward to, if true. And if for some reason the HKS fails or dies in the future, at least its replacement cost is not as much as the Apex'i.
In any case, as Mine's has the car for a few more days, I've decided to ask them to do a full check of the car, in order to see if there are any other parts that could be suspect. I'll post what (if anything) they find. Hopefully this whole incident was just a wake up call for me to pay more attention to my car!