I have put about 2000 miles on my 95 sc400 and have never seen a hint of smoke. I normally drive 7 miles to work and back and am normally a conservitive driver. However I took a 300 mile tpip to visit my dad last weekend and on one staightaway hit 100 mph, then the next day i tached the car to 5700 rpm twice, the next morning when i started it up it puffed gray smoke i hit the gas a couple of times and it still smoked. I drove back home and started it the next morning and you couldnt see any smoke, i am wondering about the cat. converters at 119,700.