Since we discuss this so much on the forums Im making this review to help people decide on a good choice for motor oil. I ran Penzoil in my Rex when first got it as that was what the dealer used, car ran normal nothing special. On my oil change I switched to Royal Purple... pure crap. The Rex idled harder and ran harsher, huge difference. So I ordered Amsoil Signature Series from Jordan based on everyones recommendations. When I drained the Royal Purple it was already broke down and nasty after only 1200 miles. After 340 miles of Amsoil I noticed a significant improvement, the car idles and runs so much more smoothly which seems to get better. At 500 miles I noticed a small fuel mileage improvement also. Now Im not trying to say that royal purple is terrible for all cars (my roommate runs it in his built Cobra w/no problems) but I would not recommend it for a turbo'd car, just runs like shit. It cant handle the higher temps.