This excellent article is from our friends over at Forced Performance. It is written for 4G63 owners, but it 100% applies to all CT series upgrades. We use Valvoline VR-1 Race oil in all of our personal MR2's. http://store.forcedperformance.net/merchant2/graphics/news/Forced%20Performance%20Recommendations%20for%20Motor%20Oil.pdf So for the cliffs notes crowd out there, here is the summary: Do not use Mobil1 10w30 or any other “on highway” GF-4 oil in your 4G63 motor with any high output stock appearing turbo. Use a suitable racing oil designed for high film strength and heavy pressure loading such as Brad Penn, Joe Gibbs, Valvoline VR1, Amsoil Racing oil or Royal Purple racing oil. Also remember that racing oils are detergent free and need to be changed frequently. (I need to add a note that not all Royal Purple or Amsoil oils offer race level protection)