I agree that
Amsoil is a little overpriced, but it IS a very good product. I honestly think that Mobil 1 is just as good though. A good rule of thumb is that you shouldn't switch to
synthetic oil (if you've been using conventional) if you have over 60k miles. I used to have a copy of a comprehensive study of thermal breakdown and life spans of
oil, but i don't have it anymore. However, the authors conclusion was that Red Line made the best
oil overall, Mobil 1 was the best value, and Valvoline Max Life was the best conventional oil. One of the worst was Royal Purple. It significantly lost viscosity after about 1000 miles. I think Mobil 1 changed their formula pretty recently, so I think there's some debate as to whether it changed for better or worse.
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under construction: FFR 1445k, svo 302, inglese intake, coil overs, four wheel disk brakes, stewart-warner gauges, etc., etc....