M1 specifically has overly thin 30wts. almost any other 30wt. is OK and an impovement.

 

....and to think the c5 vettes come with a recomendation of Mobil 1 5w30 on the fill cap, you think they would research that sort of stuff....

 

I run a K&n 3002 filter oil I change every 1000 miles. Just with the engine brake in. It's done braking in I use rolal purple or red line, amoil. The filter holds more oil then the stock. More oil is always good ..

 

Gets it past warranty that is what counts. Sounds as if you don't believe me, go to the oil board link and look up so LT1 oil analysis results, they clearly show that M1 30wts. result in higher than necessary bearing wear metal numbers. To me that speaks much more about an oil than the marketting/CAFE crap that resulted in 5w-30 being factory fill in the Vette. The Vette needed synthetic, 5w-30 was to be the choice due to CAFE, and M1 was the brand for marketting and supply reasons, NOT because it was the best for the application. Besides even if it was the best 10+ years ago the synthetic market has expanded greatly in that time period and formulas change as TIME and actual use teach manufacturers about real work results.

 

Like many things on street cars, it is a compromise. The light the oil, the better the efficiency. It might seem minute, but companies pay attention. Ever seen the phrase "Energy Conserving" stamped on the oil bottle or fill cap? I've seen a recommendation of 5w20 on some of the newer Ford trucks!!! 5w30 is in my opinion too thin of an oil for the LT1, but the flipside is that some people use oil that's way too think. 15w50 is, in my opinion, too thick. Sure it will protect, but there comes a point when you start losing power by having to pump that thick oil throughout the motor.

Anyway, there are lots of choices out there, and many of them would be very good for use in the LT1.