I just got done having my engine built by my tuner. I lowered my compression ratio to 10.0:1. The oil viscosity I was recommended to use is 5W-30.
I've spent quite a few hours (during the last couple weeks) reading many forms on what company and type of oil I should use.
Honestly, to each their own. I chose an oil that was still top end but affordable and easy to find. I was thinking about Motul and AMSOIL but I believe Mobil1 is on par; statistics can say a lot but it really depends on the application, your setup, etc. Unless you are a serious drag racer with the engine built like the shit you'll do just fine with OEM oil. Built engines and forced induction engines could uses a thicker oil to keep the temps down. Studies show that changing the viscosity can change your HP output and fuel economy; but honestly, I don't think 10HP is that big of a deal with an FI engine. Stock, you can make it up with a different exhaust, lighter engine pullys, and hitting the gym (just kidd'n on the last one lol). Also, consider the area and the temperatures. This can help with the viscosity decision. Again,
to each their own.
Personally, I like to do more frequent oil changes so cost analysis is important. Walmart sells their Mobil1 oil (5qts) for around $25. All the auto parts stores sell it for about $38 in my town. I got them to pricematch walmart and bought three.
Sources and Good Reads (from form members):
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http://www.mobiloil.com/USA-English/...duct_Guide.pdf
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http://www.lubrizol.com/EngineOilAdd...l/default.html
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http://www.machinerylubrication.com/...iscosity-index
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