The original question was, should the OP run higher viscosity oil like 5W-50 when the OE spec was 5W-20. There were a bunch of different answers from different members which is confusing. Some say just use 5W-20 and go with a high end mPAO based oil, other say user a higher viscosity oil like 5W-50 because that's what the Boss 302 uses. Who is correct or who has the more ideal answer...when I saw this thread I thought to myself, well holy crap, I went through that same ordeal, but instead of relying on other's opinions and anecdotal "logic", I started a research project to find real test data to substantiate or invalid these claims. What I found was simple, OE low viscosity oil specifications are perfectly fine for street car applications under most street use conditions. But there are different specifications based on the car's design intent. The Boss 302, GT350 and Ford GT are track focused street cars, consequently they are set up that way. The OP's 2011 is NOT. Hence the 5W-20 oil specification. The question then becomes, what oil is better suited for that car because it is 1. no longer stock and 2. being used in a way it was never intended to be used when Ford designed and tested it. That means in order to provide the most valid answer possible, we should look at the engine design and it's supporting systems to get a good idea of how oil viscosity impacts their performance. 1. Oil pump pressure and oil volume of flow 2. Rod and Main bearing clearances 3. Cam phasor response 4. Hydraulic Lifter function 5. Oil cooling jet operation. How do we get that information? Since it's difficult if not impossible to find the exact test data from Ford, the next best thing is to look at published information from Ford's part suppliers which is Borg Warner, Clevite etc. who publish data on their specific systems capabilities. That's all I've done is look at each of those systems to determine the best starting point for the OP, I did it for myself for the very same reason. That's why if you look at some of my posts, there are document attachments on several of them to back up my claims on how it impacts each system based on OE supplier testing and data which not a single person has provided in this thread...yet we are still debating everyone's opinions on the matter, each which differ. I guess people will do what ever they want regardless of reality. Best of luck with that. To the OP, look at the data and make a decision for yourself. To the best of my ability, based on all of the information I have collected, 30 and 40 weights are ideal for performance street car applications in the actual base stocks and additive packages available on the market. The current offerings of 5W-50 from MotorCraft and Mobil 1 (not sure how Lucas Oil's 5W-50 holds up) use sub-par group III base stocks that shear down to 30 and 40 weights which includes loss of HTHS viscosity, so they are more viscous than necessary during street use when new, but do not provide additional protection under track conditions for very long and I've seen UOA's showing them loose up to 36% of their viscosity, which is two grades lower. It's not optimal for your 2011 Non-track pack GT. Stay with high quality base stocks, mPAO, GTL and Esters. Any of them are highly shear resistant and generally come with great additive packages that promote low friction and wear rates while keeping drag losses to a minimum. Best of luck.