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My Carrera requires premium. I don't know about the SC.
From what I have read don't torque the head studs. That often is the cause of them breaking. If they are not loose and broken, leave them alone.
It does sound like detonation my be your problem. Back when my original engine in the El Camino was past 250,000 miles it would ping under load with regular. I had to run the middle grade just to keep it from detonating. When I took it apart after 301,000 miles it had just little bits of carbon on top of the pistons. I guess it was enough to raise the compression and cause pinging.
My suggestion is ren a few tanks of premium and see if the noise goes away. Then change back to the regular. If the noise comes back, you know the problem.
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Glen
49 Year member of the Porsche Club of America
1985 911 Carrera; 2017 Macan
1986 El Camino with Fuel Injected 350 Crate Engine
My Motto: I will never be too old to have a happy childhood!
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