If it's a USA engine, premium is definitely not necessary.
If it's Euro - which I was recently told by "mbdoc" is 9:1 and not 10:1 as I had previously thought - premium-or-not would depend on timing. If it runs without pinging, use regular. If not, use premium.
I was also told by a chevron guy that the same amount of techron is in premium as in regular. Further, I have done the math and to buy cheaper gas and a can of techron is more expensive than buying spendy chevron gas w/techron already in it.

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