2013 C207 (M276) and "Top Tier" Gas.
OK, I wasn't drinking or hallucinating, but I swear I heard a change in the exhaust note after filling up with a "Top Tier" gas (Marathon)
Wishful thinking? Actual occurance?
Opinions welcome....

What fuel and octane grade had you been using?

Circle K (Southeastern US) Premium 93 octane

Wishful thinking (lol) -- must have been echoing off the tractor trailer parked over at the diesel island.

But also - at 3/4 throttle, exhaust note down an octave, less thrashy sounding and "smoother". But then, it lives its life at 1/3 of the rev range.
I did notice on a 250 mile trek in I95 last week that it ran~100 rpm lower at 75mph than used to.... just at 2000.
Again, not imagining?

Mine drinks 91.. must be an additive thing.

I believe you when you say you think you noticed a change. Happens to me all the time, i'll be driving and think to myself my car seems to be running great today.

You do mention driving a certain way, 1/3rd RPM, then that day you were at 3/4 throttle.

I cant see 1 fill-up really doing much though. From my understanding the Top Tier label just means an increased amount of detergents and it has to be used consistently to see the benefits.

I typically get gas at Mobil, Gulf or the Stop & Shop near my house. I get 93 octane since most gas stations have 87, 89 and 93. Theres a Sunoco that has 91 but they are a rip off and usually charge $1/gallon more than everyone else. I have always added a bottle of Techron in the gas tank once or twice a year for 20yrs now in all my cars. More recently starting last year I will add 1-2oz every other fill-up and the engine seems to be running great with over 150,000 miles on it. I do this because I dont think Gulf or Stop & Shop is listed as Top Tier so I figure add a small amount of Techron. The Napa auto parts near me usually has the 32oz bottle of Techron on sale for around $10.50.

I agree, its early in the test and maybe it's wishful thinking.... better eval after a few tankfulls :-)