Here In Rocky Mountain House, we have a Co-op gas bar. I have asked them a few times about their fuel. They are not sure about where it is from, or who makes it (the same truck delivers to Shell here). So I deferred to Esso, The 5.0 Mustang does like it so far. The engine does feel a little bit softer now then when I used Shell, But the smell is gone.

Yes I know all about the octane to power factors (better then most). Yes the lower the octane the more energy. But if the engine is built for the higher octane it will back off the timing (making less power).

On a side note: I did get an engine light flashing three times with the Shell fuel, but never with Esso. The MIL never stayed on or recorded a code.