Dan Thompson wrote:

Personally, I'd say the placard is all you need, but only if you are sure
the STC for a plane like yours is just a paper whipping excercise.

Even if the STC for your aircraft is just a "paper-whipping" exercise, beware that
the STC on many of these aircraft specifies a minimum operational rpm level. It may
be OK to dump mogas in a Cessna 150 (to pick an example) without actually springing
for the SCT, and it may not. Unfortunately, I no longer remember the rpm level for
that plane, but my A&P had to adjust the carb a tad when I bought the STC.

George Patterson
This marriage is off to a shaky start. The groom just asked the band to
play "Your cheatin' heart", and the bride just requested "Don't come home
a'drinkin' with lovin' on your mind".