Minimal maximum byte for Turing Completeness
Haskell, score 61 (=)
Characters used: !#$%&amp;()=
The SKI combinator calculus can be implemented in Haskell with nothing but basic function definition, using !#%&amp; as identifiers. Infix function application $ is used to save on parentheses and strip down one character from both S and fix. Finally, K only takes two arguments and can be more shortly defined as an infix operator.
S combinator: s x y z = x z (y z)
(!)(#)(%)(&amp;)=(#)(&amp;)$(%)(&amp;)

K combinator: k x y = x
(!)#($)=(!)

fix combinator: fix f = f (fix f)
(&amp;)(!)=(!)$(&amp;)(!)

Since Haskell is a strongly typed language, the fixed-point combinator fix is needed in order to make (typed) combinatory logic Turing-complete.
The I combinator is not strictly required since it is extensionally equivalent to SKK, but it can be defined as (*)(!)=(!).
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