The range value issue of 0 to 255 that you are having is because of the pixel type being set to 8_BIT. TO have higher numbers set a higher bit value.
From ArcMap Tool Help
1_BIT —A 1-bit unsigned integer. The values can be 0 or 1.
2_BIT —A 2-bit unsigned integer. The values supported can be from 0 to
3.
4_BIT —A 4-bit unsigned integer. The values supported can be from 0 to
15.
8_BIT_UNSIGNED —An unsigned 8-bit data type. The values supported can
be from 0 to 255.
8_BIT_SIGNED —A signed 8-bit data type. The values supported can be
from -128 to 127.
16_BIT_UNSIGNED —A 16-bit unsigned data type. The values can range
from 0 to 65,535.
16_BIT_SIGNED —A 16-bit signed data type. The values can range from
-32,768 to 32,767.
32_BIT_UNSIGNED —A 32-bit unsigned data type. The values can range
from 0 to 4,294,967,295.
32_BIT_SIGNED —A 32-bit signed data type. The values can range from
-2,147,483,648 to 2,147,483,647.
32_BIT_FLOAT —A 32-bit data type supporting decimals.
64_BIT —A 64-bit data type supporting decimals.