The 450 SX is a single cylinder 4 stroke, so no you do not mix gas.
That's something you need to check with a qualified KTM shop about.
KTM recommends Motorex Power Synt 4T 10W50
ktm 450 sx
Got this off of KTM talk, 44HP for a 450 exc.
1.35 L
The KTM sx is fast but the yfz is the best for what I do, what kind of riding do you do?
A 450 shoud be 90 to mid 90s
YFZ 450 WILL SMOKE It
The 2004 ktm 450 EXC has 48Hp
around 80
ktm 450sxf
Seat height on the 2010 450 SX-F is 38.78 inches