CREATE TABLE table_70434 ("Year" FLOAT, "Entrant" TEXT, "Chassis" TEXT, "Engine" TEXT, "Points" FLOAT)

What is the year when kurtis kraft 500f was the chassis?
SELECT SUM("Year") FROM table_70434 WHERE "Chassis" = 'kurtis kraft 500f'
SELECT SUM("Year") FROM "table_70434" WHERE "Chassis" = 'kurtis kraft 500f'