CREATE TABLE table_15471 ("Year" FLOAT, "Team" TEXT, "Chassis" TEXT, "Engine" TEXT, "Points" FLOAT)

What year did the Cosworth v8 engine participate in?
SELECT AVG("Year") FROM table_15471 WHERE "Engine" = 'cosworth v8'
SELECT AVG("Year") FROM "table_15471" WHERE "Engine" = 'cosworth v8'