What start has a ford cosworth dfx as the engine, a year later than 1981, and kraco enterprises as the entrant?
CREATE TABLE "indianapolis_500" (
  "year" real,
  "chassis" text,
  "engine" text,
  "start" real,
  "finish" real,
  "entrant" text
);
SELECT "start" FROM "indianapolis_500" WHERE "engine"='ford cosworth dfx' AND "year">1981 AND "entrant"='kraco enterprises';