user: Question: What chassis did the Porsche Flat-4 use before 1958?
Columns: ['Year', 'Entrant', 'Chassis', 'Engine', 'Points']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1953.0, 'Rennkollektiv EMW', 'EMW', 'EMW Straight-6', 0.0]
SQL:

assistant: SELECT "Chassis" FROM "Table" WHERE "Engine" = 'Porsche Flat-4' AND "Year" < 1958.0;