There are many possible ways of machining the stock 1.9 liter Opel engine for more power. Many discussions mention upgrading the airflow capacity of the cylinder head with installation of non-Opel parts like Chevy Valves (big valve 1.72" or 1.84" intakes coupled with 1.50" exhausts from V8 engines). This is often combined with installing Chevy pistons (from the 265 or 305 engines), and others advocate stroking the engine by modifying the Opel crankshaft to achieve a 2.4 liter displacement. The lure is lower entry costs, but the obstacle is locating experienced professionals, who understand some of the more theoretical aspects of machining parts that were never intended for use together, to assure proper clearances and heat-expansion tolerances (that were never specified in any Opel service manual). Quality engine machinists who will work on an Opel are a rare breed (and their services are usually priced accordingly).

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