"Nagy" High Compression head for Douglas Rod/G & early Piaggio/ACMA single port engines
Due to the poor fuel quality in the 1940s generally only low compression cylinder heads were used, so as not to endanger the durability of the engines.
Today, ratios up to 1:12 are quite common and durable.
The "Nagy" cylinder head has a moderate increase in compression and with the special geometry of the combustion chamber allow significantly better acceleration, higher top end speed and improved starting.
Your crankshaft should be in good condition before installing the head.
Broken rod bushes or big end bearings are of course even more stressed by the head.
The "Nagy" cylinder head fits all Vespa engine with a raised/straight edged piston (Douglas Rod/G Piaggio V1-30, Hoffmann, ACMA until 1953, 125U). The compression ratio is approx 1: 8.
The "Nagy" head can be installed as a direct replacement for your old head, the original copper gasket must still be used.
It is not necessary to change the carb jetting.
The spark plug must be replaced.a NGK B8HS or equivalent
Also, the ignition timing should be retarded by approx 4 degrees - for example the Dougas Rod standard timing is 33 degrees BTDC, change this to 29 degrees BTDC.