Custom SIP GS3 "Streetracer

Created by Alex at 10:02 on February 23, 2023

The engine of the Vespa GS3 is overhauled

"The engine was given a general overhaul. As this project took many years, various parts were added. With the appearance of the QUATTRINI M1XL 172 cc direct intake, it was immediately clear that the GranSport should not only be called that, but also live up to its name in terms of performance. The focus was on an original look and therefore the conversion to a PX engine was out of the question. The housing was welded on, spindled and the cylinder stud bolts were moved. With a suitable connecting rod from Jockey's Boxenstop, in connection with a specially made crank pin, the GS crankshaft was made suitable for a Quattrinita. With the help of an 8 mm thick foot gasket, it was possible to defuse the cylinder a little in terms of the timing. Since the original GS gear ratio is too short, we had a primary gear ratio made by DRT. It fits very well with the engine power and was therefore included in the programme. The clutch also has to cope with the power, so an original Surflex base plate was upgraded with a specially made MMW clutch basket, the 4-disc Malossi linings and standard clutch springs. This clutch copes very well with the power and is also very pleasant to pull.

The 172 is now fuelled by a DELL`ORTO VHST 28 carburettor in matching vintage red. For this, the frame had to be minimally trimmed. The intake manifold did not fare so well. It was completely reworked and the connecting piece between carburettor and diaphragm was manufactured by Jockey's. For the ignition we begged Tino Sacchi to make the Vespatronic suitable for the oldies. So the GS could be equipped with a Vespatronic. Gone is the trouble-prone contact breaker ignition. The exhaust is a PEP 3.0 in the Sport Replica look, adapted to the GS housing. The sound is very pleasant and harmonises wonderfully with the rest of the engine".


Thank you!

"The scooter was then perfectly adjusted by Jockey's Boxenstop and cleared at the TÜV. The 19 hp power is brought to the road with powerful thrust. With this setup, the GS/3 can now keep up with any touring 210 and is also stable.

My big thanks go to Jockey's Boxenstop for the engine tuning, TÜV and the registration service, Stoffi for the paintwork and Markus Wessner for the restoration."

More information, a parts list and exploded views can be found on our Special pages for the Vespa GS3 150.


Alexander Barth is co-founder and managing director of SIP Scootershop. He has been actively driving a Vespa since 1989 and has made his hobby his life's work. Alex was born in 1977 and has 4 children.