Cylinder head Polini Racing for 133cc Vespa V50, ET3, SS50, SS90

With appearance of the Polini Evolution cylinder kits at the scene, the cast iron barrels got updated as well. From then on the Polini cast iron barrel is labeled as Polini 133cc Racing. The most innovative feature is the new Polini 133 Racing cylinder head. A massive head with enlarged cooling fin area, CNC machined combustion chamber and copper head gasket.

Thank to the massive (anti-warp) thickness and the new head gasket design leaking heads are an issue of the past. At least if the head nuts are tigthened down properly.

The head is offered by Polini as an upgrade for all Polini 133cc kits as well. We will have a closer look if it is worth it. Longer cylinder studs are already included into the delivery of the head. Our recommended head nuts are those from Naraku.

The better cooling efficiency of the head gives room for a higher compression ratio.

With a burette we check the combustion chamber volume.

Compared to the old head with it’s 16.8ccm, the new head has 15.99ccm. This gives a higher compression ratio of 9.1:1 instead of the old 8,7:1.

The head gasket volume we have considered too. We used grease to simulate this.

The slightly higher compression ratio combined with the new combustion chamber area gives higher horsepower as well as torque readings. The better thermal absorption of the head gives the same reliabilty as on the lower compression head. At least if carb and ignition settings are properly done.

Once you have taken of the barrel, head or replaced any cylinder head or base gasket, you should always check the squish clearance of the top end. Depending on the specific engine setup. it might be a good idea to adjust the ignition timing too. With higher compression ratios it might be a good idea to reduce the ignition timing (=use a firing point closer to TDC).

The new Polini head is a nice and up to date improvement for the Polini 133cc kits. A good idea for all Class 5 racers at the ESC.