| Industrial engines. They are still used by several | | | | on this engine are interchangeable with the Polini. |
| manufacturers (most notably Blata on their entry | | | | What's the difference between the 'series I' and |
| level bike) and typically produce between 2.5 and 3.5 | | | | 'series II' crankcase?. Fuel is drawn from the carb into |
| horse power (hp). All are air-cooled. Tuning and | | | | the crankcase via a one-way valve known as the |
| performance parts are very limited. | | | | 'reed valve'. The intake port (where the reed valve |
| The Chinese 47/49cc. These engines are used in the | | | | and carb join the engine) on the series I engine will |
| Chinese made mk2, and mk3 minimotos. They are air | | | | only accommodate a reed valve assembly with one |
| cooled and produce between 2.5 and 3.5 horse | | | | reed 'petal' whereas the series II will take a reed |
| power (hp). This engine is different from the industrial | | | | valve 'cage' that accommodates two reed petals. A |
| engine that is used in the Blata, as it is specifically | | | | two-petal reed valve will allow more fuel mixture to |
| created for mini moto use. | | | | flow into the engine and, therefore, produces more |
| Polini 4.2 engine. This is the basic Polini engine and, as | | | | power. |
| its name suggests, it produces 4.2 hp in standard | | | | Polini Super engine. The super also uses the series |
| form. It is air-cooled and uses the 'series I' crankcase | | | | two crankcase but with a 5-port cylinder. It is only |
| with the 3-port cylinder. There is plenty of scope and | | | | available in water cooled now but used to come as |
| parts for tuning but few people bother because | | | | air cooled as well. To compete with Polini, Mallossi |
| most racing classes for the 4.2 won't allow any | | | | manufacture an alternative 5-port cylinder. There are |
| modifications. | | | | no restrictions on tuning supers and with engine |
| Polini 6.2 engine. The top end of this engine is the | | | | 'porting', bigger carbs and other performance parts |
| same as the 4.2 (3-port) but is available with either | | | | they can be turned into awesome machines (for their |
| water or air-cooling. The bottom end uses the 'series | | | | size) easily producing 12hp. |
| II' crankcase. This helps to make it more powerful. | | | | What is meant by 3 and 5 port?. This refers to the |
| Race regulations don't allow modification to the | | | | amount of 'transfer' ports built into the cylinder. The |
| engine internals but do allow performance parts, the | | | | transfer ports draw the fuel mixture up from the |
| most significant being the exhaust. There are a wide | | | | crankcase and 'dump' it above the piston prior to |
| range of alternative exhausts that year after year | | | | ignition. A five-port cylinder has potential to produce |
| manage to extract more power from the engine. | | | | more power. |
| Consequently the 6.2 'tag' no longer means anything, | | | | 40cc or 50cc. The 3 port engines are only available in |
| these little rockets (more often referred to as | | | | 40cc. The 5 port cylinder comes in both 40 and 50cc. |
| 'production' nowadays) claim power outputs of up to | | | | ZPF offer a tuned 5-port polini cylinder with their own |
| 9hp. | | | | 'special' cylinder head. The extra cc gives 25% more |
| The Chinese made water cooled engine. This engine | | | | displacement and, therefore, has the potential for |
| is very similar to the Polini 6.2 however it is a series 1 | | | | more power. 50's are more common in the USA but |
| crankcase engine. The engine is water cooled and is | | | | they're catching on fast in the UK. The UK now |
| used in the Origami B1 replica. The engine produces | | | | allows them to race in championships. |
| around 7.5/8.5 horse power (hp) Many of the parts | | | | |