Vespa Tuning for PK 50 S-XL2 / V50
For the tuning of a Vespa PK 50 or Vespa 50, there are numerous possibilities. This article provides an overview of the wide range of tuning parts, their effectiveness, and explains how original Vespa engines can be enhanced.
It covers the areas of cylinder, carburetor, racing crankshaft, primary drive, and racing exhaust, and also explains tuning engine casings and cylinders through milling work. The article is specifically focused on tuning for the 75cc class, which represents the first major stage. The insights gained are of course applicable to higher displacement classes as well.
It should be noted that the operating permit expires as soon as performance-enhancing tuning measures are carried out.
The different areas of Vespa tuning
- Tuning cylinder
- Adaptation of the channels
- Timing
- Racing crankshaft
- Carburetor
- Exhaust
- Increase top speed
Tuning cylinder
The first step in Vespa tuning is the change of cylinder. A larger cylinder with more displacement makes a noticeably significant difference, and the price-performance ratio is very good for the increased performance gained. The original 50cc cylinders of the classic Vespa V50 and PK engines cannot be compared with modern engine concepts, which can generate significant additional power even with 50cc through channel processing alone. The recommendation for Vespa V50 and PK 50 Smallframe scooters goes as the first measure clearly towards performance enhancement through increased displacement, where only the combination of good workmanship, a good piston, more torque due to more displacement, good channel design, and matching timing lead to the desired performance increase.
The increased bore diameter provides more surface area for the mixture exploding in the combustion chamber to act upon. As a result, the piston with the larger bore diameter also transfers more torque to the crankshaft. More torque is the basis for higher engine power, which can be further influenced by machining the cylinder channels. Only where there is torque can power develop later. The torque curve can be influenced by modifications to the timing, ultimately allowing the characteristics of an engine to be changed.
List of available 75cc cylinders for Vespa V50 and PK 50 S-XL2
- RMS 75 cylinder with 3 transfer ports
- DR 75 tuning cylinder with 3 transfer ports
- DR 75 tuning cylinder with 6 transfer ports
- DR 75 Formula tuning cylinder with 10 transfer ports
- Olympia 75 tuning cylinder with 6 transfer ports
- Polini 75 tuning cylinder
- Polini HP4 cylinder 75cc
- Malossi 75 tuning cylinder
- Pinasco 75 cylinder
- for manual transmission
- for Vespa PK50 automatic
RMS 75 cylinder with 6 transfer ports
The RMS 75 cylinder is one of the cheapest options for getting into Vespa tuning. The quality and workmanship are sufficient in the sense that the cylinder set can be driven reliably. It is advisable to rework all edges with a small finger file. The scope of delivery is complete except for the studs for the exhaust.
New articles in the low-price segment appear from time to time under new names. Some work somehow, but others not as expected. A genuine purchase recommendation is only the DR 75 (or better) when it comes to meaningful tuning.
DR 75 cylinder with 3 transfer ports
The DR 75 tuning cylinder with 3 transfer ports is one of the most popular tuning cylinders for the Vespa PK 50 and V50. The increased displacement ensures better acceleration from low revs. The maximum RPM is around 7000 RPM.
DR 75 tuning cylinder with 6 transfer ports
The DR 75 tuning cylinder with 6 transfer ports was the first available 75cc cylinder from DR for Vespa 50 and PK 50. Due to a different channel design, it has a slightly higher engine power than the DR 75 with 3 transfer ports. It was complemented upwards by the DR 75 Formula. The DR 75 with 6 transfer ports is also manufactured in this design by Olympia.
DR 75 Formula tuning cylinder with 10 transfer ports
The DR 75 cylinder is the most powerful racing cylinder from DR in the 75cc displacement class and combines both driving pleasure and durability due to its sporty design. The Polini 75 offers even better performance than the DR75 Formula, but it is noticeably more expensive to purchase than the DR.
Polini Sport 75 tuning cylinder
The Polini 75 Sport cylinder is also designed for sporty performance. In the Race version, the Polini 75 comes with a different cylinder head with higher compression. Higher compression improves performance coming out of the corners, but also increases thermal stress.
Polini HP4 cylinder 75cc
The Polini HP4 cylinder set is the most powerful tuning cylinder in the 75cc displacement class. The cylinder is made of aluminum and is thermally highly resistant. This is necessary because the Polini HP4 is very sporty and delivers high peak power at high RPM. For a smaller investment, cylinders with more displacement are an alternative, provided you are not limited to 75cc. 102cc cylinders provide comparable or even more power for less money than the Polini HP4.
Malossi 75 tuning cylinder
The Malossi 75 cylinder is a sportily designed and high-quality manufactured cylinder. The precise dimensions at the squish band ensure the best possible performance from the cylinder set. The O-ring inserted into the cylinder head ensures that no false air can enter the combustion chamber or that fuel leaks out.
Pinasco 75 cylinder
The high-quality Pinasco 75cc cylinders are available in gray cast iron and aluminum. The high-quality Pinasco 75cc cylinder is a powerful and well-made tuning cylinder, but it does not reach the performance of the sports versions of its competitors.
Pinasco 75 cylinder for Vespa PK 50 Automatic
The Pinasco 75cc cylinder for PK50 XL-XL2 Automatic is currently one of the last tuning cylinders for the Vespa Automatic. With this cylinder, it should be considered that the original cylinder head must continue to be used because no cylinder head is included in the scope of delivery. The adjustment of the cylinder head is carried out, for example, by the specialists at MMW. Update: We now have the Pinasco 75 cylinder with matching cylinder head in stock.
Channel adjustment
In 75cc cylinder tuning, no milling work is generally necessary. However, those who still want to optimize the mixture flow can
- adapt the transfer ports of the engine housing,
- and work on the shape and size of the cylinder exhaust (square, oval, trapezoidal).
Squish band
The squish band on the cylinder head does not need to be considered for cylinder sets with small displacement. However, when tuning cylinders with a sporty design, this is a factor to consider. With a value of 1.3mm (without guarantee), a squish band has high compression and at the same time not too high thermal stress. There are engines that are driven with considerably less squish band. However, there are also original engines that additionally have very large squish bands due to high tolerances and still drive reasonably. Reasonable, however, means sluggish - after all, the article deals with optimization / tuning.
Timing
To change the characteristics of an engine, the camshaft timings should be determined. The timing calculator is very suitable for this purpose.
The more power an engine is intended to deliver, the more decisive the camshaft timings become.
Racing Crankshaft
Changing the crankshaft is not necessarily required for 75cc tuning. However, the advantage of a racing crankshaft lies in the fact that the fuel mixture can be sucked into the crankcase chamber over a longer period of time due to the extended camshaft timings, ensuring optimal fuel supply to the cylinder even at high engine speeds. For the Vespa PK 50 XL/XL2 with the large taper, we recommend the Mazzucchelli racing crankshaft for Vespa PK 50. If you have a Vespa V50, then the upper connecting rod bearing in the original Piaggio crankshaft is designed as a plain bearing. Piaggio changed this for the PK 50 and replaced the plain bearing with a needle bearing in addition to the larger taper. When tuning a Vespa, a crankshaft with a needle bearing should always be used. Only this type of crankshaft allows for high mileage with increased torque from a tuning cylinder. The appropriate racing crankshaft, i.e., a crankshaft with a needle bearing and longer intake camshaft timings, would be the Mazzucchelli racing crankshaft for Vespa V50.
If the condition of the original crankshaft is still good, i.e., none of the following points apply, the crankshaft can be overhauled/modified.
- lower connecting rod bearing makes noise / is stiff
- rotary valve shows damage such as grooves or similar
- connecting rod is worn
- connecting rod is bent
- crankshaft cheeks are twisted
- engine vibrates strongly during operation
Carburetor
Changing the carburetor of the Vespa PK50 S-XL2 is not necessarily required when tuning with a 75cc racing cylinder. However, the SHB 16.10 carburetor of the Vespa V50 should be replaced with an SHB 16.16 carburetor with the corresponding intake manifold. The SHB 16.12 of the Italian Vespa HP4 is also a restricted carburetor and should be replaced with the unrestricted 16.16. Remember to adjust the carburetor jets to the new engine setup. Instructions for cleaning and adjusting the carburetor can be found in the instructions section.
Exhaust
A racing exhaust makes limited sense with 75cc cylinders because a racing exhaust is acoustically much more noticeable than the cylinder, but it only offers little additional power for most 75cc cylinders. For the Vespa PK 50 S-XL2, we recommend a Sito Plus or an original exhaust system. A banana exhaust also works very well for the Vespa V50. For the PK 50 frame, part of the spare wheel cover must be removed for the installation of the exhaust manifold. The banana exhaust is also available as an inexpensive replica from Sito and Faco. A more noticeable racing exhaust like the Polini Banana only makes sense with larger cylinders such as the Polini 112cc or the Polini 133cc. For those who desire a louder exhaust sound, the "Polini Snail" works quite well even from 75cc.
Increasing Top Speed
The primary gear does not necessarily need to be replaced when tuning with 75cc cylinders. Therefore, opening the engine is not necessary, provided it runs smoothly otherwise. However, the higher torque of the tuning cylinders can be better utilized with a longer primary gear. On the one hand, the top speed and driving comfort increase because the lower gears can be used sensibly. Furthermore, it is then easy to keep up with traffic in the highest gear without the engine running at such high speeds. To fully utilize all gears up to the maximum engine speed, we recommend the 3.72 primary gear for the Olympia 75 / DR 75. For lightweight riders and longer overland trips with full throttle and downhill sections, the 3.00 primary gear may be the better choice, even though the maximum engine speed in the highest gear is often not reached. In an earlier article, you can find information on selecting the optimal gear ratio. The clutch linings do not necessarily need to be changed when tuning Vespa. For optimal power transmission, only a reinforced clutch spring should be used for the Vespa PK50 S, XL1, and for the V50. For the PK50 XL2, 6 reinforced clutch springs are then required, which are usually also always in stock in the shop. We wish you a lot of fun tinkering and a safe ride!