Test Vespa Box exhaust
Boris Goldberg, in collaboration with MMW Racing
a very complex exhaust test for the
Vespa PX200 models on behalf of the very informative
English online magazine ScooterLab.uk (SLUK for short) for short. The focus of the test was on the now very popular box exhaust systems. This means exhaust systems that are more or less similar to the original exhaust in appearance and sound, but offer much better performance, such as the
BGM BigBox Touring or Polini Box. To make the results available to all readers, here is an excerpt of the most interesting tests. In general, tests were carried out on two different engines:
- Original PX200 12hp engine
- PX200 engine with Malossi 210 sports cylinder, long-stroke racing crankshaft (60mm stroke with extended intake timing angle), SI24 carburetor
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EXHAUST COMPARISON PX200 ORIGINAL ENGINE
The original PX200 engine is designed as a throttle motor. As a result, it offers high torque with a flat power curve. Due to the short control angles and small scavenging surfaces, the engine cannot be operated sensibly with a classic racing exhaust. The loss of torque in the lower range is so great that it can lead to problems with the gear connection from third to fourth gear. The engine falls precisely into the range in which the racing exhaust has significantly less power than the standard exhaust at shift speed. Under unfavorable conditions, the engine then literally starves in fourth gear and does not get any faster than in third gear. In addition to the visual and acoustic inconspicuousness, this is one reason why the box exhaust systems have become so popular. These offer a much more linear power curve without a drop in performance, while delivering almost the same power as a 'real' racing exhaust. This means that the engine with a box exhaust is generally much more harmonious and relaxed to ride. The Polini Box and Big Box Touring are a perfect example of how a good exhaust system can give a standard engine a boost. Polini has developed its exhaust system very close to the Big Box Touring, which was previously available on the market. On the original engine, the BigBox Touring is clearly ahead in terms of torque and power:
POLINI BOX ON THE PX200 ORIGINAL ENGINE
The performance curve of the original Piaggio PX200 exhaust always serves as a reference. In addition, an exotic, non-saleable model was included in the diagram (an exhaust from the special model PX125 T5, which was fitted with a PX200 exhaust manifold). The Polini box runs very smoothly on the standard engine. It extends the usable speed range and increases the available torque and power quite considerably. Compare the lower yellow curve of the original exhaust with the upper red curve. The engine speed is indicated via the left/right axis and starts at 2800 rpm. The engine power is read off the vertical axis, the higher the curve, the higher the engine power at the given speed. The original exhaust achieves 9.5 hp here, which is the normal rear wheel output of a 12 hp Vespa. The 12 hp is measured at the crankshaft at the factory, without the losses due to the gearbox, tires, etc. The Polini box achieves a maximum of
11.5 hp, already 2 hp more than the standard exhaust. The absolute torque is identical to the standard exhaust.
Performance data and improvement compared to the original exhaust: 11.5PS/16.2Nm (+2.0PS/+0.0Nm)
BGM BIGBOX TOURING ON THE PX200 ORIGINAL ENGINE
The BGM BigBox Touring runs much more powerfully on the standard engine than the Polini. Up to around 5700 rpm, i.e. exactly in the speed range for which the original gearbox was tuned, the BigBox Touring is clearly superior to the already good Polini box. The slightly earlier end of the rev range at 7000 rpm (Polini 7400 rpm) is not relevant, as the standard engine only revs up to 6000 rpm in fourth gear anyway (due to the normal driving resistance). On an original engine, the BigBox Touring is therefore still unbeatable when it comes to early, high torque with a very good bandwidth. Without further modifications, it gives the original engine a plus of 2 hp. Compared to the Polini, it also increases the absolute torque by more than 1 Nm. This is already noticeable when riding, as this higher torque extends over the wide speed range of 3000-5500 rpm, which is very important for everyday use.
Performance data and improvement compared to the original exhaust: 11.5PS/17.4Nm (+2.0PS/+1.2Nm)
EXHAUST COMPARISON ON THE PERFORMANCE-ENHANCING ENGINE WITH MALOSSI 210 SPORTS CYLINDER
Despite the modified cylinder and crankshaft, the converted engine in this test is still extremely touring-friendly and rock-solid with classic Vespa characteristics, albeit very sporty ones. As a result, the engine develops at least as much power from low revs as a standard engine, with significantly better performance in the mid and upper rev range.
POLINI BOX ON PX200 ENGINE WITH MALOSSI 210CCM CYLINDER The Polini Box works very well on the Malossi sports cylinder and offers a considerable increase compared to the original exhaust (+5.4 hp). Up to 4200 rpm it is slightly below the level of the original exhaust, but then from 6000 rpm it picks up speed again and offers good top performance.
Performance data and improvement compared to the original exhaust: 21.2PS/23.7Nm (+5.4PS/+3.4Nm)
BGM BIGBOX TOURING ON PX200 ENGINE WITH MALOSSI 210CCM CYLINDER The BGM BigBox Touring works perfectly on the Malossi sports cylinder and offers a very high torque practically from idle speed. At 5000 rpm it is a whole horsepower stronger than the Polini box and reaches its peak performance at 6000 rpm. Here, too, the name says it all and every touring rider is on the safe side with the BigBox Touring in terms of perfect rideability and thrust from the engine speed range. Compared to the standard exhaust, +3.5 Nm are extracted from the engine, all at a significantly lower rev level. Those in a hurry can benefit from the wide rev range of the BBT, which still allows the engine to easily rev up to 7500 rpm with plenty of power at the rear wheel. With a standard gearbox, this is already over 125 km/h, while such an engine can easily pull a longer gear ratio. Fast freeway stages are therefore not only no problem despite the early use of torque, they are also great fun!
Performance data and improvement compared to the original exhaust: 19.9PS/23.8Nm (+4.1PS/+3.5Nm)
BGM BIGBOX SPORT ON PX200 ENGINE WITH MALOSSI 210CCM CYLINDER Fans of classic two-stroke characteristics will love the BGM BigBox Sport. If you are looking for a resonance kick*, a wide rev range and high peak power, this is the right choice for you. It is still somewhat underpowered on the Malossi sports cylinder, but this is ideal for anyone who wants to expand their engine concept. The Malossi sports cylinder is perfect for this, as it offers the same overcurrent layout as its much more powerful MHR brother. The latter works best on a diaphragm-controlled intake (or a heavily revised rotary valve intake) together with a large carburetor. Therefore, MHR was not used as a basis in this test. However, by increasing the head angle and the exhaust window, the Malossi sports cylinder quickly reaches very high power levels. Engine outputs of well over 25 hp are then easily possible with the BBS, as the BigBox Sport is also known for short. But even on an engine with a fairly conventional design, such as the one used in this test, the BBS is the winner in terms of top performance. The nice thing about it is that despite having the highest peak power in the test field, it runs almost as powerfully as a standard exhaust up to 5000 rpm. This is rather unusual for exhaust systems with high peak power. But from 5000 rpm there is no stopping and the exhaust starts to charge fully. The high peak power is then maintained over a wide speed range. Perfect for chugging inconspicuously through the city and occasionally unleashing the power hammer. As already mentioned, the BigBox Sport works much better on more powerful engines and does not stop at an output of over 30PS/30NM (see also the
performance diagrams in the online shop).
To summarize, the BBS is the proverbial wolf in sheep's clothing. (*you can feel the turbocharged use of the exhaust)
Performance data and improvement compared to the original exhaust: 22.0PS/23.7Nm (+6.2PS/+3.4Nm)
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