Alex builds a Quattrini 252cc Vespa engine 4 - expansion stage 2 with exhaust test

In the fourth part of our short blog series, we make the following modifications to our test engine: The cylinder is fitted at the base with two 1mm spacers by a further 0.5mm compared to stage 2. This changes the control angle of the transfer ports from 124° to 126°. The outlet is adjusted to a control angle of 190° by milling. For this purpose, the outlet in the cylinder was raised by 1.8 mm. The exhaust width remains unchanged at 57%.

The first tests are carried out with the Elron

Slightly more nervous exhaust systems would show a clear deflection in the direction of performance with the changes made, but the Elron is almost unimpressed by the cylinder's specifications and retains control of the engine's characteristics. A slight increase in the maximum values after the decimal point merely indicates that the Elron has taken note of the fact that the cylinder is sending a clearer signal through the exhaust. However, the maximum torque still remains at the same level as in the first stage. The available speed range is reduced by 500 rpm to 3540 rpm.

Polini Box

As a box exhaust, the Polini exhaust system reacts rather as expected. Similar to the Elron, the can from Italy also shows only minor reactions. The lower effective compression causes the curve to dip slightly on the rise between 4000 rpm and 6200 rpm. The system implements the slightly increased time cross-section at the exhaust window with a gain of just over one hp at the peak. The maximum torque remains the same at 35.2 Nm and only shifts a few hundred revolutions towards higher speeds. With a bandwidth of 3800 rpm, the Polini system lags slightly behind stage 2, but this test shows that the box does not necessarily prefer the very small control angles. In direct comparison to stage 1, the bandwidth and maximum values have increased significantly.

JL left hand / JL-Performance

Our test subject had a short break in the previous stage due to appointments away from home, but is now playing again in the third stage. Therefore, here is the comparison between stages 1 and 2, which also shows very clearly how clearly an exhaust can behave when it is operated from other control angles. The JL, which is considered to be good-natured, turns out to be a very responsive partner in the search for power. At its peak, the JL provides almost five and a half more horses and climbs above the 36 hp line on the graph. At 32.6 Nm, the torque remains at the same level as in the first attempt. However, the torque extends over a significantly wider band - beyond 7000 rpm. The power peak of 36.4 hp is reached at 8400 rpm. The JL only falls below the 25 hp line considered in the bandwidth beyond 9600 rpm and can therefore not be described as lazy. In general, the graph clearly shifts towards higher engine speeds. With a bandwidth of only 3400 rpm, the JL even lags behind the Elron and brings up the rear in terms of bandwidth in this construction stage.

Scooter and Service Newline

The angular bruiser from the north feels right at home in this configuration level and takes two best values straight away. The Newline does not make any notable changes in terms of acceleration, but it does improve considerably in the rev range thanks to the larger advance angle. With 37.3 Nm, it takes the top position for torque in the third stage. Although the available speed range is narrower compared to the previous tests, the Newline still manages a range of 4000 rpm. With these values, we are already thinking about a longer primary with 24-60...

Nessie

Like the Elron, the sea monster from Posch Performance is still not quite sure what to do with the changed steering angles. The maximum torque remains the same and the peak power increases by one horsepower. While the Nessie was still far ahead in terms of bandwidth at 4300 rpm in stage 1, the available speed range dips a little in stage three and is in the upper mid-range at 3700 rpm.

Racing Resi

The Racing Resi tastes the changes better. More inclined towards the higher steering angles, the Resi develops one hp more at the top end and adds torque, which hardly affects the bandwidth on the 25 hp line. In absolute terms, the Resi holds the position of highest peak power at this level with 38.9 hp. In general, we are slowly approaching the 40 hp mark with the expansion stages.

Lakers

At 126° to 190°, the Lakers is not yet in its comfort zone. Although it also clearly converts the changed steering angle into power. With 38.4 hp at its peak, it is only just behind the Resi. With a rev range of 3700 rpm, which already extends to 10,100 rpm, the Lakers shows where the journey can take you with the right peripherals. Here is an overview of the results. Best values are highlighted in green.