Alex builds a Quattrini 252cc Vespa engine 5

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Part 5 for stage 4

Fortunately, as with so many things in life, everyone has their preferences...
More RPM and more peak power or more torque at low RPM.

That's why in today's part I'm looking for more... But not top performance, but for speed range and torque. The "tractor engine" is sought.

In part 4 with stage 3, I looked in the direction of the higher control angle by raising the cylinder and making a small adjustment to the exhaust. If I were now to increase the exhaust further in order to perhaps achieve higher peak performance and speed, the way would be backwards; to try the cylinder with more blowdown at lower control angles installed.

So today I lower the cylinder. Overall, this results in lower control angles, but the pre-release increases slightly. The smaller transfer angle should allow the cylinder to produce a little more torque at low rpm.

The spacer on the cylinder head was changed from 1mm to 3mm compared to the third construction stage. At the cylinder base, the 2mm spacer leaves the field and the cylinder is only supported by a normal 0.3mm thick gasket. The squeezing edge remains at 1.3mm, as with the other construction stages.

In the following graphs are the current curves of construction stage 4 RED to see. The curves from the previous stage three appear in BLUE.

Elron is the first to show what he thinks of the change.

As can be expected, the absolute top performance drops slightly, but the maximum performance and torque shift in the direction of lower speeds. The torque increases slightly and feeds the range between 5100 and 7000 rpm.

The Polini box, which is more intended for engines with less transfer time, is placed next on the exhaust port.

At first glance, the curves may seem sobering. On closer inspection, the Polini Box turns out to be a real torque animal. At the end of this series of tests, it will rank second in terms of torque with 37.4Nm. The graph already passes the 4700 hp mark at 20 rpm. The maximum power shifts by an impressive 1000 rpm in the direction of a lower speed, culminating at 6400 rpm. The maximum torque pulls at the rear wheel at 6000 rpm. An engine constructed in this way is just begging for a long gearbox.

This allows the M244 to move over the asphalt with extreme shift laziness. Jack off the stand, shift into gear 4 and just pull the cable. Don't worry, it will be quick...


The aged all-rounder in the field.

The JL left arm puts its torque in the range between 5000 and 7000 rpm and thus offers more drivability. Although the peak power falls by one hp, the JL can still offer very good drivability in the field of resonance exhaust systems.

New Line

The handwork from the north is also responding to the adjustments as expected. Already at 5000rpm, 20 horses are ready to move significantly. Full torque is available at 6100 rpm. Although it pushes the absolute top performance down a bit and the Newline gives up 2 horses in favor of the early torque, it is happy to take the larger pre-release in order to go over 10.000 rpm and maintain it there with over 20 hp.
The Newline behaves here almost like a box exhaust system, seasoned with a significant torque kick.

Posch Nessi

The sea monster ducks its head slightly due to the reduced steering angles. But that's not bad at all. As with the Newline, the rev range shifts slightly towards early revs and develops more torque in the process. At 5200 rpm the curve already exceeds the 20 hp mark. The slightly increased pre-let helps the Nessi to a wider speed range.

Posch Racing Resi

The lush Resi handles the steering angle that is unsuitable for you amazingly well. Although it also loses peak performance, it gives an idea of ​​the bandwidth that can be possible with the appropriate control angles and more forward airflow. With a speed range of almost 4100 rpm, it is in the top league here.


The Lakers, made for a lot more alert, don't like the slack head angles that much. The exhaust craves for larger time cross sections. The speed range shifts to lower speeds as expected, but the low time cross sections are not the right playing field for the Lakers. But his chance will come with the following expansion stages...


Here again all maximum values ​​in the overview