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The new 177 – cylinder for Vespa

We have already presented the new cylinder in this post. Today we would like to offer you an insight into developing this cylinder. The cylinder will finally be available from beginning of April 2016!

Developing the Vespa cylinder BGM177

Developing a two-stroke cylinder is very exciting.
Numerous parameters, which need to be considered, thousands of times on the dynamometer, a repetition of measuring, calculating, testing, thousands of kilometres on the road…

What for? To have a final cylinder, which offers high torque and is willing to deliver maximum performance, at the same time resistant with a low consumption.
And we want it all. A cylinder for tourers, which can be combined with standard components, and for ambitious tuners, who want the highest performance possible. It is about offering the widest range possible.

We would like to give you an insight in the tests, which have been conducted for the BGM177.

THIS IS 177

DESIGN OF TRANSFERS

We tested various options for the outer design of the transfer ports.
We designed various transfer geometries, trigger delay angles and combustion chambers, which were put to practical tests on the road as well as on the dynamometer.

BGM177 cylinder test

TEST ENGINES SPRINT150

We have been using an original Piaggio Sprint engine as starting point for our tests and for some we also have been using a LML engine casing with original inlet membrane control.
The Sprint engine casing represents the very small, original rotary valve inlet of largeframe engines. The rotary valve inlet of a PX125 is only minimally larger than the inlet of Sprint engines. Trigger delay angles of the crankshaft are almost the same. In terms of possible performance, this was the “least attractive” package. However, we wanted to know the performance with basic parts or rather which performance we could expect of the rest.

We have already presented the comparison of a Spring engine with a 24mm SI carburetor of a PX200 and a 12HP 200 engine.

In order to easily understand the following graph, just imagine a normal PX200. With a standard 200cc you will feel something like acceleration up to a speed of about 90km/h. This speed represents about 5500min?¹ of the engine. Once you have reached this torque with a 200cc engine, it will take some time to get to 100km/h (6000min?¹). Now, take a look at the graphs and compare the equivalents of this torque on the blue graph and the red graph. You will see, that the BGM177 even adds more torque. In other words, while a 200 is slowly running out of steam, the BGM177 will continue to accelerate.

BGM177 vs. PX200

BGM177_ROTARY_vs_PX200_std

TEST ENGINE LML150 MEMRANE

The 125cc engine of a Vespa Sprint with small rotary valve restricts the development of performance at a certain level of performance and torque. We have therefore used a LML engine casing for varying tests and comparisons. The standard LML engine casings comes with a reed valve intake and large transfer ports in the casing and is the best basis. This can diminish the influence of e.g. an intake, which is too small, or differently designed transfer ports on the test results within one series of tests.

BGM177_9 023

It’s also fairly easy to switch between a SI carburetor and a large, grown-up intake.

We have started these tests with a pre-series cylinder with small transfers in the cylinder base
and a piston, which has been specially produced for this test.

BGM177_9 015

Why? We wanted to find out how the piston needs to be designed in order to give enough room to the transfer ports to guarantee a good situation. The piston had been constructed in a way, that the hole around the gudgeon pin close to the transfer ports could be adapted by milling.
After every little step, we put it to the test on our dynamometer to find out, which shape or which combination works best.

Kolben BGM177 V2

TEST TRANSFER PORT CROSS-SECTION CYLINDER BASE

The following series of tests has been conducted on a LML membrane engine with a 24 SI carburetor, a BigBox Touring and various versions of pistons and transfer ports.
Then, the cylinder head has still had a relatively high compression. We have reduced compression of the standard cylinder head a little to gain a wider range of performance.

The original test piston was shaped like the original PX piston. So, for the red graph, the piston skirt was closed (like for a Piaggio, Polini, Grand Sport, …).
The blue graph shows the result of the piston with a few millimetres less around the gudgeon pin. You can see such a piston on the picture above.
The green graph shows the performance with a semi-closed transfer port at the cylinder base and an adapted piston. The free space of the transfer ports in the cylinder base represents about 80% of the possible space of the cylinder.

Vergleich BGM177 Kolben und Kanal

  • RED GRAPH: closed piston skirt
  • BLUE GRAPH: semi-closed piston skirt
  • GREEN GRAPH: opened piston skirt

Result: the BGM177 can be combined with the gearbox of a 200cc engine without causing any problems and even performs better than the large 200cc engine.
From about 1982 onwards, engines of PX125 and PX150 have been fitted with a gearbox almost identical to the one of a PX200. In these cases it’s possible to directly extend the primary drive to transfer the plus of performance to speed.
We recommend using a primary drive wheel with 64 teeth. Depending on the area of use, you can adapt the total gear ratio with a clutch sprocket. The advantage of a primary drive wheel with 64 teeth is, that you may use the BGM clutch sprockets with 22, 23 or 24 teeth.
So you can set your engine for anything between “sporty and short for cities (22/64)” and “highway – provide a maximum (24/64)”.

Our next post will be on various carburetors and intakes on our LML test engine.

BGM177 – the new cylinder by BGM PRO

Cylinder -BGM PRO 177 ccm- Vespa PX125, PX150, Sprint150, GTR125, TS125, Cosa125, Cosa150

We would like to present the new BGM177 cylinder, which will be available in April 2016. THIS IS 177

First video of BGM177 – 177cc cylinder for Vespa

At Scooterists Meltdown we have shown the cylinder for the first time. The new online scooter magazine SLUK interviewed Philipp and published an exclusive video about our new cylinder:

Fits all Vespa 125 / 150 largeframe engines with 3 transfer ports.
For instance:

  • Vespa PX125
  • Vespa PX150
  • Sprint 150Veloce
  • Vespa GTR125
  • Vespa TS125 and
  • Cosa 125/150.

BGM177_1

Powerful and reliable cylinder made of alloy

We have designed a powerful and reliable companion for you.
We have put many ideas into practice to design a cylinder with the highest possible wide range of performance.

BGM1770

BGM177 was made of alloy, just like all modern cylinders.
Very good heat dissipation is one advantage, which is positive for lifespan, consumption and performance.
The cylinder hole is coated with nickel, silicon and carbide and extremely wear resistant. The forged piston is made of alloy and has two piston rings.

BGM177_8 002

Very light piston

The design of the piston paired with a high degree of silicon in the material used, generated a lightweight of 193 grams with high thermal and mechanical stability, which is positive for torque and smooth running.
The piston rings are 1mm thick and are being produced by a renowned Italian manufacturer, which also supplies leading piston manufacturers like Vertex and Meteor. The thin rings minimise friction, which increases performance and make it possible to easily enlarge the outlet duct window.
The gudgeon pin is biconic, which means that its inner ends are thinner than the middle part, further reducing the weight of moved massed.

BGM177_8 011

Alloy cylinder with ceramic coating and large transfer ports

Large ducts and large transfer ports in the cylinder are the best basis for a wide range of performance and an early torque.

The BGM177 can be combined with simple serial components, like the original SI20 carburetor and an original exhaust. This already increases performance significantly. A modern designed cylinder leads to very low consumption at high torque in the low revs range.

Cylinder with vast potential for tuning

Do you want more performance? The BGM177 offers plenty of potential and possibilities to further increase performance with a minimum of work. The cylinder reacts very well to larger carburetors and support by an exhaust like the BGM BigBox Touring.

Transfer ports in the cylinder base can easily be enlarged. The two large transfer ports on the left and on the right are only slightly covered, so that you can easily open them up with a small hand drill. So you can either fit the cylinder to an already adapted engine casing or copy the duct profile to an engine casing.

CNC-milled cylinder head

The CNC-milled cylinder head has many cooling areas and the hole in the centre of the cylinder head prevents air of being stored in the combustion chamber.
It’s also possible to place a temperature sensor in the hole of the cylinder head. This position close to the combustion chamber grants a reliable measurement of temperature.
Placing a temperature sensor below the ignition plug using an adaptor ring or above the thread outside the cooling fin are commonly used methods, but they don’t generate reliable results. In these cases you can only see the temperature of the cooling air close to the ignition plug or the temperature of the cylinder head at the outside of the cooling fin. We think that these positions are simply unsuitable to gain reliable results. BGM therefore prefers a position as close as possible to the combustion chamber.

BGM177_8 016

Combustion chamber for wide performance range

The combustion chamber was designed to grant a wide performance range. A strong expansion exhaust chamber may be used after adapting the squish gap, thanks to the design of the cylinder head insert. With a 57mm engine displacement and a touring or box exhaust you can use the provided gaskets to adjust the squish gap to 1mm.
You are using the cylinder with an expansion chamber exhaust and 60mm engine displacement? We would recommend starting with a squish gap of 1.2mm.

Timings 57mm

With an engine with a stroke of 57mm and a squish gap of 1mm, you will reach the following values:

  • Compression 10.3:1
  • Transfer timing 118°
  • Exhaust timing 171°

Thanks to the dimension of the cylinder you will only need a 4mm gap to centre the cylinder head in the hole. The gap will prevent the cylinder head to stick out into the combustion chamber, even if you adapt the engine displacement. With an engine displacement of 60mm and depending on the engine concept you can lift the cylinder even further to achieve significantly larger transfer port angles.

Timings 60mm

With an engine with a stroke of 60mm and a squish gap of 1mm, you will reach the following values:

  • Compression 10.8:1
  • Transfer timing 123°
  • Exhaust timing 173°

The outlet width is 42mm (66%) and therefore offers positive conditions for an engine with high torque at small trigger delay angles.

BGM177 vs PX 200 12HP

Plug & play with a lot of power

This is a comparison between a BGM177 and a standard Rally200 with 12HP Piaggio cylinder (comparable to a Vespa PX200 GS).

The BGM177 cylinder has not been adapted for this experiment and is used with a Sprint Veloce engine.
Intake, crankshaft and engine ports have not been adapted.
We only attached a SI24 carburetor of the 200cc models without adapting the carburetor box or engine casing and combined it with a BGM BigBox Touring.

Jets are very similar to those of a standard 200cc version:
Main air correction jet: 160
Atomiser: BE3
Main jet: 125
Idle jet: 55/160
Air filter: standard (no additional holes)

Ignition advance was adjusted to 19° before the upper dead centre .

You can clearly see the wide range of performance (straight line) and the high torque (dotted line) at idling even with a non-adjusted engine.

BGM177_ROTARY_vs_PX200_std [table id=3 /]

The next post will be on increasing performance with this cylinder and a LML reed valve engine will serve as basis.