Le Espansioni

rumiesp (13K)

Moto Rumi Expansion Chambers

As two stroke (due tempi) fans know, a proper expansion chamber type exhaust can provide a tremendous performance improvement over a standard exhaust system. All standard road going production type Rumi's were fitted with standard restrictive mufflers. However, the racing Rumi's were often fitted with a short megaphone type exhaust. This was astonishingly loud but not as effective as a real expansion chamber type exhaust. L'ingegner Guidorossi (Engineer Guidorossi) developed expansion chambers for Moto Rumi and these were first used in the Giro Motociclistico d"Italia in 1955.

How do two stroke and expansion chambers work. Check out my Due Tempi & Le Espansion Theory to see an overview. Note this page contains a 531KB animated gif that may take a long time to load if you have a slow internet connection.

A drawing by Guidorossi is shown below with the attached text from the Rumi bible, "Rumi: La Moto Dell'Artista" by Riccardo Crippa (This book is out of print and practically unobtainable). If you ever see original Rumi espansioni or replicas you will see the pipes look like regular cylindrical mufflers. This is because the actual cone shapes were hidden inside that clyinder. You can see this in Guidorossi's drawing. The cones were hidden for two reasons; Rumi considered the cylindrical muffler shape more esthetically pleasing and it hid the actual secret design of the expansion chamber. The last paragraph of the page from the book says something to this effect: After the 125 Grand Prix, the MV Agusta rider Angello Copeta asked why Zonca Gianni's Rumi had become uncatchable exiting the curves. The reason was the new expansion chamber exhaust!

I have also included two pictures below of expansion chambers that I have seen on Rumis. These both appear to closely follow Guidorossi's design.

Click on the picture to download. Each is between 55KB - 125KB.

Return to Ruminations