This is the latest version of the Casa Lambretta close ratio gearbox for Lambrettas. The ratios were chosen by Vittorio Tessera to offer a cheaper, sporting (non-race) 4 speed gearset. 

ALL COMPONENTS ARE NOW FORGED IN EXTREMELY HIGH-GRADE STEEL, WITH AN ALL-NEW TOOTH PROFILE, OFFERING MAXIMUM RESISTANCE!

This 4 speed gearbox is designed to fit any Lambretta Series 1 LI, S2, S3, GP / DL or Serveta scooter.

It uses a forging for the gear cluster and has been tested on the racetrack. The gearbox uses a superb set of tooth combinations. They are:
Cluster – loose gear (same ratio as) % rise
1st Gear = 11-50 (same as LI 150) 
2nd Gear = 14-41(same as LI 150) 55% rise from 1st 
3rd Gear = 16-39 (same as LI 125) 20% rise from 2nd
4th Gear = 18-36 (same as GP 200) 22% rise from 3rd

Advantages of this Casa close-ratio gearbox are :
- Close, even ratio jumps of around 20% from 2nd to 3rd and from 3rd to 4th
- The same final drive ratio in 4th gear as a GP200 gearbox.
- Top gear will give approx. 9.43 mph per 1,000rpm with 18×47 sprockets.

The last point is important because it means that you’ll need to run a big front sprocket (18T or more) with most tuned engine conversions. 

NEW IMPROVED REVISED VERSION : Vittorio Tessera has now revised these gearboxes after some issues with the first Batch. These are spot on!