2011 09 14 Dyno Run

The latest dyno run was done on the new Scooterlabs dyno, which is a dyno setup to read true rear wheel HP (not estimated at the crank). On previous dyno runs I had issues with mapping the rpm correctly due to various reasons (e.g. dyno setup for standard Vespa gearing and then I hop on with my long gearing). Also all dyno runs were done in third gear. So the lab session was to do a few things:

  1. Wind her out in 4th gear and see what the top speed is based on mph alone (not post-calculated from rpm)
  2. Do the dyno with the tyres pumped up to race pressure
  3. See how the tyres handle 100mph


The results:

  1. Blue is 3rd gear, Red is 4th gear. Even with a Malossi 24/63 upgear, the current peak power (32hp) is at ~86mph (7500rpm) fading out (21hp) at around ~95mph (8500rpm). With no juice at all by 100mph (just under 9000rpm).
  2. The increased tyre pressure and reduced rolling resistance gave a peak power of 32hp at the rear wheel (which on dyno's that estimate crank hp would read 42hp)
  3. The rear wheel (and the rest of the motor) handled the speeds fine

Note: I estimate that 25hp is required to do 100mph


  • Get a DRT 33 Tooth Long 4th Gear
  • A better and shorter carb manifold which is less restricted will push out the top end rpm
  • The super charger planned may also push out the top end
  • Maybe a 35mm or 36mm carb would improve power, the 38mm may(?) be too much. Though with a super charger probably not
  • Maybe alter the expansion chamber to drop the top end power more slowly (diffuser taper angle) or target higher rpm (length)
Paul McIntosh,
Mar 24, 2015, 11:42 PM
Paul McIntosh,
Mar 24, 2015, 11:42 PM