09-09-2020, 01:55 PM
Outcome so far. We went a few miles in Duncan's special, around roundabouts, then on open road, and return. Some of the route is flat and some is a slight gradient. Then we repeated the route in my Ruby.
Mine is 5.25 axle ratio. 17" wheels, LC head. Zenith sidedraught. max speed 49mph
Duncan's is 5.25 axle, 19" wheels, HC head, Solex downraught. max speed about 45mph
Both speeds were measured with the same sat nav device.
To keep mine at top speed needed full throttle.
Approaching top speed in the special it seemed to make little different whether the pedal was to the floor or a bit less.
In both cars I don't think the engine was running out of revs, but the engine wasn't developing enough power to overcome the increasing air resistance. Air resistance is proportional to the square of the speed. The 19" wheels will make the special slightly higher geared, so slightly less revs at a given speed. Power is torque multiplied by revs so the power might be less at less revs, or if the higher revs are getting beyond the engine's peak, then the less revs can mean more power.
To some extent guessing, but i think the special suffers from a non-standard exhaust system, and also the body might be quite high air resistance. It might be interesting to try the ruby again with all the windows closed - it can make a difference.
Mine is 5.25 axle ratio. 17" wheels, LC head. Zenith sidedraught. max speed 49mph
Duncan's is 5.25 axle, 19" wheels, HC head, Solex downraught. max speed about 45mph
Both speeds were measured with the same sat nav device.
To keep mine at top speed needed full throttle.
Approaching top speed in the special it seemed to make little different whether the pedal was to the floor or a bit less.
In both cars I don't think the engine was running out of revs, but the engine wasn't developing enough power to overcome the increasing air resistance. Air resistance is proportional to the square of the speed. The 19" wheels will make the special slightly higher geared, so slightly less revs at a given speed. Power is torque multiplied by revs so the power might be less at less revs, or if the higher revs are getting beyond the engine's peak, then the less revs can mean more power.
To some extent guessing, but i think the special suffers from a non-standard exhaust system, and also the body might be quite high air resistance. It might be interesting to try the ruby again with all the windows closed - it can make a difference.