Originally Posted by springfall2008
I'm pretty sure the throttle just gives the ECU a signal as to how far it's open, otherwise you couldn't do the A, B and C modes to start with?
Modes are implemented through the secondaries, as far as I'm aware of. The twist grip controls the primary throttles mechanically (through the cables) and the ECU can, in fact, read their position, through the TPS and it can then command the secondaries to close, so that the total flow through the intake is the same (give or take) as if you'd opened the primaries X% less. The other scenario is not possible, because if you only twist the grip let's say 50%, you only open the primaries 50%. No matter what you set the secondaries to, you can't undo the restirction of the primaries and increase the flow through the intake.
By the way: The dual throttle plate bodies of the GSXRs have all the components necessary for a throttle-by-wire system. For instance, one could easily modify them to be one, by just removing the primary throttle plates (but not the shaft), and flashing the ECU so that the secondaries follow the TPS across the RPM range (which is possible since, as far as I know, the STVA maps are RPM x TPS). I've often wondered why Suzuki chose to go with this setup, instead of a cheaper, more compact, throttle-by-wire system (which could trivially implement the current behavior). I can only think of safety reasons, (since a failure of the secondaries can only close the throttle and is therefore not as critical), but then I wonder how the actual ride-by-wire systems deal with such concerns...