Split personalities
How the new 2024 Fireblade SP’s dual throttle-by-wire system boosts both power delivery and engine braking
Honda are pulling no punches with the new CBR1000RR-R Fireblade SP, now promising some of the most advanced technology on the market, in a bid to take top spot in the latest superbike arms race.
This includes a new two-motor throttle-by-wire system that promises improvements in engine behaviour at relatively little expense - a system that is likely to spread across the range after its debut on the latest SP.
The idea is a logical extension of the ride-by-wire throttles that have become ubiquitous on modern bikes. Those already eliminate the direct connection between right wrist and butterflies, allowing reduced emissions, better economy, and improved response.
Honda’s two-motor throttle-bywire is essentially a set of four throttles that are operated in two pairs, each with their own actuator, rather than working in unison.
One actuator operates the throttles for cylinders one and two, the other controls cylinders three and four. Working independently under the control of the bike’s ECU, they allow Honda to implement a whole array of strategies that wouldn’t be possible with a conventional setup and have been the subject of at least two new patent applications from the company, potentially preventing rivals from copying the idea.
Big bang theory
The throttles for cylinders one and two operate relatively normally, opening and closing in response to the twistgrip, but the butterflies for cylinders three and four work rather differently.
On smaller throttle openings, for instance when you’re trying to apply the right amount of gas mid-corner, the second set of throttles initially stay closed to make the first two cylinders responsible for most of the engine’s performance output.
That means throttles one and two open further than they would on a conventional engine, giving a more granular level of control and avoiding the inconsistent combustion and torque output that
can accompany very small throttle openings on some bikes.
What’s more, with only two cylinders providing the lion’s share of the torque at this stage, you get something similar to a ‘big bang’ power delivery despite the engine having a conventional, evenly spaced firing interval.
That improves traction and rider feedback, allowing more time for the rear tyre to regain traction in the gap between power pulses.
“The torque simulates that of a two-cylinder engine,” Honda’s patent explains.
Open the throttle wider, as on the exit of a corner or on a straight, and all four throttles respond, giving the outright power advantage of a conventional ‘screamer’ fourcylinder with even-spaced combustion characteristics.
But the benefits aren’t just during acceleration because the system also operates when you close the throttle, adding a new level of engine braking control. When the bike decides you need extra engine braking, it can independently fully open the throttles of cylinders three and four while keeping the fuel supply cut off. That allows more air into those cylinders, increasing pumping losses as it’s sucked in, compressed, and expelled, for an overall increase in engine braking.
Since all these gains come from the relatively simple addition of one extra throttle actuator, a secondary ECU and some additional programming, they shouldn’t add much to the cost of a bike. As such we could see other Honda fours, and even twins, could adopt the same idea in the future.
A sub-ECU is responsible
for operating the second pair of throttles, working alongside the main engine ECU that controls the rest of the engine systems, including the ignition and injection as well as the first pair of throttles.
The system draws information from wheel speed sensors, rpm sensors, the IMU, gear position and even the air temperature before deciding how to respond to commands from the twist grip.
‘Cylinders three and four work independently’