I eventually traced this to the Throttle Position Sensor which should (on a Hayabusa bike) output between 1.1v and 4.3v to the ECU (closed > open throttle), but I was seeing 5v on the output wire... sometimes... other times it would behave, then other times it was all over the place.
Anyway, found 1 damaged wire on the TPS and another wiring loom pin that was lose in the connector so not making a good connection at all.
I'd removed the TPS from the car at this point, but was unable to calibrate it to the ECU when I bolted it back in place - I do not have the hardware to connect the MBE ECU to a laptop to query it, so I didn't know what voltage the ECU was expecting to see at closed & wide-open throttle.
Even a small movement of the TPS caused a big difference in how the engine would run. I couldn't get it right. Car was awful on transition from off to on the throttle at very light loads - juddering, kangarooing, really annoying to drive slow.
(Turns out I'd set TPS to 1.12v, which was enough to cause issues. I now know that the ECU is expecting to seeing exactly 1.18v from the TPS when throttle is closed and the engine at idle).
Anyway, a trip to RLM Racing was scheduled and I booked the day off work. These guys are experts at building, modifying and tuning the hayabusa engine. They are a very long way from me, but I figured it's better to get these things done properly. Their brief was to get the engine running right and review and tweak the ECU map with a rolling road session.
Set off mega early and arrived 3 hours later at 08:40 in a small village (town?) just north of Corby. All good - got a coffee on arrival and explained the issues and car set up, and then set about taking the body work off and allowing the guys to strap the busa down to the rollers.
Now - I've never had this car rolling roaded and never seen a power figure for it. All I know if the previous owner told me it had made about 210 at the wheels in 2015/2016.
The car was warmed up and then given a power run up to 9,750 rpm to see what it was making, and to set a reference point for the work that was to follow. Figures were pretty good actually... 229 bhp and 144 Ft.lbs.
Rich at RLM then set about calibrating the TPS so that it was matching the figures that the ECU was expecting to see (1.18v at idle), and then the next two hours doing multiple runs on the rollers to tune all areas of the ECU map - loads of time spent fine-tuning the low-end and mid-range stuff, and transition when coming on the throttle.
Final headline figures were:
249 bhp@9855 rpm and 155 ft.lbs@6570 rpm. These are calculated figures at the flywheel.
Actual figures measured at the wheels were 212 bhp and 132 ft.lbs.
I'm happy with that.
Making the power I'd expected and the torque curve seems pretty good to me... certainly a reasonable amount of torque for a bike engine, and a good spread of it. Graph is below... the two lower lines (green and purple) are the BEFORE TUNING plots. So you can see that it didn't drastically alter the power/torque curves, just raised them a bit. Picked up 20 bhp and 11 lb.ft.
RLM generally leaned the map off quite a bit from 7,000 rpm onwards - was running too rich apparently.
The car behaved really well on the rollers. The guys at RLM said they wished that all rolling road sessions went that smoothly. Nothing broke or needed fixing, no fluid leaks, no over-heating. The guys seemed pretty impressed with the engine, considering the budget nature of the turbo conversion.
The only feedback that I should consider was...
- injectors are too big really (they are Siemens 690cc). Rich said he'd have better control at light loads with smaller injectors, maybe 400cc. Nothing major though - not worth changing.
- plenum chamber a bit small. Said could get smoother transition when coming on throttle with larger plenum.
- boost is creeping up with rpm after about 8,500 rpm. This could be because it is a sh1tty chinese ebay turbo
and the wastegate cannot flow enough, or more likely, that the actuator is just too strong for the small amount of boost I'm running. (Actuator is set with no pre-load at all, and I'm guessing it is spec'd for 15 psi+ really, whereas I want to run 6/7 psi). The car is holding 6.5 psi up to 8,000 rpm but this then creeps up to 9 psi at 10,500 rpm. So, all in all, I'm very pleased. Car is 100% more drivable at lower revs, and so much smoother when coming on/off the throttle. AFR steady, and I expect fuel economy to be better. Great result. Roll on the Euro road trip next weekend!
