Help Needed On Dyno - Turbo Busa Only Making 105 Bhp With Boost Pipe Off. :(

hey guys, havn't posted for a while. lifes been busy with other things for a while.
bicycles, ice racing cars, maintaining boring daily drivers etc..

i have three busas here at the shop. one fully stock. my own home build 8psi turbo.
and one im building for someone else, for higher boost.

the higher boost one is the problem i need help with.
i had this thing running great back in the summer. at 240 bhp rear wheel.
we then decided to run it on C12 and up the boost a bit,
it has aftermarket rods and pistons.
so i boosted it upto 340 bhp. playing with different injectors etc..
then while doing a lot of dynoing. the clutch started slipping. BADLY

so it was taken off and had a billet basket, APE spring kit, and support bracket and new suzuki clutch disks.
i also removed the power commander V pti. and put stock injectors back on, and did some machining/welding. so theres now 4 S2000 injectors in the plenum.
these secondary injectors are to be powered by a controller by a company called SDS.
annddd.... changed to a slightly larger, and Ball bearing turbo.

so.... its finally back on the dyno now. and before i start adding boost i just tried a couple of runs with the boost pipe off. 43 psi fuel pressure. stock ecu. stock injectors.
i got crappy stuttering and SLOW....... 49 bhp !

finally found one injector wasnt working. replaced that and cleaned them all.
back to the dyno - - - - - 102 bhp !
this is repeatable.... every time. 101 - 102 bhp.

it seems rich at idle. for it all being stock fuelling.
i have 12-12.7 on the ARF gauge. the whole time. from idling at 12 to 12.7/12.5 through the run.

i really want to fix this and see 145 bhp roughly before i start boosting things.

-i recalibrated the throttle position sensor.
does anyone have testing spec for air box sensor ?
and coolant temp sensor ?
could those be it ?
-i have checked and confirmed Cam timing is still perfect.
-a have watched the fuel pressure gauge during a run. and its maintained and fine.
-i have checked and cleaned out the fuel filter.
- SDS system and extra injectors are all currently switched off.
- in dealer mode i have no codes. and the TPS sensor line is central.
- i replaced last summers C12 with fresh 91 gas.
- the cam sensor is clean and the pin in the cam has not moved or fallen off haha

it starts up perfect,idles, revs and sounds great IMO
even sounds good during a run to be honest. just 102 bhp not 150bhp :(

what do you think i should check next ?
should i try a spare ECU ?

THANK YOU in advance hayabusa wizards !!!!! :)


I would Take the wastegate off not the up pipe
you will overspeed the turbo with no load
Dont forget besides the question Rob asked you also are choking the exhaust, small inlet size and small plenum compared to a std busa
thanks guys !!

i have wossner pistons and an .080" cylinder spacer.
so i believe i have a 9:1 comp ratio.

i will reconnect the boost pipe. let the exhaust run free through the wastegate instead.

what power do you think i should have with no boost , turbo as exhaust restrictor and the plenum etc..?
thanks again


You should validate that your fuel pump is good. While the fuel pressure is good as you start to run higher rpm if the pump is failing or kinked hoses you'll see these symptoms. If possible you should also test the fuel pressure all the way through the pull. This will tell if it's a fuel delivery issue
i will double check this. thanks
i have checked for kinks etc. all good. but i should double check the fuel pressure is maintained.

though if the pressure was falling, i should see that on my AFR gauge going lean right ? and it doesnt


i will double check this. thanks
i have checked for kinks etc. all good. but i should double check the fuel pressure is maintained.

though if the pressure was falling, i should see that on my AFR gauge going lean right ? and it doesnt

Not always
thats why its best to check pressure at higher rpms and see whats happening like 9-12k
if a fuel delivery problem shows up its generally here
THANK YOU !!!!! everyone.
i put the boost pipe back on and removed the spring from the wastegate.
135 bhp at the wheel.

figured that was good enough to start boosting. ran 220 - 240 bhp pretty nice a good few runs.
but my fuel pump cant keep up now. :(
and i seem to have no battery charging happening.
so time to play with the annoying electric stuff. and possibly order a fuel pump and buy a battery,

thanks again :bowdown:


Do it right. Get a good Bosch pump, external.
Mount it on the swing arm by the shock. Keeps it low and nice and cool so no vapor lock

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