Hi everyone!
The ORIGINAL OEM injector is the BOSCH 0-280-158-325. It features 4 holes for better fuel atomisation.
I've been unable to obtain the data sheet. If anyone can obtain reliable flow data I can do the math... For the stock 44hp engine, let's suppose a 290cc/min injector flow should be enough. For a 50hp target power (after "customization") engine,l injector should flow 328cc/min (31 lb / hr).
But injector flow depends on fuel pressure. For example: let's supose KTM OEM single injector flow to feed a naturally aspirated stock 44hp engine, considering 80% duty cycle you will need njector flow of 290cc/min @ 3.0 BAR (27.5 lb/hr @ 43.5 PSI).
At 3.2 BAR (46.41PSI) the same injector will flow 300 cc/min (28 lb/hr). 3.5% flow increase.
At 3.5 BAR (56.76 PSI) the same injector will flow 313 cc/min (30 lb/hr). 8% flow increase.
At 4.0 BAR (58 PSI) the same injector will flow 335 cc/min (32 lb/hr). 15.5% flow increase.
For a 50hp target power (after "customization") engine, injector should flow 328cc/min (31 lb/hr).
With better fuel atomisation and better idling.
All of you considering bigger flow injector, piggyback boxes, autotune, map swapping or ecu repro just to avoid eventual lean conditions after decat pipe, exhaust tube wrap, airbox lid, slip on "akrapovic" etc. may consider instead, replacing the original 3.0BAR fuel pressure regulator by another one rated 3.2 or 3.5 or 4.0 BAR (depending on how aggressive is your bike's "customization").
This will let the stock ECU do the closed loop adjustment via stock lambda O2 sensor readings. Open loop (idle, accel transient and wide open throttle) only needs to be slightly on the rich side of lambda to make power and grant engine integrity.
It's a cheaper option for a street bike and "only" requires to disassemble the fuel tank, extract the fuel pump assembly, and do the fuel pressure regulator swap... Can this reduce the lifespan of the fuel pump? Maybe. How many aftermarket hi flow fuel pumps can be purchased with the cost of a piggyback ECU plus Dyno runs, more than six, more than ten???
Having the right amount of fuel granted will be only half the work done. The ponies always hide behind ignition advance map. Avoiding lean moisture conditions will allow to use slightly aggressive ignition advance Map. A cheaper approach option would be improve faster flame propagation inside the chamber using an Iridium sparkplug. With the fuel tank removed it is easy to change the OEM spark plugs by the NGK LKAR9BI9 (Iridium, substitutes stock Bosch VR6NEU).
This is why without changing anything else in the bike, after piggyback fuel management boxes upgrade, most of the times the top speed remains the same, although the mid range RPM (factory leaned to reduce emissions) behavior gets improved.
Regards!
