i recently did a swap from 680cc (gslse) injectors to 7500c (Siemens). my fuel pressure key on, engine off is 40 psi,
since swapping injectors my fuel map has been leaner then usual under cruise. (havent boosted yet)
sometimes reaching 16 afr.
i heard 680cc are rated at around 37 psi
while 750cc at 43.5 psi

is that a problem that im still running them at 40 psi instead of 43.5?

 

In theory, the 750cc injectors should have improved the flow rate a little bit, assuming your 680cc injectors were also running at 40psi fuel rail pressure.

680cc@37psi = 707cc@40psi
750cc@43.5psi = 719cc@40psi

If you would ever like to run the numbers yourself, the equation is Revised Static Flow = (Original Static Flow * sqrt(Revised Pressure / Original Pressure)).

Manufacturers may use different methods to rate their injectors (test fluid vs. gasonline, rounding of numbers, etc.), and the efficiency of the spray pattern can vary depending on the duty cycle, pressure, etc., so there can still be some factors not addressed by the above formula.

If your fuel pump is up to it, you can slightly increase the fuel rail pressure to see if that helps. Most fuel injectors flow well up to 4 bar (58psi), so you have more than enough room to play with.

 

not sure y my maps are leaner then before. possable vac leak?