Nistune Forums

Im finding some inconsistancies with injector sizing. Nistune resizes injector k-values differently than what I have been finding in "real-world"
tunes. For instance I found these sizing calculations below on twinturbo.net:

For 370cc injectors use a K-value of ~ 288
For 440cc injectors use a K value of ~ 235
For 555cc injectors use a K-value of ~ 208
For 740cc injectors use a K-value of ~ 160
For 850cc injectors use a K-value of ~ 134

Dual intake, single MAF: double the K-value.

Now when I do the conversions in Nistune from 288 -> 740 I get a k-value
of 144. That actually makes sense because the injectors are twice the size of stock injectors (370cc). In "real-world" bins I have been seeing k-values of 310, 323, and 340 for 740cc injectors with dual intakes. My Z runs rough with a 288 k-value (144 x 2) but runs pretty smooth with the 340 k-value. Can anyone help me make sense of whats going on? How do I go about really getting my ecu fine tuned for 730's which is what I actually have? Right now Im running 325 k-value thats running lean at idle (16-17 afr) and misfires a little bit but runs great when the engine is fully warmed up.

we use a 'theoretical' calculation at best. bigger injectors are more prone to not get it quite right

basically we adjust K by mutiplying old / new injector size

but we dont account for the Z32 of adjusting for dual intakes where you need to multiply that yourself

the idea was to get the ECU to a starting point. maybe using some reference values we can fine tune these a bit but you really need to tune them in properly along with latency

also look at Petes tuning guide to get your K constant right (its on the documentation page). have you gone through this at running temperature?

after that once K is sorted any cold start issues can be sorted out in other tables afterwards