When tuning for larger injectors, the fuel injector constant must be scaled appropriately. You'll notice the injector constant in Domino Tuning Suite is the raw number (not a value which represents something in cc/min or lb/hr). The stock value for a M3 is 43478 which corresponds to 16lb injectors (rated at 3.0b). Assuming you're swapping to 24lb injectors (also rated at 3.0b), you'll need to scale the injector constant by the same ratio.
- 16 / 24 = 0.667
- 0.667 * 43478 = 28985
If your injectors are rated at a different pressure, you'll have to adjust accordingly. There are many calculators available online to help determine this.
Additionally, every value that references engine load must be scaled by the same factor. This includes any value within the body of a table, axis, or single constants. There are many references to engine load in the OBD1 DME, so these files are a good starting point!
This methodology of scaling works well for injectors up to 42lb. When tuning for injectors larger than this, additional techniques must be used which are described in later posts below.
Attached below are some base tunes for 24lb injectors (rated at 3.0b fuel pressure). This should cover any N/A modifications and low boost (less than 6psi) F/I applications. There is also a 42lb tune attached below which could be the starting point for a turbo tune.
Warning: The only thing that has been changed with these tunes is scaling for generic 24lb injectors. Some slight tuning may still be necessary to the injector constant to dial in your specific injectors, even if they're 24lb. Other tweaks will also need to be made to the fuel tables to run perfectly. These tunes should only be used as a starting point!
Note that these tunes have been scaled assuming that larger injectors are the only modification done to the vehicle. If your vehicle has forced induction, then modifications will have to be made to the load axes on the fuel and ignition tables where additional room for extra load is needed. Also note that the maximum MAF controls have not been touched in these base tunes. Until these are scaled appropriately for forced induction, fuel cuts could be applied at higher engine speeds.