Fueling calculations
Moderators: jsmcortina, muythaibxr
Fueling calculations
Hello, can anyone assist me with the proper equation for calculating the “required fuel” value?? I’ve recently overhauled my entire 93 Nissan ka24e engine to include bored piston holes .050 over, new connecting rod bearings, replaced intake with 240sx and I will, for the time being, use the oem injectors which if I remember correctly are 270cc top feed red tops. My old fuel pressure gauge crapped out so now I’m stuck using one that reads in bars only, not sure if this is better or worse yet. Any assistance would be greatly appreciated. Not exactly sure of the process for finding injector dead time either, it was a little easier while I had my Deatswerks 570cc injectors but I do not believe those would still work with this intake.
TunerStudio MS Lite! v3.1.08 (MS2/Extra 3.4.4 release 20201006 18:17BST(c)KC/JSM/JB PNP) EFI Simplified
93 Niss. Hardbody Pickup 4x4 ka24e-t (current project)
02 Sub. Impreza RS (extra project)
69 Street Legal Hon. Z50A (finished project)
69 340 Ply. Barracuda (future, long-term project)
93 Niss. Hardbody Pickup 4x4 ka24e-t (current project)
02 Sub. Impreza RS (extra project)
69 Street Legal Hon. Z50A (finished project)
69 340 Ply. Barracuda (future, long-term project)
Re: Fueling calculations
Try googling "Megasquirt Required Fuel calculation".
Re: Fueling calculations
Click the "Required Fuel..." button and it has a spot to input your known variables and it will calculate Req Fuel for you. All you need is:
- Engine displacement
- Cylinder count
- Injector rated flow at the fuel pressure you plan to run
- AFR for your selected fuel
Page 40:
https://www.msextra.com/doc/pdf/Megasqu ... Up-1.5.pdf
For dead times, see if you can find good data for your factory injectors, it might be out there.
If you want to kick it up a notch, you can test dead times yourself if you're able to build a small test stand.
Otherwise there are alternative methods of figuring out dead time, you can find them with a little bit of poking around.
- Engine displacement
- Cylinder count
- Injector rated flow at the fuel pressure you plan to run
- AFR for your selected fuel
Page 40:
https://www.msextra.com/doc/pdf/Megasqu ... Up-1.5.pdf
For dead times, see if you can find good data for your factory injectors, it might be out there.
If you want to kick it up a notch, you can test dead times yourself if you're able to build a small test stand.
Otherwise there are alternative methods of figuring out dead time, you can find them with a little bit of poking around.
Re: Fueling calculations
From MS1-Extra tuning manual:
Required Fuel – (Req_Fuel) this is top field of the Constants window. It has a calculation dialog to help you find an appropriate value. It should contain the injector pulse width, in milliseconds, required to supply the fuel for a single injection event at stoichiometric combustion and 100% volumetric efficiency.
Re-Scaling the VE and Req_Fuel - If you have already started tuning but feel your Req_fuel is making the VE table too big or small then you can change the Req_Fuel but you will need to re-scale the VE Table too or the whole table will be out by the percentage of the change in req_fuel so your engine will no run like it used to. Re-Scaling is acheived by going into Basic Settings - Fuel Table 1 then select Tools - VE Specific - Reset Req_Fuel
e.g. VE table full of very low numbers (idle is around 15 and WOT is around 60-70) but drives well and AFR's are correct, then try decreasing the req_fuel value.
In this example we have dropped the req fuel from 14.7 to 12.2, this is roughly a 18% decrease in size, so the whole VE table will be increased by 18% to compensate.
Required Fuel – (Req_Fuel) this is top field of the Constants window. It has a calculation dialog to help you find an appropriate value. It should contain the injector pulse width, in milliseconds, required to supply the fuel for a single injection event at stoichiometric combustion and 100% volumetric efficiency.
Re-Scaling the VE and Req_Fuel - If you have already started tuning but feel your Req_fuel is making the VE table too big or small then you can change the Req_Fuel but you will need to re-scale the VE Table too or the whole table will be out by the percentage of the change in req_fuel so your engine will no run like it used to. Re-Scaling is acheived by going into Basic Settings - Fuel Table 1 then select Tools - VE Specific - Reset Req_Fuel
e.g. VE table full of very low numbers (idle is around 15 and WOT is around 60-70) but drives well and AFR's are correct, then try decreasing the req_fuel value.
In this example we have dropped the req fuel from 14.7 to 12.2, this is roughly a 18% decrease in size, so the whole VE table will be increased by 18% to compensate.