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# How to know the size for the current injector

### Tech Articles

Discussion and questions related to the course EFI Tuning Fundamentals

To ensure if I understand this process, what is the size of the injector that is fitted to my engine? Let's assume if we have Nissan VK56DE engine,338.8 ci,5552 cc, V8, target A/F 14 and RPM 7000 (what does that mean? does it mean it will show me the result only for this specific range of 7000 RPM or it will give the result for the all site, example: 1000,2000,3000 etc... Rpm and so on until reach 7000 RPM?).

1) Airflow= 338 * 3500 / 1728

= 684.6 CFM

2) Air density= 2.7 * (14.7 / 521)

= 0.076 Ib/in

3) Mass air flow= 684.6 * 0.076

= 52 Ib/min

4) Mass air flow per cylinder= 52 / 8

= 6.5 Ib/min

5) Required fuel flow= 6.5 / 14

= 0.46 Ib/min

6) Cycle time= 120 / 7000

= 0.017 = 17 msec

7) Injector duty cycle= (0.46 / 1) *100

= 46 %

8) Injector puls width= 17 * 0.46

= 7.82 msec

9) Correction factor= 13.5 / 14

= 0.96 = 96 % VE

So now I'm using a Motec m800 and I want to fill the Injection setup table. What is the Injector pulse width number that I have to put it in the table? Is it what I found it in step no 8 that it will be 7.82 msec or no?

- My question is what is the actual size of my injector that the OEM are using for the current engine? ( I don't have the data for the current injector, so I'm trying to find it by my self by using your equation )

Note:

In another way can we use these equations to find the size of injector.

Let's say 5552 cc / 8 cylinders = 694? So, what does that mean?

We usually reply within 12hrs (often sooner)

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