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Basic math equation for this

SIZE=(BSFC)(HPCrank) / (duty cycle) (# Injectors)

BSFC: Basically breaks down to the ratio of FUEL to HP.
HPCrank: Horsepower at the crank.
Duty Cycle: DESIRED duty cycle (Try to keep it below 85%)
# Injectors: How many injectors you have on the engine.

NOTES: Typically a turbocharged BSFC will be between .50-.65 lb/hr-hp. This is dependent on the Volumetric Efficiency, the turbo and how well the EFI is tuned. I will be using .65 for 'wiggle room'. Horsepower will be 400. Duty Cycle will be 70 and 4 injectors will be used.



Now on to the math

1) SIZE= (.65x400) / (.70x4) = XX.X lb/hr
2) SIZE= (260) / (2.80) = XX.X lb/hr
3) SIZE = 92.85 lb/hr
4) convert lb/hr to CCs (92.85)(10.5) = ~975

So, as it is in this equation, if i want about a 400HP tC, I will need 1000cc injectors.

If you increase the duty cycle more you can work with smaller injectors.

Again, please remember that the BSFC will vary from car to car. If you stick with the .65 and a moderate duty cycle, you cant go wrong with this!

Quote:
Originally Posted by paul_dezod
Note that this is also contingent upon a consistent fuel pressure. Should you have a return pressure system with a rising rate FPR, your size injector needed will be less because as pressure increases, flow rate of injector increases.

MOST (not all) injectors are rated at ~44PSI OEM. (of course this changes from car to car, but thats something you can figure out on your own!)

What Paul said is completely true more PSI= smaller injectors.

THIS IS JUST AN EXAMPLE NOT NECCISARILY FOR THE TC!

New Pressure = (Old Press)(New Flow Rate)/(Old Flow rate) 2

NOTE: Hopefully you can understand this PEMDAS is required. Think back to High School or 8th grade math. Bold 2 means 'squared'

Say we want 450cc of flow from out 370cc injectors.

[(450/370)2 x 44]= New Pressure
450/370 =(1.216)2
(1.216)(1.216)= 1.478
(1.47) *(44)= 65 * Is multiply...cause itll put a smily in there

So if we want our 370cc injectors to flow like they are 450's we need 65PSI of fuel to flow.

 

http://rceng.com/technical.aspx

 

This thread is meant to be a help to our forums. More info in one spot= less time searching.

 

Note that this is also contingent upon a consistent fuel pressure. Should you have a return pressure system with a rising rate FPR, your size injector needed will be less because as pressure increases, flow rate of injector increases.

 

Awesome info... now I know that in order to efficiently achieve 280hp I need to swap up from the 440cc's that came with the S/C to 550cc injectors...

 

I have some 160lb in mine. Not sure if its overkill I want to make about 550whp we will see wut up soon.

 

rising rate FTW, makes it harder to tune (if the vacuum source is not reliable) than constant fuel pressure. However, making over 400 crank on 440cc injectors is rather astounding

 

also consider how the manufacturer rated their injectors, it might be possible for them to rate an injector at higher fuel pressure to bump up the numbers "CC". If you have the psi rating available then check it coz you could be misled. Most use the 3 bar pressure though which is pretty much standard.

 

^ correct indeed I keep the suggestions on what needs to be added. More input = more information I can put in to help more people!

If you guys want I can do a tC only, then most of the guessing will be taken out. LMK what you want guys!

 

No inputs? Going to get the next batch typed up and the info put into one post.