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Fuel Injectors! Which One For You?

wasnt me

By wasnt me,
in Tutorials / DIY / FAQ

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wasnt me Collaborator

wasnt me

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All right guys i thought i would put up a little guide to help out with choosing the right size fuel injector.

So i see alot of guys asking what size injectors they need to make x amount of power. with a few simple calculations its easy to find out exactly how much injector you will need..

Things you need to know before srating.

Fuel going to be used (PULP or E85).

Naturally aspirated or forced induction.

How many Injectors being used.

For this example i will work on 350rwkw, turbo, PULP fuel, 6 cylinder as the target amount of power.

Target Injector duty cycle will be 80% and rail pressure 43.5psi

First thing we need to know is how many bhp is 350rwkw?

350 multiply by 1.36 = 476bhp.

Next we need to work out your B.S.F.C (Brake Specific Fuel Consumption)- How much fuel your car uses per horse power per hour. See Below. (every car is different but this will help as a general rule)

Naturally Aspirated PULP = .5

Naturally Aspirated E85 = .62

Forced Induction PULP = .7

Forced Induction E85 = .9

now to find out what size injectors we need!!!!

HORSEPOWER X B.S.F.C 476 X .7 ___________________ = __________________ = 69.4LB/HR

NO. OF INJECTORS (6) X .8 4.8

(DUTY CYCLE)

To convert LB/HR to CC/MIN Multiply by 10.5 = 728cc.

so 729cc at 43.5psi rail pressure. so now we have got ourself some 750cc injectors, Now lets work out what sort of cc we can get out of these injectors with a little extra Base rail pressure!!!!!!

Considering most injectors will have a max pressure of 100psi we can push these injectors a lot harder then they are currently work.

Since we are running forced induction and using a rising rate FPR we have to factor in the boost pressure being used. Lets say 20psi. so 43.5psi(Base Rail pressure) plus the 20psi boost pressure equals 63.5psi. So an extra 10psi Base rail pressure should be no problem for these injectors.

(Always calculate the flow rates on the base rail pressure. the rising rate is there to counteract the pressure from in inside if the runners pushing back against the injector)

NEW FUEL PRESSURE (50PSI)

_________________ = 1.15 FIND THE SQUARE = 1.07 MULTIPLY BY = 802CC

ROOT OF THIS NUMBER OLD CC (750)

OLD FUEL PRESSURE (43.5PSI)

This is a guide only. it is also best to check with your tuner when buying injectors,

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https://www.sau.com.au/forums/topic/350429-fuel-injectors-which-one-for-you/
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