ok this is my setup i have a 94 hatch with a b20 swap. i have also put a b16 head on it along with valve springs high comp. valves and titanium retainers. in the bottom end i have wisco pistons 12.5:1's and eagle h beam rods. i also have a s2000 fuel pump and fuel pressure reg and vafc

my question is what size injectors would be good for a high shot of nitrous (like a 100 shot) and what else would need to be done to the engine it self.


any info would be great thanx.

quick question...wut are u using to tune this thing

my question is what size injectors would be good for a high shot of nitrous (like a 100 shot) and what else would need to be done to the engine it self.
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you want to do some math to get some correct information.

brake-specific-fuel consumption (BSFC) is the formula used for calculating fuel flow. The lower the number the more efficient the injector is.

A rule of thumb is is a gasoline engine will have a BSFC of around 0.40 to 0.60.
N/A motors having 0.45-0.50 and Turbo engine's having 0.55-0.60 or higher.

Examples:

This formula used on an engine that produced 350hp with a BSFC of 0.45

To determine the fuel pump flow you do some math.
(350 x 0.45) + (350 x 0.45 x .25) = 157.5 = 39.375 = 196.8 lb-hr (the .25 being extra insurance).

So that engine would require a fuel pump with the flow rating of atleast 196.8 lb-hr.

Ok so we can establish a formula of
HP= 350
BSFC= .045
350 x 0.45 = 157.5

The engine will require 157.5 lb-hr or fuel flow it's lower than what is needed for the fuel pump because of the extra .25 added on for insurance.

Low impedance injectors are typically measure 2 ohms and are used in high performance application's because of their faster response time.

So the vehicle we have is a 4 cylinder engine with 4 low impedance injectors that have an impedance of 2.0, power that peaks at 7,000 rpm and a BSFC of 0.45 now you can determine the correct injector size for the engine.

A few other terms used are:
Total Fuel Flow Requirement (TFFR)
Uncorrected Injector Size (UIS)
Available Injection Time (AIT)
Injection Recovery Time (IRT)
Maximum Duty Cycle (MDC)

Formulas:

HPxBSFC = TFFR
TFFR/Number of injectors = UIS
60,000/7,000rpm = AIT
(AIT - IRT)/ AIT = MDC
UIS/MDC = required injector size

Now plug in some numbers:
TFFR = 350 x 0.45 = 157.5 lb-hr
UIS = 350/4 = 39.37 lb-hr
AIT = 60,000/7,000 = 8.571 ms
MDC = (8.571-2.0)/8.571 = 0.7666
required injector size = 39.37/0.7666 = 51.35 lb-hr

and to convert lb-hr to cc-min, take 51.35 and mulitply that by a factor of 10.50 and you get 539 cc-min so the proper size injector's for this application would be 540cc or 550cc injectors.

To get the correct size injector's for the amount of HP you are running without the Fuel pump mathmatics you can do this.

Say the target HP rating at the crank is 200 so you multiply that by the BSFC which let's say is 0.50 *turbo motor* = 100

200 x 0.50 = 100

Then the number of injectors (4) multiplied by the Injector Duty Cycle (0.80) = 3.2

4 x 0.80 = 3.2

Then you divide 100 into 3.2 which equals 31.25

100/3.2 = 31.25

Then you do the conversion from lb-hr to cc-min

so you get

31.25 x 10.50 = 328cc-min.

Hope this help's some!

yes this dose help thanx.

Holy shit, Civichbsi91 that was a nice reply, it also helped me learn some stuff, nice job.

thank's, I was bored at like 5 in the morning so I decided to do alittle like write up kinda thing :)