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Pampered-Z · 03-25-2010, 11:34 AM

You are probably not getting a true 36 out of the injectors. You need more fuel which is why you are so far over the duty cycles. FP isn't really going to overcome that.

Below is the formulal I use for my car. This is from my Electromitive DFI, I shortened some of the text! Plugging in you numbers I come up 34 lb injectors.

1) Knowledge of the break specific fuel consumption of your engine at maximum output, values can be from .39 (lean and efficient) to .69 (inefficient cumbustion chambers and lots of boost). Example of how to determine the fuel requirement of an engine with the a BSFC of aproximately .53.

500 HP x .53 BSFC = Fuel requirement of 318 lb/h

2. How many fuel injectors are being used? This is pretty obvious, we need to know the per injector fuel requirement.

318 lb/h divided by 8 injectors = 39.75 lb/h per injector

3. At what RPM are we making this power? This is probably where most people get stuck. Not unless you are being so crude as to run your injectors at 100 % duty cycle, can you make do with injectors sized exactly by the lb/h per injector number. A fuel injector needs a certain amount of time to recover from being engaged between spraying events. It is important to know when your injector fires for this step, but let us
assume the injector fires once per engine revolution, just like ELECTROMOTIVE's phased sequential injection for multi-point systems. The engine speed for our ongoing example will be 7,600 RPM, and we need to know how much time there is between injector events.

60,000 ms (one minute) divided by 7,600 RPM= 7.8947 ms between Top Dead
Centers

4. What is the % of duty cycle that can be used at this point? This is determined by the time it takes the injector to close after it has been opened, which is usually somewhere around 1 ms. Here we need to know the ratio between the total amount of time available and what we can actualy use.

7.8947 ms - 1ms = 6.8947 ms 6.8947 ms / 7.8947 ms = 0.8733 or 87.33%

5. Injector Size Requirement! Now we have all the info required to select an injector.
Fuel Requirement of 39.75 lb/h divided by the maximum duty cycle of 87.33% = 45.5 lb/h
With this information we can now go get an injector.

So plugging in your information:

460hp x .53 = 243.8

243.8 / 8 = 30.475 (Fuel required)

RPM = 6400

60,000 ms / 6400 RPM = 9.375 Ms - BTDC

9.375 - 1ms = 8.375 ms | 8.375 / 9.375 = 0.8933

30.475 (fuel) / 0.8933 (Duty cycle) = 34.11 Fuel Injector size.

From this your 30s are too small, you need 36s to stay in the 80% duty cycles.

03-25-2010, 11:34 AM	#6
Pampered-Z Sliderule / Moderator Join Date: Oct 2004 Location: Catawissa PA Posts: 2,294 iTrader: (1)	You are probably not getting a true 36 out of the injectors. You need more fuel which is why you are so far over the duty cycles. FP isn't really going to overcome that. Below is the formulal I use for my car. This is from my Electromitive DFI, I shortened some of the text! Plugging in you numbers I come up 34 lb injectors. 1) Knowledge of the break specific fuel consumption of your engine at maximum output, values can be from .39 (lean and efficient) to .69 (inefficient cumbustion chambers and lots of boost). Example of how to determine the fuel requirement of an engine with the a BSFC of aproximately .53. 500 HP x .53 BSFC = Fuel requirement of 318 lb/h 2. How many fuel injectors are being used? This is pretty obvious, we need to know the per injector fuel requirement. 318 lb/h divided by 8 injectors = 39.75 lb/h per injector 3. At what RPM are we making this power? This is probably where most people get stuck. Not unless you are being so crude as to run your injectors at 100 % duty cycle, can you make do with injectors sized exactly by the lb/h per injector number. A fuel injector needs a certain amount of time to recover from being engaged between spraying events. It is important to know when your injector fires for this step, but let us assume the injector fires once per engine revolution, just like ELECTROMOTIVE's phased sequential injection for multi-point systems. The engine speed for our ongoing example will be 7,600 RPM, and we need to know how much time there is between injector events. 60,000 ms (one minute) divided by 7,600 RPM= 7.8947 ms between Top Dead Centers 4. What is the % of duty cycle that can be used at this point? This is determined by the time it takes the injector to close after it has been opened, which is usually somewhere around 1 ms. Here we need to know the ratio between the total amount of time available and what we can actualy use. 7.8947 ms - 1ms = 6.8947 ms 6.8947 ms / 7.8947 ms = 0.8733 or 87.33% 5. Injector Size Requirement! Now we have all the info required to select an injector. Fuel Requirement of 39.75 lb/h divided by the maximum duty cycle of 87.33% = 45.5 lb/h With this information we can now go get an injector. So plugging in your information: 460hp x .53 = 243.8 243.8 / 8 = 30.475 (Fuel required) RPM = 6400 60,000 ms / 6400 RPM = 9.375 Ms - BTDC 9.375 - 1ms = 8.375 ms \| 8.375 / 9.375 = 0.8933 30.475 (fuel) / 0.8933 (Duty cycle) = 34.11 Fuel Injector size. From this your 30s are too small, you need 36s to stay in the 80% duty cycles. __________________ 93Z M6 Black: The 385 Lives! Supercharged, 3-core front mount intercooler, GTP heads, 3:73's, Street twin clutch, Jethot Longtubes, Mufflex 4" catback/spintech, S+W cage, Spohn Suspenion, Yada Yada Yada 1) Build it 2) Race it 3) Break it 4) Repeat!!! Last edited by Pampered-Z; 03-25-2010 at 11:41 AM.