Injector flow rate 43.5psi VS 58psi and how it effects injector duty cycle.
04-02-2008, 02:18 AM
#1
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Injector flow rate 43.5psi VS 58psi and how it effects injector duty cycle. ok you have and injector rated at 43.5psi IE racetronix's new 79l# hr injector, and you use the spread sheet and our stock rail pressure is 58psi. according to the spread sheet it acts like a 91# injector. question is if its rated at 43.5psi and we run 58psi what does that do to the injector duty cycle???
what would happen to the motor if i ran 43.5psi w/ an external FP regulator. the scaled the injectors to what they are rated at???? would the injector duty cycle go past 80% w/ a 900hp motor??? Same question if rail pressure was regulated to 58psi...
thanks..
what would happen to the motor if i ran 43.5psi w/ an external FP regulator. the scaled the injectors to what they are rated at???? would the injector duty cycle go past 80% w/ a 900hp motor??? Same question if rail pressure was regulated to 58psi...
thanks..
04-02-2008, 11:08 AM
#2
Take the square root of your pressure divided by the rated pressure. Multiply that amount by the flow at the rated pressure.
((58/43.5)^(1/2))*79 = 91.22
Duty cycle will be lower at 58# than at 43.5#, because your injectors are flowing more fuel in a given period of time at the higher pressure.
Your injectors need to be scaled to whatever fuel pressure you are running.
Running at the lower 43.5# is easier on the fuel pump, due to the inverse relationship between flow and pressure, as long as your injectors can support your horsepower requirements at the lower pressure.
Another rough rule of thumb is injector # per hour * number of injectors * 2 = max hp capacity
Example: 79*8*2=1264hp
This roughly estimates your fueling capacity in crankshaft horsepower. Adjust downward to account for desired duty cycle (and drive line loss if calculating based on rear wheel horsepower).
((58/43.5)^(1/2))*79 = 91.22
Duty cycle will be lower at 58# than at 43.5#, because your injectors are flowing more fuel in a given period of time at the higher pressure.
Your injectors need to be scaled to whatever fuel pressure you are running.
Running at the lower 43.5# is easier on the fuel pump, due to the inverse relationship between flow and pressure, as long as your injectors can support your horsepower requirements at the lower pressure.
Another rough rule of thumb is injector # per hour * number of injectors * 2 = max hp capacity
Example: 79*8*2=1264hp
This roughly estimates your fueling capacity in crankshaft horsepower. Adjust downward to account for desired duty cycle (and drive line loss if calculating based on rear wheel horsepower).
Last edited by RAACCR; 04-02-2008 at 11:23 AM.
04-02-2008, 12:36 PM
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Take the square root of your pressure divided by the rated pressure. Multiply that amount by the flow at the rated pressure.
((58/43.5)^(1/2))*79 = 91.22
Duty cycle will be lower at 58# than at 43.5#, because your injectors are flowing more fuel in a given period of time at the higher pressure.
Your injectors need to be scaled to whatever fuel pressure you are running.
Running at the lower 43.5# is easier on the fuel pump, due to the inverse relationship between flow and pressure, as long as your injectors can support your horsepower requirements at the lower pressure.
Another rough rule of thumb is injector # per hour * number of injectors * 2 = max hp capacity
Example: 79*8*2=1264hp
This roughly estimates your fueling capacity in crankshaft horsepower. Adjust downward to account for desired duty cycle (and drive line loss if calculating based on rear wheel horsepower).
((58/43.5)^(1/2))*79 = 91.22
Duty cycle will be lower at 58# than at 43.5#, because your injectors are flowing more fuel in a given period of time at the higher pressure.
Your injectors need to be scaled to whatever fuel pressure you are running.
Running at the lower 43.5# is easier on the fuel pump, due to the inverse relationship between flow and pressure, as long as your injectors can support your horsepower requirements at the lower pressure.
Another rough rule of thumb is injector # per hour * number of injectors * 2 = max hp capacity
Example: 79*8*2=1264hp
This roughly estimates your fueling capacity in crankshaft horsepower. Adjust downward to account for desired duty cycle (and drive line loss if calculating based on rear wheel horsepower).
Looks like a 79# would be good to about 850-900 whp and a 91# would be good to about a 1000 whp using those calc. at 80% DC and 15% drivetrain loss.
Dan
04-02-2008, 01:00 PM
#4
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could I run my ls1 at 43.5 psi (since the racetronix 79# are rated at 43.5psi) w/a front mount regulator that has a return??? so it would be easier to tune..
this is for my dry nitrous kit.
this is for my dry nitrous kit.
04-02-2008, 07:21 PM
#5
Yes you can. You would need to scale your tune to the injector flow rate @ 43.5#. Injector scale should be mapped accordingly if your regulator is set-up to run 43.5# constant vs. boost/vacuum referenced.
04-02-2008, 11:47 PM
#7
Actually that'd be manifold referenced.
Here's a plus to doing it that way. At WOT, you get full pressure, but pressure is incrementally pulled back against MAP vacuum everywhere below. With it pulling like this, idle fuel pressure will be lower making idle tuning a bit easier. Also, your IFR table will be a flat line since flow will be constant against the MAP. Nice.
Here's a plus to doing it that way. At WOT, you get full pressure, but pressure is incrementally pulled back against MAP vacuum everywhere below. With it pulling like this, idle fuel pressure will be lower making idle tuning a bit easier. Also, your IFR table will be a flat line since flow will be constant against the MAP. Nice.
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04-04-2008, 06:03 AM
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Actually that'd be manifold referenced.
Here's a plus to doing it that way. At WOT, you get full pressure, but pressure is incrementally pulled back against MAP vacuum everywhere below. With it pulling like this, idle fuel pressure will be lower making idle tuning a bit easier. Also, your IFR table will be a flat line since flow will be constant against the MAP. Nice.
Here's a plus to doing it that way. At WOT, you get full pressure, but pressure is incrementally pulled back against MAP vacuum everywhere below. With it pulling like this, idle fuel pressure will be lower making idle tuning a bit easier. Also, your IFR table will be a flat line since flow will be constant against the MAP. Nice.
