How much HP can stock fuel injectors hold?
09-28-2006, 10:55 AM
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How much HP can stock fuel injectors hold?
Still trying to diagnose my high RPM miss and the shop thinks that my injectors can't handle the HP I am making. He plugged my horsepower(390rear wheel) into his calculator with 22lb injectors and 45psi fuel pressure and it said that I would be running at 100% duty cycle at 360 rear wheel hp... So could this be my problem or was he plugging in incorrect numbers on his calculator?? As always any imput is appreciated. Thanks.
09-28-2006, 11:34 AM
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Re: How much HP can stock fuel injectors hold?
Stock 95 injectors are nominally rated at 24 #/HR at 43.5psi. They are programmed in the PCM at 24.9 #/Hr.
Assuming an 0.46 BSFC and a limit of 90% on the duty cycle, you can support about 390 flywheel HP with the stockers. At 100% and 45.0psi you could push 440 flywheel HP, but the injectors will not perform reliably at 100% DC.
In theory, if you really have 22 #/HR injectors, you can't be making 390rwHP. That would be 448 flywheel (at 13% drivetrain loss), and a 22 #/Hr injector at 45psi would be at 115% DC.
Assuming an 0.46 BSFC and a limit of 90% on the duty cycle, you can support about 390 flywheel HP with the stockers. At 100% and 45.0psi you could push 440 flywheel HP, but the injectors will not perform reliably at 100% DC.
In theory, if you really have 22 #/HR injectors, you can't be making 390rwHP. That would be 448 flywheel (at 13% drivetrain loss), and a 22 #/Hr injector at 45psi would be at 115% DC.
09-28-2006, 05:15 PM
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Re: How much HP can stock fuel injectors hold?
If your injectors are at their limits and causing a miss/knock/etc it will definitely show in the AFR. Got a Wide band to hook up and see if you're going lean in the higher rpms? If so, then increase the WOT fueling above 5k rpms and if the AFR doesn't change, you are definitely at the end of your injectors. If you are in fact putting down 390rwhp, you're out.
Mine starts to go lean at around 5200 rpms and at about 340rwhp with the stock injectors.
Mine starts to go lean at around 5200 rpms and at about 340rwhp with the stock injectors.
09-28-2006, 08:10 PM
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Re: How much HP can stock fuel injectors hold?
Thats gotta be what my problem is..... The shop has a set of Z06 28.8lb injectors they are willing to let me HAVE and they say that they will fit. Are they correct?
09-29-2006, 08:36 AM
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Re: How much HP can stock fuel injectors hold?
The LSx family of engines uses 58psi fuel pressure. A 28.8 #/HR LSx injector running at 43.5psi is only going to flow the exact same amount as a stock LT1 24 #/HR injector. Hard to believe they only put a 28.8# injector in a Z06. That's the size they used in the first few years of the LS1 (then went to 26.5)
09-29-2006, 04:05 PM
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Re: How much HP can stock fuel injectors hold?
Originally Posted by Injuneer
The LSx family of engines uses 58psi fuel pressure. A 28.8 #/HR LSx injector running at 43.5psi is only going to flow the exact same amount as a stock LT1 24 #/HR injector. Hard to believe they only put a 28.8# injector in a Z06. That's the size they used in the first few years of the LS1 (then went to 26.5)
So what would I need to do in my situation? Get an adjustable fuel pressure regulator?
09-29-2006, 04:24 PM
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09-29-2006, 05:08 PM
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Re: How much HP can stock fuel injectors hold?
Estimate your FLYWHEEL HP, now if you're done, or after you make some more mods in the future. Then multiply the FLYWHEEL HP by 0.07 to get the minimum injector size. Example:
500 flwyheel HP X 0.07 = 35 #/HR
500 flwyheel HP X 0.07 = 35 #/HR
09-29-2006, 09:11 PM
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Re: How much HP can stock fuel injectors hold?
Its weird Ive been on this board for a very long time and I thought that I had all my bases covered when it came to my rebuild... I guess I just simply overlooked the injectors... So would I need to mess with my fuel pressure or just get bigger injectors?
09-30-2006, 10:31 AM
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Re: How much HP can stock fuel injectors hold?
Originally Posted by 1997blackz28
will the stock fuel pump flow enough for a set of 30# injectors?
I have the Racetronix 255 setup. So does anybody know if I need to up the fuel pressure or not? And if so what should I up it to?
09-30-2006, 10:54 AM
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Re: How much HP can stock fuel injectors hold?
Originally Posted by 95z28 -quicksilver
I have the Racetronix 255 setup. So does anybody know if I need to up the fuel pressure or not? And if so what should I up it to?
You can buy a set of 36#/HR injectors (flow rated at 43.5psi), install them, have the flow constant set at ~36.0 in the PCM, and do NOTHING to the fuel pressure.
Or, if you wanted to play games with injector sizes, you could by a set of 32#/HR injectors (flow rated at 43.5psi), crank the fuel pressure to 55psi, and have the flow constant set at ~36.0 in the PCM.
Works either way. Most people by the right size injector, and leave the fuel pressure at stock.