When are you guys making safley with 32lb injectors
11-18-2006, 01:21 AM
#1
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When are you guys making safley with 32lb injectors
I'm going to be doing a new h/c setup and shooting for around 420rwhp on motor and I was wondering if my 32lb injectors would be enough.
11-18-2006, 11:23 AM
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Injector size has to be based on flywheel HP, not on rwHP. Assuming your M6 has about 13% drivetrain losses, you will be shooting for 483 flywheel. Assuming a decent tune (0.465 BSFC), and limiting the injector duty cycle to 85%, you need an injector that can provide 32.7 #/HR at the pressure your fuel system operates at. A 32# SVO, rated at 39.15psi would provide what you need.... marginal, but they will work.
11-18-2006, 03:19 PM
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Injector size has to be based on flywheel HP, not on rwHP. Assuming your M6 has about 13% drivetrain losses, you will be shooting for 483 flywheel. Assuming a decent tune (0.465 BSFC), and limiting the injector duty cycle to 85%, you need an injector that can provide 32.7 #/HR at the pressure your fuel system operates at. A 32# SVO, rated at 39.15psi would provide what you need.... marginal, but they will work.
11-18-2006, 04:33 PM
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I've got 32lb injectors at stock fuel pressure in my mild 383. My injector duty cycle peaks at about 74% with the current setup. I don't know how your setup compares, and I don't have any dyno time on mine yet, so I don't know how useful that info is to you.
Last edited by Dave '97 Z28 M6; 11-18-2006 at 04:35 PM.
11-19-2006, 10:39 AM
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11-20-2006, 11:01 PM
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Well I did some calculations with my scanmaster and injector pulse width and I'm not even at 50% with my 32lb injectors making 375rwhp, so I should be fine with 420+rwhp, atleast I think I should be. I'm getting ~340 grams/sec on my MAF at the the shift point too, so I don't know how that calculates out.
11-21-2006, 09:50 AM
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Well I did some calculations with my scanmaster and injector pulse width and I'm not even at 50% with my 32lb injectors making 375rwhp, so I should be fine with 420+rwhp, atleast I think I should be. I'm getting ~340 grams/sec on my MAF at the the shift point too, so I don't know how that calculates out.
375rwHP / 0.83 = 431 flywheelHP
431 HP X 0.400 BSFC = 172.4 #/HR
172.4 #/HR / 8 injectors = 21.55 #/HR
21.55 #/HR / 0.50 DC = 43.1 #/HR
A 50% DC would require a 43.10#/HR injector. With a "good" tune you'll be running 0.44 BSFC, and that means you would need a 47.4 #/HR injector to stay under 50% DC.
Or, to put it another way, at 6000rpm, you would have to be seeing an injector pulse width of 10 mSec or less.
Last edited by Injuneer; 11-21-2006 at 09:55 AM.
11-21-2006, 10:52 AM
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Are you sure you used the formula I gave you for duty cycle correctly? There is no way a 32# injector, even running at 55psi (=38#/HR) can produce a DC of less than 50% at 375rwHP. Pick a ridiculously low BSFC like 0.400 #/HR/HP (NASCAR level), and you get:
375rwHP / 0.83 = 431 flywheelHP
431 HP X 0.400 BSFC = 172.4 #/HR
172.4 #/HR / 8 injectors = 21.55 #/HR
21.55 #/HR / 0.50 DC = 43.1 #/HR
A 50% DC would require a 43.10#/HR injector. With a "good" tune you'll be running 0.44 BSFC, and that means you would need a 47.4 #/HR injector to stay under 50% DC.
Or, to put it another way, at 6000rpm, you would have to be seeing an injector pulse width of 10 mSec or less.
375rwHP / 0.83 = 431 flywheelHP
431 HP X 0.400 BSFC = 172.4 #/HR
172.4 #/HR / 8 injectors = 21.55 #/HR
21.55 #/HR / 0.50 DC = 43.1 #/HR
A 50% DC would require a 43.10#/HR injector. With a "good" tune you'll be running 0.44 BSFC, and that means you would need a 47.4 #/HR injector to stay under 50% DC.
Or, to put it another way, at 6000rpm, you would have to be seeing an injector pulse width of 10 mSec or less.
I ran it up to 6500 RPM's and the right and left bank never got above 9mSec
I did it a few times too just to be sure.
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