Dumb Question
Burning Brakes
Joined: Oct 2008
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From: Orono, Ontario
Thread Starter
Burning Brakes
Joined: Feb 2002
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From: Jasper GA
A follow-up question: can injectors operate at greater than 100% duty cycle? I'm asking because using the linked injector sizing formula, my engine does not seem to have been capable of making the dyno numbers that the sheet from my builder/tuner showed. Specifics: forged 427, LS7 heads, F1C at 8 psi, 60 lb/hr injectors, no meth, 798 RWHP @ 6000 rpm.
Safety Car
Joined: Jan 2008
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From: Boise
Depends on who you talk to and how they are set up. Once you get passed 95% they have a very good possibility of going static.
Most people consider 85% maxed out on injectors, but these new injectors are so linear they can usually be run all the way up to 100% no problems
Most people consider 85% maxed out on injectors, but these new injectors are so linear they can usually be run all the way up to 100% no problems
Racer
Joined: Jan 2010
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A follow-up question: can injectors operate at greater than 100% duty cycle? I'm asking because using the linked injector sizing formula, my engine does not seem to have been capable of making the dyno numbers that the sheet from my builder/tuner showed. Specifics: forged 427, LS7 heads, F1C at 8 psi, 60 lb/hr injectors, no meth, 798 RWHP @ 6000 rpm.
With a 346 at 10lbs and single nozzle meth I am 88% on 60lb injectors
640 dynojet/550 mustang
Last edited by 2bridges; Mar 19, 2013 at 01:46 PM.
Supporting Vendor
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I don't know how much I believe the calculation in HPT. I've been running over 111% DC for years with no issues.
According to the math the numbers are correct-but when the injector is scaled for stay under a harcoded limit who know's what's true anymore.
According to the math the numbers are correct-but when the injector is scaled for stay under a harcoded limit who know's what's true anymore.
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Melting Slicks
Joined: Jul 2008
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From: Houston Texas
2018 Corvette of Year Finalist
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And what happens when you enter artificial VE numbers? I'm spraying so much meth that all my VE numbers in the full boost area are less than 100%. I'm backing fuel out to keep from being too rich due to the volume of meth.
Melting Slicks
Joined: Feb 2006
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From: Houston
IDC is just looking at pulse widths and RPM. I believe the HPT readings stay accurate even with scaling. No reason not too.
At 100% the injector is being told to stay open all the time. Doesn't leave any room for error. I like the 85% rule, but it needs to be in somewhat cool weather. Don't want to lean out when it gets cold.
110% IDC means the injector is being told to pulse more than it is capable of.
At 100% the injector is being told to stay open all the time. Doesn't leave any room for error. I like the 85% rule, but it needs to be in somewhat cool weather. Don't want to lean out when it gets cold.
110% IDC means the injector is being told to pulse more than it is capable of.
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IDC is just looking at pulse widths and RPM. I believe the HPT readings stay accurate even with scaling. No reason not too.
At 100% the injector is being told to stay open all the time. Doesn't leave any room for error. I like the 85% rule, but it needs to be in somewhat cool weather. Don't want to lean out when it gets cold.
110% IDC means the injector is being told to pulse more than it is capable of.
At 100% the injector is being told to stay open all the time. Doesn't leave any room for error. I like the 85% rule, but it needs to be in somewhat cool weather. Don't want to lean out when it gets cold.
110% IDC means the injector is being told to pulse more than it is capable of.
I'm making some JAM I know-but not that much!
Melting Slicks
Joined: Jul 2008
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From: Houston Texas
2018 Corvette of Year Finalist
2017 C5 of Year Finalist
Here's an equation I found for injector duty cycle:
Inj duty(%) = pulsewidth*(rpm/1200)
Example:
109% = 21.5ms * (6100rpm/1200)
I'll check and see how mine compares.
Inj duty(%) = pulsewidth*(rpm/1200)
Example:
109% = 21.5ms * (6100rpm/1200)
I'll check and see how mine compares.
Thread Starter
Burning Brakes
Joined: Feb 2002
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From: Jasper GA
My next concern is where my tuner is taking me now. He's installing a dual nozzle meth system and going from the current 5" blower pulley down to 4.25" with the goal of 13-14 psi, and plans to upgrade the injectors to 80 lb/hr. Given the earlier commentary, this still seems too small.
BTW, I'm not running unusually high fuel pressure.
BTW, I'm not running unusually high fuel pressure.
Supporting Vendor
Joined: Nov 2012
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Supporting Vendor
Joined: Nov 2012
Posts: 1,123
Likes: 3
My next concern is where my tuner is taking me now. He's installing a dual nozzle meth system and going from the current 5" blower pulley down to 4.25" with the goal of 13-14 psi, and plans to upgrade the injectors to 80 lb/hr. Given the earlier commentary, this still seems too small.
BTW, I'm not running unusually high fuel pressure.
BTW, I'm not running unusually high fuel pressure.
buy once & done
Melting Slicks
Joined: Feb 2006
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From: Houston
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 1,154
Likes: 25
From: Jasper GA
1000cc injectors seemed to me to be a better answer, but my shop has done me right over the past few years, so I'm avoiding second guessing them. I may end up doing the upgrade twice, depending on how things play out over the next few days.