Fuel injectors, duty cycle and how not to look like an idiot. **please read**
11-21-2007, 09:29 AM
#1
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Fuel injectors, duty cycle and how not to look like an idiot. **please read**
It's too bad those profiting off of content provided to their site for free don't appreciate the service.
Last edited by PirateMcFred; 03-12-2012 at 06:33 AM.
11-21-2007, 09:48 AM
#2
Pirate, just to add.
The pulse width is the raw number of milliseconds that the injector is open, and the duty cycle is just a calculation from that, when you add in rpm.
For instance:
Say you're at 8000rpm, in a 4 stroke engine, you fire the injector once every 2rpm, so take 8000/2 = 4000; 4000 / 60 = 66.66 rev/s; 1/66.66 = .015s or 15ms per revolution.
Now say that you need the injector open for 10ms to get enough fuel in.
10ms/15ms = 66.67% DC
Good info, I just noticed the guy on that G23 thread talking about something along these lines.
In that light, any duty cycle number you get from an online injector size calculator that is over 100% is just telling you that you need a bigger injector or more pressure. That can exist on paper, but not in the real world. Being over 100% duty cycle means that your injector needs longer than the length of one engine cycle at a given rpm to get enough fuel in.
Modified by mgags7 at 2:09 PM 11/21/2007
The pulse width is the raw number of milliseconds that the injector is open, and the duty cycle is just a calculation from that, when you add in rpm.
For instance:
Say you're at 8000rpm, in a 4 stroke engine, you fire the injector once every 2rpm, so take 8000/2 = 4000; 4000 / 60 = 66.66 rev/s; 1/66.66 = .015s or 15ms per revolution.
Now say that you need the injector open for 10ms to get enough fuel in.
10ms/15ms = 66.67% DC
Good info, I just noticed the guy on that G23 thread talking about something along these lines.
In that light, any duty cycle number you get from an online injector size calculator that is over 100% is just telling you that you need a bigger injector or more pressure. That can exist on paper, but not in the real world. Being over 100% duty cycle means that your injector needs longer than the length of one engine cycle at a given rpm to get enough fuel in.
Modified by mgags7 at 2:09 PM 11/21/2007
11-21-2007, 10:27 AM
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Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (PirateMcFred)
Duty cycle information in Crome tends to be wrong.
That's my 2c. I wish I knew it back in the day, maybe it will help out someone else
That's my 2c. I wish I knew it back in the day, maybe it will help out someone else
11-21-2007, 10:33 AM
#6
Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (A Blue Lude)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by A Blue Lude »</TD></TR><TR><TD CLASS="quote">Duty cycle information in Crome tends to be wrong.
That's my 2c. I wish I knew it back in the day, maybe it will help out someone else </TD></TR></TABLE>
The same goes for Hondata. The datalogger consistently reads out erratic numbers and sometime goes over 100% as well.
That's my 2c. I wish I knew it back in the day, maybe it will help out someone else
</TD></TR></TABLE>The same goes for Hondata. The datalogger consistently reads out erratic numbers and sometime goes over 100% as well.
11-21-2007, 10:54 AM
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Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (mgags7)
Excellent post, cleared up a few questions I had lingering 
Definite FAQ material.
Definite FAQ material.
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11-21-2007, 11:13 AM
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Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (PirateMcFred)
I think that's the way they're set up. Neptune's numbers are definitely arbitrary values, according to James/HRtuning.
11-21-2007, 11:48 AM
#9
Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (PirateMcFred)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PirateMcFred »</TD></TR><TR><TD CLASS="quote">I never thought that the cells in the fuel tables of Crome and hondata were ms pulse width values I always thought of the indicated value as arbitrary "fuel values."
*shrug*
</TD></TR></TABLE>
I'm not talking about the actual fuel table, though Blue might be, I'm just talking about the datalogger's numbers. It spits out DC % for you, and is often very wrong.
*shrug*
</TD></TR></TABLE>
I'm not talking about the actual fuel table, though Blue might be, I'm just talking about the datalogger's numbers. It spits out DC % for you, and is often very wrong.
11-21-2007, 12:46 PM
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Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (mgags7)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 »</TD></TR><TR><TD CLASS="quote">
I'm not talking about the actual fuel table, though Blue might be, I'm just talking about the datalogger's numbers. It spits out DC % for you, and is often very wrong.</TD></TR></TABLE>
I was referring to Crome's duty cycle table, which is claiming to tell you the actual duty cycle in %.
I found Hondata S200's DC log ok the one time I used it. It did spike to a 100% for no reason though
I'm not talking about the actual fuel table, though Blue might be, I'm just talking about the datalogger's numbers. It spits out DC % for you, and is often very wrong.</TD></TR></TABLE>
I was referring to Crome's duty cycle table, which is claiming to tell you the actual duty cycle in %.
I found Hondata S200's DC log ok the one time I used it. It did spike to a 100% for no reason though
11-21-2007, 04:17 PM
#11
* B A N N E D *
I stand corrected, thank you for the information Pirate. I myself was misinformed to begin with, as I kept reading about the dsm 450's in particular being risky of over working themselves at _hp level. But it does make perfectly good sense than an injector can't be over 100% duty cycle now that I think about it. However you didn't need to bash me or anything titling "how not to look like an idiot" that part I disagree with. The good information is what I'm after, not someone pointing fingers and such when I'm wrong, which is often because I still have alot to learn.
Anyhow, thanks for clearing this up for me. Looks like I'll be sticking with the 450's after all.
EDIT: Also, how exactly do you know when it's "time" for bigger injectors as far as upgrading things go? You run so much boost from one setup and are fine on one set of injectors, and then get something bigger and all of a sudden need bigger injectors? Duh, the answer is because you need more fuel at any given point in time, but what exactly determines that? And please don't call me a noob, atleast I'm asking legitimate questions here.
Anyhow, thanks for clearing this up for me. Looks like I'll be sticking with the 450's after all.
EDIT: Also, how exactly do you know when it's "time" for bigger injectors as far as upgrading things go? You run so much boost from one setup and are fine on one set of injectors, and then get something bigger and all of a sudden need bigger injectors? Duh, the answer is because you need more fuel at any given point in time, but what exactly determines that? And please don't call me a noob, atleast I'm asking legitimate questions here.
11-21-2007, 07:47 PM
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Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (98vtec)
how do you calculate what your current duty cycle in on your injectors??
11-21-2007, 07:56 PM
#14
* B A N N E D *
I'm not giving a direct answer because somehow it'll be wrong and false information, but it's in there towards the top of Pirates first post.
Think open/closed
Think open/closed
11-21-2007, 10:31 PM
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Re: (95greenlude)
you'd need to take the time between engine cycles at a given rpm and divide that by the corresponding pulsewith on your fuel map.
Matt's got it covered in his post where he states 15ms as the time between cycles at 8000 rpm, and 10ms being his pulsewidth = 66.67% duty cycle
Matt's got it covered in his post where he states 15ms as the time between cycles at 8000 rpm, and 10ms being his pulsewidth = 66.67% duty cycle
11-22-2007, 04:30 AM
#18
Re: (95greenlude)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 95greenlude »</TD></TR><TR><TD CLASS="quote">ok...so you need a tuning device....</TD></TR></TABLE>
Yeah. You *could* rig something up on the wires and keep a stock setup, but you'd have to buy an oscilloscope or something comparable in order to measure the pulse width, and those things are not cheap by any means.
Another thought I just had was, you could most likely use a high-end AC voltmeter to read duty cycle, some of them will actually measure it directly. But, you'd have to multiply the # you get from it by two because it would be measuring duty cycle for all 2 rotations of the engine between injector fires, when the duty cycle we calc is measured over just 1 rotation.
Yeah. You *could* rig something up on the wires and keep a stock setup, but you'd have to buy an oscilloscope or something comparable in order to measure the pulse width, and those things are not cheap by any means.
Another thought I just had was, you could most likely use a high-end AC voltmeter to read duty cycle, some of them will actually measure it directly. But, you'd have to multiply the # you get from it by two because it would be measuring duty cycle for all 2 rotations of the engine between injector fires, when the duty cycle we calc is measured over just 1 rotation.
11-22-2007, 05:34 AM
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Re: (mgags7)
OR the quick and dirty way to just get close would be to use the calculator at RCeng.com. you can backfigure duty cycle by using horsepower, injector size, pressure, brake specific #'s to get a close # if you are just trying to determine where you are at on injector size. obviously just an approximation though.
11-23-2007, 07:01 PM
#21
* B A N N E D *
Re: (ECX)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ECX »</TD></TR><TR><TD CLASS="quote">I stand corrected, thank you for the information Pirate. I myself was misinformed to begin with, as I kept reading about the dsm 450's in particular being risky of over working themselves at _hp level. But it does make perfectly good sense than an injector can't be over 100% duty cycle now that I think about it. However you didn't need to bash me or anything titling "how not to look like an idiot" that part I disagree with. The good information is what I'm after, not someone pointing fingers and such when I'm wrong, which is often because I still have alot to learn.
Anyhow, thanks for clearing this up for me. Looks like I'll be sticking with the 450's after all.
EDIT: Also, how exactly do you know when it's "time" for bigger injectors as far as upgrading things go? You run so much boost from one setup and are fine on one set of injectors, and then get something bigger and all of a sudden need bigger injectors? Duh, the answer is because you need more fuel at any given point in time, but what exactly determines that? And please don't call me a noob, atleast I'm asking legitimate questions here.
</TD></TR></TABLE>
Ahem.
Anyhow, thanks for clearing this up for me. Looks like I'll be sticking with the 450's after all.
EDIT: Also, how exactly do you know when it's "time" for bigger injectors as far as upgrading things go? You run so much boost from one setup and are fine on one set of injectors, and then get something bigger and all of a sudden need bigger injectors? Duh, the answer is because you need more fuel at any given point in time, but what exactly determines that? And please don't call me a noob, atleast I'm asking legitimate questions here.
</TD></TR></TABLE>Ahem.
11-23-2007, 07:09 PM
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Re: (ECX)
not exactly sure what you are asking but more power just needs more fuel so when the duty cycle starts to get up around 80% then its time for bigger injectors. an injector can only flow so much in a given amount of time so when thats not enough they just need to be bigger (flow more fuel) so they can flow more fuel in the same amount of time.
the injector calculator on RC's site works really well on determining how big of an injector you will need based off of h.p. goals and #of cylinders and fuel type used.
the injector calculator on RC's site works really well on determining how big of an injector you will need based off of h.p. goals and #of cylinders and fuel type used.
11-24-2007, 01:23 PM
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Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (PirateMcFred)
Hey man I am noob to this but you seem to know whats going on so here it goes, I have a 96 lude SRV OBD2, Busted balancer belt got an JDM H22A swapped oil pumps for crank position sensor, everything good there. I have pressure to the fuel rail 34psi, dizzy is fine (spark good) injectors not firing? I have a resistor box on order but not sure if thats the fix? What trips the injectors to fire , I mean how does the ECU know when to send the pulse, Please help!!!
11-25-2007, 06:58 PM
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Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (Gravis20)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Gravis20 »</TD></TR><TR><TD CLASS="quote">Hey man I am noob to this but you seem to know whats going on so here it goes, I have a 96 lude SRV OBD2, Busted balancer belt got an JDM H22A swapped oil pumps for crank position sensor, everything good there. I have pressure to the fuel rail 34psi, dizzy is fine (spark good) injectors not firing? I have a resistor box on order but not sure if thats the fix? What trips the injectors to fire , I mean how does the ECU know when to send the pulse, Please help!!!</TD></TR></TABLE>
you need a resistor box to run OBDI injectors. that is the reason they are not firing. They have no power.
the injectors are signaled by the ecu when to fire. The ecu gets readings from the ECT (engine coolant temperature sensor), IAT (Intake air temperature sensor), TPS (throttle position sensor), MAP (manifold absolute pressure sensor, and primary o2 sensor. given all these inputs to the ecu, the ecu collects the data and determines when to open the injector and how long to keep it open.
Please buy a helms if you plan on working on your car:
http://www.helminc.com
if you have anymore problems, use the search. if you cannot find what you are looking for in the search after usng the recent threads and archived threads, then you may make a thread. Please do not continue to post about your problem in this thread.
thanks.
you need a resistor box to run OBDI injectors. that is the reason they are not firing. They have no power.
the injectors are signaled by the ecu when to fire. The ecu gets readings from the ECT (engine coolant temperature sensor), IAT (Intake air temperature sensor), TPS (throttle position sensor), MAP (manifold absolute pressure sensor, and primary o2 sensor. given all these inputs to the ecu, the ecu collects the data and determines when to open the injector and how long to keep it open.
Please buy a helms if you plan on working on your car:
http://www.helminc.com
if you have anymore problems, use the search. if you cannot find what you are looking for in the search after usng the recent threads and archived threads, then you may make a thread. Please do not continue to post about your problem in this thread.
thanks.
11-25-2007, 07:01 PM
#25
Re: Fuel injectors, duty cycle and how not to look like an idiot. **please read** (98vtec)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 98vtec »</TD></TR><TR><TD CLASS="quote">
you need a resistor box to run OBDI injectors. that is the reason they are not firing. They have no power.
</TD></TR></TABLE>
To nitpick:
96 ludes come with resistor boxes. That's wrong anyways, they'd still be getting power, just too much current, the injector drivers on the ecu would fry.
you need a resistor box to run OBDI injectors. that is the reason they are not firing. They have no power.
</TD></TR></TABLE>
To nitpick:
96 ludes come with resistor boxes. That's wrong anyways, they'd still be getting power, just too much current, the injector drivers on the ecu would fry.
