Whats wrong with running 100% duty cycle on injectors
01-18-12, 09:31 PM
#1
imitek
Thread Starter
Whats wrong with running 100% duty cycle on injectors
I always hear people say u should run around 80% and maxin an injector is bad but why
Thanks
Ive done about 15 min of resurch and found no reason so if any 1 could explain why its bad thanks
Thanks
Ive done about 15 min of resurch and found no reason so if any 1 could explain why its bad thanks
01-18-12, 09:40 PM
#2
1.3L piston eater
im no expert but i believe after 80% they start to overheat and you run out of fuel.. plus why would you want to max out your injectors if you get a boost spike your motors done!
01-18-12, 09:53 PM
#3
F-IT
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theres not enough time for them to open and close properly. has nothing to do with heat or starvation. simply the solenoid can't control the valve and it will start to float. never really closing and never really opening.
01-19-12, 12:11 AM
#5
imitek
Thread Starter
But if u max out the injector its just open right so whats the problem it dosent need to control anything just leave it open right via pulse ( dont take it the wrong way im just intrested in info )
Also brings me to another situation if you increase the fuel presure surely that would effect the opening and closing of the injector more load behind the injector pin
01-19-12, 12:24 AM
#6
imitek
Thread Starter
Is the max u want to go
Your answer does not explain it states and the answer above yours explains
You should have explaind why its not efficant and how it wont meter fuel
01-19-12, 12:27 AM
#7
oh it has alot to do with heat and less to do with efficiency as the injector will still peak when it is at 100% duty cycle regardless. try taking an old junk injector and apply 12 volts to it and let it sit for a bit, come back and feel just how warm it got in less than 5 minutes and think about why that is.
the coils will eventually fail if you leave it applied full open, now what happens when the coil fails? injector snaps shut, duty cycle falls to 0, injector output falls to 0, engine output falls to quite a bit below 50%.
the lower the duty cycle the cooler the injectors run, the more they have to work the hotter they get, the hotter they get the quicker they fail.
i have taken injectors to 100%, accidentally, but not metering the fuel properly above 80%? that's a load of **** and an urban myth. the only instance you see a real difference is once you lose duty completely.
the coils will eventually fail if you leave it applied full open, now what happens when the coil fails? injector snaps shut, duty cycle falls to 0, injector output falls to 0, engine output falls to quite a bit below 50%.
the lower the duty cycle the cooler the injectors run, the more they have to work the hotter they get, the hotter they get the quicker they fail.
i have taken injectors to 100%, accidentally, but not metering the fuel properly above 80%? that's a load of **** and an urban myth. the only instance you see a real difference is once you lose duty completely.
Last edited by RotaryEvolution; 01-19-12 at 12:37 AM.
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01-19-12, 12:29 AM
#8
F-IT
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you could have the potential for burning up the windings inside the coil of the injector. they are designed to be help open for long lengths of time.
http://docinjector.com/info1.htm
http://docinjector.com/info1.htm
01-19-12, 12:31 AM
#9
imitek
Thread Starter
Thanks for our input i thort it mabe somthing to do with heat as well then i read fuel passing threw injector has a cooling effect
01-19-12, 12:37 AM
#10
imitek
Thread Starter
oh it has alot to do with heat and less to do with efficiency as the injector will still peak when it is at 100% duty cycle regardless. try taking an old junk injector and apply 12 volts to it and let it sit for a bit, come back and feel just how warm it got in less than 5 minutes and think about why that is.
the coils will eventually fail if you leave it applied full open, now what happens when the coil fails? injector snaps shut, duty cycle falls to 0, injector output falls to 0, engine output falls to quite a bit below 50%.
the lower the duty cycle the cooler the injectors run, the more they have to work the hotter they get, the hotter they get the quicker they fail.
the coils will eventually fail if you leave it applied full open, now what happens when the coil fails? injector snaps shut, duty cycle falls to 0, injector output falls to 0, engine output falls to quite a bit below 50%.
the lower the duty cycle the cooler the injectors run, the more they have to work the hotter they get, the hotter they get the quicker they fail.
I no it states 100% duty but thats the injector not the input signal right?
01-19-12, 12:47 AM
#12
100% duty cycle is 100% open 100% of the time.
in reality i don't see a huge harm in running to 95% DC for short periods of time. how many people do 200mph passes for 5 minutes straight? no one.
the only downside to this is you have no room for more boost, a spike of a few psi will cost you a motor.
in reality i don't see a huge harm in running to 95% DC for short periods of time. how many people do 200mph passes for 5 minutes straight? no one.
the only downside to this is you have no room for more boost, a spike of a few psi will cost you a motor.
Last edited by RotaryEvolution; 01-19-12 at 12:50 AM.
01-19-12, 01:05 AM
#13
imitek
Thread Starter
I always thaught because of the reactance time ( injecter dead time ) you have a window to pulse
Ok thanks guys thanks for the explanations you have helped lots
Ok thanks guys thanks for the explanations you have helped lots
01-19-12, 04:23 AM
#14
Arrogant Wankeler
What's with the "boost cut will kill your motor" crap, that is what overboost fuel or ignition cuts are for, you can never rule out a gate diaphragm failing or a line coming off.
01-19-12, 06:35 AM
#15
gif from wikipedia
this is what the signal controlling your injectors looks like. 100% duty is constant ~12V. nothing wrong with 100% duty, but you effectively lose control of your injector.
in normal engine operation, you cannot really accurately control how much air your engine is consuming, but you can meter the fuel very precisely. but at 100% d/c, any increase in air will lead to lean condition. im not sure if it would overheat the injector at 100%, but as karack mentioned, it would be very easy to test on a bench with a 12V supply..
this is what the signal controlling your injectors looks like. 100% duty is constant ~12V. nothing wrong with 100% duty, but you effectively lose control of your injector.
in normal engine operation, you cannot really accurately control how much air your engine is consuming, but you can meter the fuel very precisely. but at 100% d/c, any increase in air will lead to lean condition. im not sure if it would overheat the injector at 100%, but as karack mentioned, it would be very easy to test on a bench with a 12V supply..
01-19-12, 09:57 AM
#16
4th string e-armchair QB
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oh it has alot to do with heat and less to do with efficiency as the injector will still peak when it is at 100% duty cycle regardless. try taking an old junk injector and apply 12 volts to it and let it sit for a bit, come back and feel just how warm it got in less than 5 minutes and think about why that is.
the coils will eventually fail if you leave it applied full open, now what happens when the coil fails? injector snaps shut, duty cycle falls to 0, injector output falls to 0, engine output falls to quite a bit below 50%.
the lower the duty cycle the cooler the injectors run, the more they have to work the hotter they get, the hotter they get the quicker they fail.
i have taken injectors to 100%, accidentally, but not metering the fuel properly above 80%? that's a load of **** and an urban myth. the only instance you see a real difference is once you lose duty completely.
the coils will eventually fail if you leave it applied full open, now what happens when the coil fails? injector snaps shut, duty cycle falls to 0, injector output falls to 0, engine output falls to quite a bit below 50%.
the lower the duty cycle the cooler the injectors run, the more they have to work the hotter they get, the hotter they get the quicker they fail.
i have taken injectors to 100%, accidentally, but not metering the fuel properly above 80%? that's a load of **** and an urban myth. the only instance you see a real difference is once you lose duty completely.
Image courtesy of Paul Yaw, showing measured output of the various coloured-top Bosch 1600cc injectors.
The reason it is not recommended running above 80% DC on these specific injectors is clearly shown in the graph. Whereas between 65% and 70% DC, the metered increase in fuel is fairly predictable and linear to the pulsewidth increase, in between 80% and 85%, it is not so much. Now, in practicality when you are tuning on the dyno, and shooting for an AFR, then whatever DC you end up with is pretty irrelevant, but the real issue comes at a later time when your compensation maps start altering the pulsewidth on the injector based on inputs. When it adds 1 or 2% to DC, the ECU expects a 1 or 2% increase in fuel flow (as would happen in the lower DC ranges). Once you get above 80%, the ECU may not get the increase it expected, or may get much more than expected.
01-19-12, 10:53 AM
#17
By efficiency most people are actually referring to linearity. And I guess you would say that these injectors are accurately metering fuel in a linear fashion between 80 and 95% DC?
Image courtesy of Paul Yaw, showing measured output of the various coloured-top Bosch 1600cc injectors.
The reason it is not recommended running above 80% DC on these specific injectors is clearly shown in the graph. Whereas between 65% and 70% DC, the metered increase in fuel is fairly predictable and linear to the pulsewidth increase, in between 80% and 85%, it is not so much. Now, in practicality when you are tuning on the dyno, and shooting for an AFR, then whatever DC you end up with is pretty irrelevant, but the real issue comes at a later time when your compensation maps start altering the pulsewidth on the injector based on inputs. When it adds 1 or 2% to DC, the ECU expects a 1 or 2% increase in fuel flow (as would happen in the lower DC ranges). Once you get above 80%, the ECU may not get the increase it expected, or may get much more than expected.
Image courtesy of Paul Yaw, showing measured output of the various coloured-top Bosch 1600cc injectors.
The reason it is not recommended running above 80% DC on these specific injectors is clearly shown in the graph. Whereas between 65% and 70% DC, the metered increase in fuel is fairly predictable and linear to the pulsewidth increase, in between 80% and 85%, it is not so much. Now, in practicality when you are tuning on the dyno, and shooting for an AFR, then whatever DC you end up with is pretty irrelevant, but the real issue comes at a later time when your compensation maps start altering the pulsewidth on the injector based on inputs. When it adds 1 or 2% to DC, the ECU expects a 1 or 2% increase in fuel flow (as would happen in the lower DC ranges). Once you get above 80%, the ECU may not get the increase it expected, or may get much more than expected.
i'm not saying this is a great idea but if you build the engine and tune it properly that goes a long ways towards it not being such a huge deal.
Last edited by RotaryEvolution; 01-19-12 at 10:56 AM.
01-19-12, 11:52 AM
#18
imitek
Thread Starter
gif from wikipedia
this is what the signal controlling your injectors looks like. 100% duty is constant ~12V. nothing wrong with 100% duty, but you effectively lose control of your injector.
in normal engine operation, you cannot really accurately control how much air your engine is consuming, but you can meter the fuel very precisely. but at 100% d/c, any increase in air will lead to lean condition. im not sure if it would overheat the injector at 100%, but as karack mentioned, it would be very easy to test on a bench with a 12V supply..
this is what the signal controlling your injectors looks like. 100% duty is constant ~12V. nothing wrong with 100% duty, but you effectively lose control of your injector.
in normal engine operation, you cannot really accurately control how much air your engine is consuming, but you can meter the fuel very precisely. but at 100% d/c, any increase in air will lead to lean condition. im not sure if it would overheat the injector at 100%, but as karack mentioned, it would be very easy to test on a bench with a 12V supply..
Right so if u max out the injectors and u go into a diffrent density area ( diffrent humidity) your ecu cant control any more fuel comming in because its maxed out ok makes perfict sence
If some 1 just said that at the begining
01-19-12, 12:01 PM
#20
imitek
Thread Starter
By efficiency most people are actually referring to linearity. And I guess you would say that these injectors are accurately metering fuel in a linear fashion between 80 and 95% DC?
Image courtesy of Paul Yaw, showing measured output of the various coloured-top Bosch 1600cc injectors.
The reason it is not recommended running above 80% DC on these specific injectors is clearly shown in the graph. Whereas between 65% and 70% DC, the metered increase in fuel is fairly predictable and linear to the pulsewidth increase, in between 80% and 85%, it is not so much. Now, in practicality when you are tuning on the dyno, and shooting for an AFR, then whatever DC you end up with is pretty irrelevant, but the real issue comes at a later time when your compensation maps start altering the pulsewidth on the injector based on inputs. When it adds 1 or 2% to DC, the ECU expects a 1 or 2% increase in fuel flow (as would happen in the lower DC ranges). Once you get above 80%, the ECU may not get the increase it expected, or may get much more than expected.
Image courtesy of Paul Yaw, showing measured output of the various coloured-top Bosch 1600cc injectors.
The reason it is not recommended running above 80% DC on these specific injectors is clearly shown in the graph. Whereas between 65% and 70% DC, the metered increase in fuel is fairly predictable and linear to the pulsewidth increase, in between 80% and 85%, it is not so much. Now, in practicality when you are tuning on the dyno, and shooting for an AFR, then whatever DC you end up with is pretty irrelevant, but the real issue comes at a later time when your compensation maps start altering the pulsewidth on the injector based on inputs. When it adds 1 or 2% to DC, the ECU expects a 1 or 2% increase in fuel flow (as would happen in the lower DC ranges). Once you get above 80%, the ECU may not get the increase it expected, or may get much more than expected.
01-19-12, 12:21 PM
#22
That chart is a representation of fuel flow at different duty cycles. As you can see from 20% to 85% the flow is fairly linear and predictable. After 85% the flow becomes non linear IE- if you are at 85% duty cycle and request an extra 10% duty cycle you may get a unpredictable and non linear increase in flow. Lets say from 40% to 50% you get an increase of about 200cc min but an increase from 85% to 95% and you get an increase of roughly 300cc min.
01-19-12, 01:22 PM
#23
the output also seems to flatline from 85-93% not increasing fuel flow and then gets a massive boost as soon as the cycle reaches 93% open, flowing the maximum that the injector can flow. the green line actually shows that one injector pushing 1800ccs max, while during regular operation is no higher than any others in the set of 4. showing that the injectors actually hit 100% duty cycle at about 93% in reality, or his test machine is fubar, the same graph shows 0% output below 10% duty cycle so i'm not sure what to believe, or his scaling is inaccurate. if the scaling is inaccuarate then so is the point in differences at 85%.
worst case is there is a slight lean dip for 4% duty cycle just before 100% duty cycle(still leaving you up to 96% duty cycle before possibly getting a slight dip in AFRs), next worst case the injectors vary by a whole 6% output(100cc/min variance at 1500). again, not anything to be super super concerned about. 10% or higher is where the orange/red flag starts to pop up. for peak power sake though, 0% variance is ideal but you will almost never get near ideal unless you move to newer injector technology.
worst case is there is a slight lean dip for 4% duty cycle just before 100% duty cycle(still leaving you up to 96% duty cycle before possibly getting a slight dip in AFRs), next worst case the injectors vary by a whole 6% output(100cc/min variance at 1500). again, not anything to be super super concerned about. 10% or higher is where the orange/red flag starts to pop up. for peak power sake though, 0% variance is ideal but you will almost never get near ideal unless you move to newer injector technology.
Last edited by RotaryEvolution; 01-19-12 at 01:39 PM.
01-21-12, 09:54 AM
#24
Lives on the Forum
A simple explanation of injector duty cycle with a calculator to help: http://injector-rehab.com/shop/idc.html
Not sure why one would be taking the time to trying to figure out why they "can't" run 100% duty cycle rather than spending the time to figure out how to get enough fuel available to NOT be running at 100%...
Not sure why one would be taking the time to trying to figure out why they "can't" run 100% duty cycle rather than spending the time to figure out how to get enough fuel available to NOT be running at 100%...
01-21-12, 01:15 PM
#25
T67, did I say 7?
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