Some more injector info...
In my testing these injectors, I found that maxing out the stock fuel injectors was going to be fairly easy. Here at sea level, at 17psi and on a completely factory Cruze aside from tuning, the factory fuel injectors were running at 19-20ms pulse widths. Once swapped to the 50# injectors, the pulse widths dropped to 12.4 at a max at the same 17psi, and ended up in the low 13 range at the end of tuning.
You'll often read or hear about injector duty cycle if you research fuel injectors, and how you don't want to go over 80% or 85% or 90% etc, whatever figure the author may choose. A better way to understand this is through the pulse widths, which is the physical time that an injector is activated to spray, measured in milliseconds...
When you max out the fuel injectors, what you're doing is reaching the physical time limitation that the injector has to spray fuel. This time window shrinks as the engine speed increases. To give this an example, at 3000rpm, it takes 40 milliseconds for the crankshaft to complete 2 revolutions, or to complete its entire 4 stroke cycle. At 6000rpm, it take 20 milliseconds. This 20 milliseconds at 6000rpm represents the maximum amount of time that a fuel injector would have to introduce fuel into the incoming air stream for that cycle.
Now if you compare that to the fuel injector pulse widths I mention above, at 19-20ms, the factory injectors were reaching their maximum by a full throttle shift point of 6300rpm. This means that even if the computer needed to command more fuel into the motor, there wouldn't be the ability to injector more fuel. An example of that need would be if I were to have commanded more boost. Once this maximum time limit is reached, the air/fuel ratio will increasingly lean out from that engine rpm and up, getting leaner as rpms increase.
This should help underscore the importance of knowing when to upgrade your fuel injectors. Again these test figures were at sea level air density, at 17psi on a stock Cruze, and on an Overkill tune that aims for a safe and proper 11.0-11.2:1 air/fuel ratio. Boost pressure, altitude to some extent, and air/fuel ratio will all play a factory in injector pulse widths. No matter if you're providing scans to your tuner (including me) through HPTuners, Diablosport or EFI Live, you have the ability to look at your own scans, take note of your injector pulse widths, and see whether you should be thinking about an injector upgrade.
Maximum injector pulse widths can be found by taking 120,000 divided by engine rpm. Here's examples of maximum injector pulse widths in ms, compared to engine rpm:
22ipw = 5450rpm
21ipw = 5700rpm
20ipw = 6000rpm
19ipw = 6300rpm
And if you want to calculate what injector duty cycle is, you take engine rpms x injector ipw, then divide that by 1200. For example, (6000rpms x 20ipw) / 1200 = 100% duty cycle.
In my testing these injectors, I found that maxing out the stock fuel injectors was going to be fairly easy. Here at sea level, at 17psi and on a completely factory Cruze aside from tuning, the factory fuel injectors were running at 19-20ms pulse widths. Once swapped to the 50# injectors, the pulse widths dropped to 12.4 at a max at the same 17psi, and ended up in the low 13 range at the end of tuning.
You'll often read or hear about injector duty cycle if you research fuel injectors, and how you don't want to go over 80% or 85% or 90% etc, whatever figure the author may choose. A better way to understand this is through the pulse widths, which is the physical time that an injector is activated to spray, measured in milliseconds...
When you max out the fuel injectors, what you're doing is reaching the physical time limitation that the injector has to spray fuel. This time window shrinks as the engine speed increases. To give this an example, at 3000rpm, it takes 40 milliseconds for the crankshaft to complete 2 revolutions, or to complete its entire 4 stroke cycle. At 6000rpm, it take 20 milliseconds. This 20 milliseconds at 6000rpm represents the maximum amount of time that a fuel injector would have to introduce fuel into the incoming air stream for that cycle.
Now if you compare that to the fuel injector pulse widths I mention above, at 19-20ms, the factory injectors were reaching their maximum by a full throttle shift point of 6300rpm. This means that even if the computer needed to command more fuel into the motor, there wouldn't be the ability to injector more fuel. An example of that need would be if I were to have commanded more boost. Once this maximum time limit is reached, the air/fuel ratio will increasingly lean out from that engine rpm and up, getting leaner as rpms increase.
This should help underscore the importance of knowing when to upgrade your fuel injectors. Again these test figures were at sea level air density, at 17psi on a stock Cruze, and on an Overkill tune that aims for a safe and proper 11.0-11.2:1 air/fuel ratio. Boost pressure, altitude to some extent, and air/fuel ratio will all play a factory in injector pulse widths. No matter if you're providing scans to your tuner (including me) through HPTuners, Diablosport or EFI Live, you have the ability to look at your own scans, take note of your injector pulse widths, and see whether you should be thinking about an injector upgrade.
Maximum injector pulse widths can be found by taking 120,000 divided by engine rpm. Here's examples of maximum injector pulse widths in ms, compared to engine rpm:
22ipw = 5450rpm
21ipw = 5700rpm
20ipw = 6000rpm
19ipw = 6300rpm
And if you want to calculate what injector duty cycle is, you take engine rpms x injector ipw, then divide that by 1200. For example, (6000rpms x 20ipw) / 1200 = 100% duty cycle.
