02sierraz71_5.3
07-29-2005, 02:35 PM
Ive gotten several emails about this here is my conclusion.
The problem Ive been trying to figure out is what the 8.1L truck injectors flow at 400 kpa since they are rated at 300 kpa. My math said 41 with everything being static and in a perfect world. Just got off the phone after 40 minutes talking with Chuck at delphi. The information I gathered is that injectors are actually rated at around 80% of there max flow to provide some leway. At 400 kpa they guestimated would be flowing around 36 to 38 lbs/hr because of several principales and things I didnt completely understand. I have mine tuned at 34 lbs/hr and am seeing 17.5 ms at 6000 rpms around 100 duty cycle. Problems we run into is a law of diminshing returns where the orifice of the injector is only so big and can only flow so much regardless of how much pressure is behind it and of course with increased pressure and more duty cycle comes heat and detonation can be caused by fuel being too hot. (I think this is why I tend to see detonation at the top of second beginning of third after being wot through first and second). Another problem with overdriving injectors is also the drivers in the pcm being overtaxed.
In my humble opinion these 8.1L truck injectors are not a good upgrade especially if you are forced induction they are designed to flow at 300 kpa not 400 which our rails operate at. Im gonna try and tune around it with raising the ifr value and adjusting through the maf but I doubt I will get below 17 ms or 100% duty cycle. Optimally you want to be around 80% or 14ms wot
Chuck directed me to page 25 of thier catalog he said I should be able to use any of thier high impedance performance injectors there are about 10 of them.
The problem Ive been trying to figure out is what the 8.1L truck injectors flow at 400 kpa since they are rated at 300 kpa. My math said 41 with everything being static and in a perfect world. Just got off the phone after 40 minutes talking with Chuck at delphi. The information I gathered is that injectors are actually rated at around 80% of there max flow to provide some leway. At 400 kpa they guestimated would be flowing around 36 to 38 lbs/hr because of several principales and things I didnt completely understand. I have mine tuned at 34 lbs/hr and am seeing 17.5 ms at 6000 rpms around 100 duty cycle. Problems we run into is a law of diminshing returns where the orifice of the injector is only so big and can only flow so much regardless of how much pressure is behind it and of course with increased pressure and more duty cycle comes heat and detonation can be caused by fuel being too hot. (I think this is why I tend to see detonation at the top of second beginning of third after being wot through first and second). Another problem with overdriving injectors is also the drivers in the pcm being overtaxed.
In my humble opinion these 8.1L truck injectors are not a good upgrade especially if you are forced induction they are designed to flow at 300 kpa not 400 which our rails operate at. Im gonna try and tune around it with raising the ifr value and adjusting through the maf but I doubt I will get below 17 ms or 100% duty cycle. Optimally you want to be around 80% or 14ms wot
Chuck directed me to page 25 of thier catalog he said I should be able to use any of thier high impedance performance injectors there are about 10 of them.