At what point are injectors needed?
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Evolving Member
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At what point are injectors needed?
Simple as that. Say, with all bolt ons but not a turbo upgrade - would you need bigger injectors?
ie: fmic,tbe,intake, o2 , manifold etc.
Essentially maxing out stock IX turbo.
ie: fmic,tbe,intake, o2 , manifold etc.
Essentially maxing out stock IX turbo.
He just said that was with meth. Meth/alky injection makes injectors even LESS necessary, because it burns in the cylinder as fuel, thus causing the tune to remove a lot of fuel from the equation, which lowers the Injector Duty Cycle. Running high power on straight pump gas would increase the need for injectors.
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So is there a general rule or does it vary by the application (cams, octane, tune, etc)? I've got the fuel pump and 264/272 cams in the garage waiting to be installed but I'm wondering if I should order new injectors and new head studs and install it all at once just to be safe. Or is that overkill?
The stock turbo has a hard time outrunning the stock injectors, but it's very close. On race gas with a specific gravity of .724, 43 lbs/min (stock turbo completely maxed out), and a target AFR of 12:1, you are going to get IDCs of 97% mathematically, and this is what I saw on my car. On pump gas however with a SG of about .76 usually, and a target AFR of 11:1, you are looking at 101% IDC. I saw as high as 102%. Since you really can't be over 100%, AFR will vary from target, by a tenth or two in this example.
So the answer is the stock injectors will keep up with the stock turbo, as long as you are not trying to run super rich target AFRs.
The pump on the other hand can only keep up if it is rewired. Most people just go to a bigger pump since they are cheap and easy to do. But for those looking to keep the stock pump I'll run through the numbers on that as well. Race gas and pump gas (and corresponding target AFRs) only change the supported airflow by about 1 lb/min, so it's not worth breaking it out. Non rewired the stock pump will only support 35 lbs/min or so, at 20 psi (where the stock turbo maxes out at max airflow/time with cams and other typical mods), which is not enough. For poeple maxing out the stock turbo, this results in a mathematical actual AFR of about 12.5:1. And this is exactly what I was getting on my wideband, despite a target AFR of 11:1 to 12:1 depending on fuel.
I then got off my lazy *** and did the rewire, which allows the stock pump to support 44-55 lbs/min for pump/race gas, repsectively, mathematically. In reality, wideband AFR was dead on target AFR at 11:1 on pump gas and about 40 lbs/min. On race gas I got up to 43 lbs/min (turbo maxed out) and the wideband showed 12:1, which was dead on with the target AFR of 12:1, all the way to redline.
So the stock pump is big enough, if it is rewired. If you are not running cams and need to run 23-25 psi at redline to get the same 42-43 lbs/min the pump becomes slightly smaller, but its' still capable of keeping up. The injectors are big enough regardless of the conditions.
So the answer is the stock injectors will keep up with the stock turbo, as long as you are not trying to run super rich target AFRs.
The pump on the other hand can only keep up if it is rewired. Most people just go to a bigger pump since they are cheap and easy to do. But for those looking to keep the stock pump I'll run through the numbers on that as well. Race gas and pump gas (and corresponding target AFRs) only change the supported airflow by about 1 lb/min, so it's not worth breaking it out. Non rewired the stock pump will only support 35 lbs/min or so, at 20 psi (where the stock turbo maxes out at max airflow/time with cams and other typical mods), which is not enough. For poeple maxing out the stock turbo, this results in a mathematical actual AFR of about 12.5:1. And this is exactly what I was getting on my wideband, despite a target AFR of 11:1 to 12:1 depending on fuel.
I then got off my lazy *** and did the rewire, which allows the stock pump to support 44-55 lbs/min for pump/race gas, repsectively, mathematically. In reality, wideband AFR was dead on target AFR at 11:1 on pump gas and about 40 lbs/min. On race gas I got up to 43 lbs/min (turbo maxed out) and the wideband showed 12:1, which was dead on with the target AFR of 12:1, all the way to redline.
So the stock pump is big enough, if it is rewired. If you are not running cams and need to run 23-25 psi at redline to get the same 42-43 lbs/min the pump becomes slightly smaller, but its' still capable of keeping up. The injectors are big enough regardless of the conditions.
Originally Posted by kjewer1
The stock turbo has a hard time outrunning the stock injectors, but it's very close. On race gas with a specific gravity of .724, 43 lbs/min (stock turbo completely maxed out), and a target AFR of 12:1, you are going to get IDCs of 97% mathematically, and this is what I saw on my car. On pump gas however with a SG of about .76 usually, and a target AFR of 11:1, you are looking at 101% IDC. I saw as high as 102%. Since you really can't be over 100%, AFR will vary from target, by a tenth or two in this example.
So the answer is the stock injectors will keep up with the stock turbo, as long as you are not trying to run super rich target AFRs.
The pump on the other hand can only keep up if it is rewired. Most people just go to a bigger pump since they are cheap and easy to do. But for those looking to keep the stock pump I'll run through the numbers on that as well. Race gas and pump gas (and corresponding target AFRs) only change the supported airflow by about 1 lb/min, so it's not worth breaking it out. Non rewired the stock pump will only support 35 lbs/min or so, at 20 psi (where the stock turbo maxes out at max airflow/time with cams and other typical mods), which is not enough. For poeple maxing out the stock turbo, this results in a mathematical actual AFR of about 12.5:1. And this is exactly what I was getting on my wideband, despite a target AFR of 11:1 to 12:1 depending on fuel.
I then got off my lazy *** and did the rewire, which allows the stock pump to support 44-55 lbs/min for pump/race gas, repsectively, mathematically. In reality, wideband AFR was dead on target AFR at 11:1 on pump gas and about 40 lbs/min. On race gas I got up to 43 lbs/min (turbo maxed out) and the wideband showed 12:1, which was dead on with the target AFR of 12:1, all the way to redline.
So the stock pump is big enough, if it is rewired. If you are not running cams and need to run 23-25 psi at redline to get the same 42-43 lbs/min the pump becomes slightly smaller, but its' still capable of keeping up. The injectors are big enough regardless of the conditions.
So the answer is the stock injectors will keep up with the stock turbo, as long as you are not trying to run super rich target AFRs.
The pump on the other hand can only keep up if it is rewired. Most people just go to a bigger pump since they are cheap and easy to do. But for those looking to keep the stock pump I'll run through the numbers on that as well. Race gas and pump gas (and corresponding target AFRs) only change the supported airflow by about 1 lb/min, so it's not worth breaking it out. Non rewired the stock pump will only support 35 lbs/min or so, at 20 psi (where the stock turbo maxes out at max airflow/time with cams and other typical mods), which is not enough. For poeple maxing out the stock turbo, this results in a mathematical actual AFR of about 12.5:1. And this is exactly what I was getting on my wideband, despite a target AFR of 11:1 to 12:1 depending on fuel.
I then got off my lazy *** and did the rewire, which allows the stock pump to support 44-55 lbs/min for pump/race gas, repsectively, mathematically. In reality, wideband AFR was dead on target AFR at 11:1 on pump gas and about 40 lbs/min. On race gas I got up to 43 lbs/min (turbo maxed out) and the wideband showed 12:1, which was dead on with the target AFR of 12:1, all the way to redline.
So the stock pump is big enough, if it is rewired. If you are not running cams and need to run 23-25 psi at redline to get the same 42-43 lbs/min the pump becomes slightly smaller, but its' still capable of keeping up. The injectors are big enough regardless of the conditions.
Every car does 
The problem is that it's still a small wire, 18 ga or so. What is typically involved is using the stock wire to trigger a relay that switches an 8 or 10 ga wire that now feeds the pump directly from the battery. If you want to keep the stock dual voltage circuit (no reg for example) you could get slick and trigger the relay with whatever triggers the switchover to the high voltage line. I never looked into what is required to do this, since DSMlink effectively disabled the dual voltage circuit (defaulting to the full vontage), but it should be quite simple for anyone with the FSMs.
The problem is that it's still a small wire, 18 ga or so. What is typically involved is using the stock wire to trigger a relay that switches an 8 or 10 ga wire that now feeds the pump directly from the battery. If you want to keep the stock dual voltage circuit (no reg for example) you could get slick and trigger the relay with whatever triggers the switchover to the high voltage line. I never looked into what is required to do this, since DSMlink effectively disabled the dual voltage circuit (defaulting to the full vontage), but it should be quite simple for anyone with the FSMs.