what do 880cc injectors max out at??
Dec 1, 2009, 06:53 PM
#17
Here's the math for you, just in case you don't what I am referring to:
880cc/min injectors
4 injectors = 3520 cc/min fuel
specific gravity of gasoline (.73-.76, .74 commonly used)
3520*.74=2605 g/min fuel
2605g/min fuel / 454 = 5.73 lb/min fuel
So, what AFR are you going to run? 11:1? 11.5:1?
At 11:1:
5.73lb/min fuel * 11 = 63 lb/min airflow
FP states the Red is a 60 lb/min compressor. So, yes, 880cc injectors should be able to support a maxed out red on pump gas, assuming that your fuel pump is up to task and the injectors truly flow 880cc/min. But as you can see, it will be close. However, you probably won't be able to max out the red on pump gas anyway. So, you should be OK.
My opinion...get a fuel setup that can handle a maxed out Red on E85. Proper injectors and fuel pump (dual pumps). That way you only have to go through it once and be done with it.
880cc/min injectors
4 injectors = 3520 cc/min fuel
specific gravity of gasoline (.73-.76, .74 commonly used)
3520*.74=2605 g/min fuel
2605g/min fuel / 454 = 5.73 lb/min fuel
So, what AFR are you going to run? 11:1? 11.5:1?
At 11:1:
5.73lb/min fuel * 11 = 63 lb/min airflow
FP states the Red is a 60 lb/min compressor. So, yes, 880cc injectors should be able to support a maxed out red on pump gas, assuming that your fuel pump is up to task and the injectors truly flow 880cc/min. But as you can see, it will be close. However, you probably won't be able to max out the red on pump gas anyway. So, you should be OK.
My opinion...get a fuel setup that can handle a maxed out Red on E85. Proper injectors and fuel pump (dual pumps). That way you only have to go through it once and be done with it.
when is a dual fuel pump needed?
Dec 1, 2009, 07:13 PM
#18
Well, it's similar calculations, except that boost now does matter. This is because a fuel pump's flow is inversely proportional with the fuel pressure.
So, to calculate when you need dual pumps, you need to know (1)what boost you will be running and (2)what mass of fuel your pump can supply at that fuel pressure (boost pressure plus 43.5, which is normal base pressure) and (3) your intended AFR.
Let's assume 30 psi held to redline to achieve max airflow:
AMS' test shows a Walbro 255 at 73.5 fuel pressure flows about 220 L/Hr at 14V (at 25psi, about 230L/hr) In reality, you're not going to see 14V at the pump under boost, but let's just go with the numbers for now:
220L/hr = 220000cc/hr = 3667 cc/min
3667* .74 (specific gravity of pump gas) = 2714 g/hr of fuel
2714/454 = 5.98lb/min fuel
So, let's assume 11:1 AFR again:
5.98 * 11 = 65.78 lb/min of airflow
So, in a perfect world, a single Walbro should be able to support a maxed out Red on pump gas. If going to E85, dual pumps are needed.
However, keep in mind, this was assuming that 14V was seen at the pump. If 12V is seen at the pump, the flow might drop 20% (just guessing...but the data is out there). But at least, you can see how to figure things out based on your numbers.
So, to calculate when you need dual pumps, you need to know (1)what boost you will be running and (2)what mass of fuel your pump can supply at that fuel pressure (boost pressure plus 43.5, which is normal base pressure) and (3) your intended AFR.
Let's assume 30 psi held to redline to achieve max airflow:
AMS' test shows a Walbro 255 at 73.5 fuel pressure flows about 220 L/Hr at 14V (at 25psi, about 230L/hr) In reality, you're not going to see 14V at the pump under boost, but let's just go with the numbers for now:
220L/hr = 220000cc/hr = 3667 cc/min
3667* .74 (specific gravity of pump gas) = 2714 g/hr of fuel
2714/454 = 5.98lb/min fuel
So, let's assume 11:1 AFR again:
5.98 * 11 = 65.78 lb/min of airflow
So, in a perfect world, a single Walbro should be able to support a maxed out Red on pump gas. If going to E85, dual pumps are needed.
However, keep in mind, this was assuming that 14V was seen at the pump. If 12V is seen at the pump, the flow might drop 20% (just guessing...but the data is out there). But at least, you can see how to figure things out based on your numbers.
Dec 6, 2009, 04:18 PM
#21
On race gas my 880s and single walbro were able to run a 125mph trap which would be high 400whp range.
Dec 6, 2009, 04:32 PM
#22
the way i was always told if you want 500whp you need a double pumper as gas is needed. yes i know there are some freak evos hitting 500 on single+ meth. but just so you dont have to redo things and get tune to get numbers less then expected i would do 1000cc injectors and bruschur double pumper then you will not have to worry about ****. must easier that way then no worries the job will get done and you will have plenty of room to get more power if you ever wanted to or if you decied to swap to 35r setup or a fp black on higher boost.
Dec 6, 2009, 04:52 PM
#23
Actually if you decide to buy new injectors don't waste your time with small ones. Just get at least bluemax 1650cc or even the 1850cc injectors if you can swing the few hundred extra, it will save you if you ever decide to go bigger/e85 in the future. Right now on E85 I am maxed out with two pumps and 1150cc injectors at around 550whp. I need to put my pumps in parallel instead of series and need bigger injectors. I will just get the 1850s with the tune box ($650) next time and quite wasting my money. I have now gone from 660s to 880s to 1150s and now will need 1850s when I rebuild my engine/turbo, $ I could have saved... oh well.
Dec 6, 2009, 05:55 PM
#25
I know, but who's to say he won't upgrade in the future. If he plans on keeping the car for awhile, it will only be a matter of time 
Really the only reason to buy smaller injectors is
A) you can't get bigger ones to idle properly (bluemax with the box should be fine)
B) you don't want to spend the extra few hundred dollars (650 instead of 400)
Other than that, there is no reason to go with smaller injectors. You can make 300whp on 1850cc injectors at 30%duty cycle, who cares, you have a lot of room to grow then. If bluemax was out when I bought my 1150s I would have those instead right now.
Really the only reason to buy smaller injectors is
A) you can't get bigger ones to idle properly (bluemax with the box should be fine)
B) you don't want to spend the extra few hundred dollars (650 instead of 400)
Other than that, there is no reason to go with smaller injectors. You can make 300whp on 1850cc injectors at 30%duty cycle, who cares, you have a lot of room to grow then. If bluemax was out when I bought my 1150s I would have those instead right now.
Last edited by fre; Dec 6, 2009 at 06:09 PM.
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