Fuel Injector basics / discussion inside.

[mr. anderson]

Some discussion came up in another thread that went away, I think it's good info so I made a new post.

Here's a little info for you fellas that are going to increase the size of you fuel injector and would like a little info.

There are two basic measurements that have to be taken into account, since were talking american muscle I will go with Standard for the measurements. first measurement, pressure or PSI. this is the line pressure on your fuel system. all vehicles generally run a different pressure our trucks happen to be 58 PSI +/- 2PSI nominal.

fuel injectors as a general rule of thumb are rated at 43.5 PSI

the second measurement is flow rate or pounds per hour (lb/hr) rate generally if there isn't a pressure associated with the flow rate the injector was rated at 43.5 PSI.

this is where it can confuse some. since our fuel system doesn't use 43.5 PSI it changes the flow rate of the injector. the flow rate is directly proportional the increase or decrease in line pressure(PSI), since ours is rated at 58 PSI we essentially increase our flow rate of the originally rated injector at 43.5 PSI.

here is an example. lets say you have a 60 lb/hr injector, this being bought from a mass vendor like summit or jegs, whatever. that 60 lb/hr was rated at 43.5 PSI. now since we are putting that injector into our trucks with the increased fuel pressure from standard it is equivelant to 69.2 lb hr injectors @58 PSI.

you can also do the conversion with any simple conversion search on 'fuel flow conversion calculator'
here's one, any will work to get you into the ball park, scroll down to fuel flow calculator:
http://www.deatschwerks.com/catalog/fuel_calculators.php

The key thing is to check both rates when buying injectors, both flow rate and what the flow rate is referenced at, 43.5 or different. ie this injector is rated at 69 lb/hr @ 58PSI

there is also injector impedence. I will discuss that at a later time just know for now there is high and low impedence injectors, there is a difference. both have their positive and negatives. and definately have their applications dependent on what they're gonna be used for.

duty cycle is also important, as a rule of thumb you do not want to exceed 80% duty cycle of the injector, this gives fudge factor for the different temps, and baro pressures.

hope this helps.

anything else, ya'll are free to comment and share the wealth of knowledge. I know there are others that have learned the pain of the fuel system with the increase in power.

 

[rottenronnie]

Thanks for the info Mr. Anderson.

Because they are a mass produced item, I also had mine flowed.

The "richest" one I stuck in the dreaded #3 hole as I was told long ago this is the hole that can go lean in these engines.
The rest of the richest ones went in the front. All the little things add up after a while.

It is just another way to tune...

Ronnie

 

[mr. anderson]

great idea! were the flow rates that far off? or were they all within reasonable tolerances?

 

[rottenronnie]

great idea! were the flow rates that far off? or were they all within reasonable tolerances?

I think they were all within 10% of each other. I will look and see if I can find the actual numbers as I could be wrong they may have been closer, I forget.

 

[TurboFreak]

I always buy sets that are flow balanced. The ones on my Silverado were within 1% of each other and I put the highest flowing in the #7 cylinder as that one seems to run the leanest. Mine were 63.4 lbs/hr @ 3 BAR(43.5 PSI). Many manufacturers also use cc/min for flow rates and you can convert to lbs/hr by dividing by 10.5.

Here is the formula I used to convert to a different fuel pressure:

√(a/b)*c = d (where a = new fuel pressure, b = old fuel pressure, c = the old fuel rating and d = the new flow rating)

√ = square root
/ = divide
* = multiply

So, you take the new fuel pressure (a) you want and divide by the old fuel pressure (b), then you take the square root of that and multiply it by the old rating (c) to get your new rating (d).

Ex:

√(58/43.5)*63.4 = 73.2

 

[Stanimal]

another thing to remember, 60lb (also known as 600cc i believe) injectors are good to 600 hp total. so if you have a 6 cylender engine with 6 60lb injectors the engine is good for 600 hp, same with 10 of them in a 10 cylender. 50lb are good to 500 hp. these figures take into consideration a 75% duty cycle at 600 hp for a 60lb injector. this is why srt's are so limited with stock injectors, their injectors are at 80% duty or higher from the factory, not much room to safely play. one of my first mods was a set of 80lb injectors.

 

[Ram From Hell]

I think they were all within 10% of each other. I will look and see if I can find the actual numbers as I could be wrong they may have been closer, I forget.

Yeah. 10% would be a significant margin of difference.

I think between 1%-0.5% is where you want to be.

 

[rottenronnie]

Yeah. 10% would be a significant margin of difference.

Found it- Anywhere from a high of nearly 395 cc/min. to a low of 338 cc/min (a whopping 17% from leanest to richest).
I moved the richer ones from the back to the front.
It is the first set I've had flowed on a 2005. Is that about normal or are buddies numbers whacked??
They seem to be fine for the power numbers I have.
The A/F is stable and safe during a heavy dyno pull.

 

[Ram From Hell]

Found it- Anywhere from a high of nearly 395 cc/min. to a low of 338 cc/min (a whopping 17% from leanest to richest).
I moved the richer ones from the back to the front.
It is the first set I've had flowed on a 2005. Is that about normal or are buddies numbers whacked??
They seem to be fine for the power numbers I have.
The A/F is stable and safe during a heavy dyno pull.

Big difference between having your injectors "flowed" and "flow-matched". While it's good to know what your injectors are flowing, it's not particularly helpful if those numbers are quite a ways off. If you can tune on a per-cylinder basis, not too big of a deal. If you're tuning bank-to-bank with a pair of O2's, you'll have less than optimal results.

Those numbers seem to be pretty darned far apart, IMHO.

 

[rottenronnie]

Big difference between having your injectors "flowed" and "flow-matched". While it's good to know what your injectors are flowing, it's not particularly helpful if those numbers are quite a ways off. If you can tune on a per-cylinder basis, not too big of a deal. If you're tuning bank-to-bank with a pair of O2's, you'll have less than optimal results.

Those numbers seem to be pretty darned far apart, IMHO.

It might be best to have them checked elsewhere or just buy a set of 10 that are matched. Plug readings are all very close to the same as far as coloring goes; but, like you mention, the O2 sensors are only going to see the combined result. Thanks for the input.

 

[71dusterjon]

just curious, i remember talking to several guys on here about how paxton uses two fuel pumps to supply more pressure vs changing injectors. i believe i still have the stock injectors so if i were to have dc performance step up only my injectors without changing my fuel pumps and retune my engine, will this be a big difference in power due to my injectors would flow more?

 

[TurboFreak]

another thing to remember, 60lb (also known as 600cc i believe) injectors are good to 600 hp total. so if you have a 6 cylender engine with 6 60lb injectors the engine is good for 600 hp, same with 10 of them in a 10 cylender. 50lb are good to 500 hp. these figures take into consideration a 75% duty cycle at 600 hp for a 60lb injector. this is why srt's are so limited with stock injectors, their injectors are at 80% duty or higher from the factory, not much room to safely play. one of my first mods was a set of 80lb injectors.

Not correct. Let's say a 4 cylinder car has 60lb injectors then they would be good for about 450 crank hp assuming 80% Injector Duty Cycle(IDC), 58 PSI and a .50 Brake Specific Fuel Consumption(BSFC). If you install those same(same flow but 8 of them) injectors in a 8 cylinder car they would be good for 900 crank hp.

60 lb/hr injector Ex:

Cylinders = 4
BSFC = 0.50
IDC = 0.80
Fuel Pressure = 58
Crank HP = 450

Cylinders = 6
BSFC = 0.50
IDC = 0.80
Fuel Pressure = 58
Crank HP = 670

Cylinders = 8
BSFC = 0.50
IDC = 0.80
Fuel Pressure = 58
Crank HP = 900

Cylinders = 10
BSFC = 0.50
IDC = 0.80
Fuel Pressure = 58
Crank HP = 1125

The more injectors you have the higher the potential hp.

BTW, injectors do not make power they just support it. Putting larger ones will not make more hp but you will have the ability to make more with a power adder.

I put 60 lb/hr(43.5 PSI/3 bar) or 70 lb/hr(58 PSI/4 bar) in my Silverado because I am going to turbocharge it later. I am making the same HP that I was with the stock 25 lb/hr(58 PSI) but my IDC is down to 35%. These injectors have the ability to support more HP.

 

[TNVIPER]

if you dont change the tune will putting the bigger injectors in result in drivability problems (normal driving, not WOT)?...I understand the engine needs to be re-tuned for optimum WOT performance but will the PCM adapt for normal driving until a tune can be done?

 

[mr. anderson]

TNviper, the quick answer is yes drivability problems, and NO, you shouldn't do it without a tune especially if the injector are a large jump in size. because the stock tune or what ever the current tune is for whatever size injectors you have in there now, the computer only knows that size injector and inputs fuel based on size injectors fuel curve or fuel map, on that reference, and with speed density(our trucks), vice a MAF sensor, even less can be adjusted for via the computer.

and 71 duster john, yes you could do that, but if you did go with larger injectors why not just get a programmer, 2 bar map also and nix the extra fuel pumps. I would go one or the other. with the added fuel pumps along with the injectors that would be A LOT of fuel. not really needed, go with one system or the other but both are not needed below a certain HP level, once you build your engine and are pushing HP at the 1K RWHP level then yes, I would have a go with twin 255 fuel pumps, but then your changing the whole fuel system out. lines and rails included.

 

[71dusterjon]

never knew that. thanks for the info.

 

[TurboFreak]

if you dont change the tune will putting the bigger injectors in result in drivability problems (normal driving, not WOT)?...I understand the engine needs to be re-tuned for optimum WOT performance but will the PCM adapt for normal driving until a tune can be done?

The PCM has a +/- 33% adjustment in closed loop but if you go bigger than that it will run pig rich. Regardless you should re-tune otherwise your open loop will be way off.

 

[JTS VENOM PERFORMANCE]

another thing to remember, 60lb (also known as 600cc i believe) injectors are good to 600 hp total. so if you have a 6 cylender engine with 6 60lb injectors the engine is good for 600 hp, same with 10 of them in a 10 cylender. 50lb are good to 500 hp. these figures take into consideration a 75% duty cycle at 600 hp for a 60lb injector. this is why srt's are so limited with stock injectors, their injectors are at 80% duty or higher from the factory, not much room to safely play. one of my first mods was a set of 80lb injectors.

I ran 60 lb flowed injectors and made 1030rwhp at 70% duty cycle

 

[mysrt10]

where can i get a set that has been flow matched?