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post #1 of 22 (permalink) Old 08-20-2019 Thread Starter
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injector upgrade question

I seem to be running into some contradicting information about the necessity of increasing the stock 19lb. injectors.
At the moment, I am trying to put together a budget if I move forward with a cam swap.
I am leaning towards needing to upgrade to 24lb injectors, and will also get expert opinions once I settle on a shop, but for now I wanted to get some feedback from anyone out there who has experience in this area.


Currently I just have the typical CAI, T/B, Plenum, O/R-H, and Bama 93 tune, and the car runs absolutely fine with the stockers.
I am thinking about swapping the cams and adding long tubes (and a dyno tune). From all the various postings and articles I have read anticipate rwhp around 280-300 is pretty typical at this point. That would mean somewhere between 325-360 brake hp. (figuring a 15-17% loss w/ a 5spd.)


Most of what I read suggests that the stock 19lb. injectors are pretty much maxed out at the stock levels (85% D/C at about 39psi). The fact that Ford increased the size to 21lb. for the 03-04 years also kind of supports that theory, however there are also or postings of guys who have performed cam swaps and seem to be running just fine with the stock 19lb (along w. other supporting mods).


I do understand the concept that the flow rate will increase if the fuel line pressure is increased(w/ tune), but it leads me to ask what is the correct approach.
I am looking to make safe power, good drivability, and not lean out the torque curve any, but honestly don't want to spend a few hundred dollars if it is an absolutely waste of money.

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post #2 of 22 (permalink) Old 08-20-2019
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I'm assuming you have the formula for calculating the injector size/flow demands......if not here it is...


Maximum HP Times BSFC (.5)
multiplythe number of injectors by .8

(BSFC= Brake Specific Fuel Consumption)


The 19lb units will flow a lot of fuel and it is also much dependent upon the ecm….as it can shorten or lengthen the spray duration to recude or increase the overall delivery......although you should run the specific calc's for your specific engine, in general, unless you significantly change the cid (such as stroking the engine), increase rpm's by 1,000+ or instala blower, etc.....the 19lb units should be fine.

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post #3 of 22 (permalink) Old 08-20-2019 Thread Starter
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Originally Posted by Beechkid View Post
I'm assuming you have the formula for calculating the injector size/flow demands......if not here it is...


Maximum HP Times BSFC (.5)
multiplythe number of injectors by .8

(BSFC= Brake Specific Fuel Consumption)


The 19lb units will flow a lot of fuel and it is also much dependent upon the ecm….as it can shorten or lengthen the spray duration to recude or increase the overall delivery......although you should run the specific calc's for your specific engine, in general, unless you significantly change the cid (such as stroking the engine), increase rpm's by 1,000+ or instala blower, etc.....the 19lb units should be fine.


Thanks for answering Beechkid.
No, I am not looking at stroking, forced induction, or increasing RPM much beyond 5,500.
My fear in just going to a local speed shops and asking "hey do I need to give you more money, for this to be correct", will almost automatically result with "yes".


Yes, I have been using the above mentioned formula as my basis.
So from your experience, safe to assume that I would not significantly be reducing the lifecycle of my stock fuel system (injectors, rails, pump, etc.) to accommodate the increase?
Also I have read a couple threads, where guys have mentioned that not following the brake hp x BSFC formula (for sizing injectors) will result in a smaller torque curve, is there any truth to this?
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post #4 of 22 (permalink) Old 08-20-2019
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I don't think you will reduce the life cycle on the components really. You won't be running around "maxed out" all the time. I doubt you'll be redlining everywhere you go.
But it might not be enough fuel to fuel it with 19's.
I'm running 19's and an FMU, which closes the fuel return line at WOT to increase the fuel pressure. Making 332 at the wheels. Been doing it for seven years or so now.
Not that any of this helps you really though. I'd plan on larger injectors, but talk to the tuner prior to ordering.
Mine recommended 42# if I wanted get rid of the FMU. I asked him if it would improve power if I went with 42's and he said no, but the air/fuel ratio line on the graph would be a little straighter. He didn't mention the tq curve. My curve is pretty flat from 3k to redline.
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post #5 of 22 (permalink) Old 08-20-2019 Thread Starter
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Quote:
Originally Posted by 90lxwhite View Post
I don't think you will reduce the life cycle on the components really. You won't be running around "maxed out" all the time. I doubt you'll be redlining everywhere you go.
But it might not be enough fuel to fuel it with 19's.
I'm running 19's and an FMU, which closes the fuel return line at WOT to increase the fuel pressure. Making 332 at the wheels. Been doing it for seven years or so now.
Not that any of this helps you really though. I'd plan on larger injectors, but talk to the tuner prior to ordering.
Mine recommended 42# if I wanted get rid of the FMU. I asked him if it would improve power if I went with 42's and he said no, but the air/fuel ratio line on the graph would be a little straighter. He didn't mention the tq curve. My curve is pretty flat from 3k to redline.
These answers are exactly the reason, I asked here first. I will definitely get input from the tuner, but just don't want to get hooked on a sales pitch and wind up spending more than I can afford (for nothing). It really sounds like with my plans the stock fuel system will be just fine. Thanks for answering LX.
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post #6 of 22 (permalink) Old 08-20-2019
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Originally Posted by 90lxwhite View Post
I don't think you will reduce the life cycle on the components really. You won't be running around "maxed out" all the time. I doubt you'll be redlining everywhere you go.
But it might not be enough fuel to fuel it with 19's.
I'm running 19's and an FMU, which closes the fuel return line at WOT to increase the fuel pressure. Making 332 at the wheels. Been doing it for seven years or so now.
Not that any of this helps you really though. I'd plan on larger injectors, but talk to the tuner prior to ordering.
Mine recommended 42# if I wanted get rid of the FMU. I asked him if it would improve power if I went with 42's and he said no, but the air/fuel ratio line on the graph would be a little straighter. He didn't mention the tq curve. My curve is pretty flat from 3k to redline.
These answers are exactly the reason, I asked here first. I will definitely get input from the tuner, but just don't want to get hooked on a sales pitch and wind up spending more than I can afford (for nothing). It really sounds like with my plans the stock fuel system will be just fine. Thanks for answering LX.
What about the fuel pump? Is it standard practice to upgrade the pump for your list of mods, or will the stock one suffice?

Copied from the FORD RACING PERFORMANCE PARTS catalog:

PROPERLY SIZING FUEL SYSTEM COMPONENTS

Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”

Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.
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post #7 of 22 (permalink) Old 08-20-2019 Thread Starter
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So based on that formula, I am coming up with the stock 130lph pump being good to handle up to 371 brake horse.
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post #8 of 22 (permalink) Old 08-20-2019
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Originally Posted by SonicBlue02 View Post
So based on that formula, I am coming up with the stock 130lph pump being good to handle up to 371 brake horse.
I once saw a gutted pi swap mustang with aftermarket cams running down the 1/8 mile. I’m not sure what injector size he was running, but judging by the rest of the “build,” or lack there of, I betcha he had the stock pump in there. It was awhile back but if remember right I think he said it made 260 or so rear horse. But anyway, his didn’t blow up. I tried to race him but I screwed the pooch on the start.
https://m.youtube.com/watch?v=0Jp3S-nALIQ
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post #9 of 22 (permalink) Old 08-20-2019
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Quote:
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So based on that formula, I am coming up with the stock 130lph pump being good to handle up to 371 brake horse.
Pump capacity becomes a non-issue unless the other variables are included:

Let's assume a few things: first, I'm somewhat knowledgeable about OHV 5.0HO results, but not later OHC engines. Ford saw fit to use 19# injectors with 5.0HOs in Mustangs from somewhere in the late 1980s until 1993. During that time the same engines in non-HO trim used smaller capacity injectors, 15 or 16# or something similar, especially in F-Series trucks. One might think the truck engines would be called upon more stringently, or often, than automobile engines, no?

Enter 1993 5.0HO in Cobra: 24# injectors. Now given the very modest increase in rated HP from 225 to 245, much of which might have been attributable to slightly increased valve duration, but also roller rocker arms. So, the 24s were open for shorter duty times, all else unchanged, than 19s. Ford Motorsports sold kits in the '90s intended for 351W use, among others, which included 24# injectors, a new Mass Air Unit, and a new PCM. I used that kit to retrofit a 351W, carburetted, in a 1968 Mustang; it worked out very well, using the GT-40 intake manifold.
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Originally Posted by SonicBlue02 View Post
So based on that formula, I am coming up with the stock 130lph pump being good to handle up to 371 brake horse.
Pump capacity becomes a non-issue unless the other variables are included:

Let's assume a few things: first, I'm somewhat knowledgeable about OHV 5.0HO results, but not later OHC engines. Ford saw fit to use 19# injectors with 5.0HOs in Mustangs from somewhere in the late 1980s until 1993. During that time the same engines in non-HO trim used smaller capacity injectors, 15 or 16# or something similar, especially in F-Series trucks. One might think the truck engines would be called upon more stringently, or often, than automobile engines, no?

Enter 1993 5.0HO in Cobra: 24# injectors. Now given the very modest increase in rated HP from 225 to 245, much of which might have been attributable to slightly increased valve duration, but also roller rocker arms. So, the 24s were open for shorter duty times, all else unchanged, than 19s. Ford Motorsports sold kits in the '90s intended for 351W use, among others, which included 24# injectors, a new Mass Air Unit, and a new PCM. I used that kit to retrofit a 351W, carburetted, in a 1968 Mustang; it worked out very well, using the GT-40 intake manifold.
Do what now?
The HO made more power than the trucks so they got larger injectors. The cobra made more power than the standard ho so they got larger injectors still. The more power the engine was rated the larger the injector. There’s the variable.
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Thanks for answering Beechkid.
So from your experience, safe to assume that I would not significantly be reducing the lifecycle of my stock fuel system (injectors, rails, pump, etc.) to accommodate the increase?
Also I have read a couple threads, where guys have mentioned that not following the brake hp x BSFC formula (for sizing injectors) will result in a smaller torque curve, is there any truth to this?
The short answer.....Yes..a good assumption or foundation to start from...I would initially run with what you have and because with all likelihood you will have to have a "real Tech" tune the engine, see what they find so to speak......let's face it, injectors are easy to change and the 19lb units are not going to create any lean type condition (especially on initial startup) to cause any damage....and the potential for A/F damage would not be likely until you get into the upper rpm ranges/loads, etc...…. all of which the "tuner" is going to bring the engine up in segments (typically 1000 rpm at a time) to make sure all is good before going the next level. Why spend $ on parts you likely won't need....and you're right....most of the "performance Shop" counter staff today just read the PR material and push sales.....unfortunately.


With regard to the torque curve (ie "power band"), that is controlled by the cam.....the band can be slightly varied (300-500 rpm)with additional cam timing adjustments (not recommended on street engines as this take a bit of time doing valve/piston clearance checking...unless the cam mfg directs you to do it)….. and is secondly supported by #1 ignition timing and #2 fuel.....but this is all secondary to the cam which is the "heart or lungs" of the engine...telling it when to breathe and how much to breathe......

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The short answer.....Yes..a good assumption or foundation to start from...I would initially run with what you have and because with all likelihood you will have to have a "real Tech" tune the engine, see what they find so to speak......let's face it, injectors are easy to change and the 19lb units are not going to create any lean type condition (especially on initial startup) to cause any damage....and the potential for A/F damage would not be likely until you get into the upper rpm ranges/loads, etc...…. all of which the "tuner" is going to bring the engine up in segments (typically 1000 rpm at a time) to make sure all is good before going the next level. Why spend $ on parts you likely won't need....and you're right....most of the "performance Shop" counter staff today just read the <acronym title="Page Ranking"><acronym title="Page Ranking"><acronym title="Page Ranking">PR</acronym></acronym></acronym> material and push sales.....unfortunately. [IMG class=inlineimg]/forums/images/AllFordMustangs-vbtoucan/smilies/tango_face_wink.png[/IMG]


With regard to the torque curve (ie "power band"), that is controlled by the cam.....the band can be slightly varied (300-500 rpm)with additional cam timing adjustments (not recommended on street engines as this take a bit of time doing valve/piston clearance checking...unless the cam mfg directs you to do it)….. and is secondly supported by #1 ignition timing and #2 fuel.....but this is all secondary to the cam which is the "heart or lungs" of the engine...telling it when to breathe and how much to breathe......
The money smart answer...
Injectors might be easy to change, but if you gamble wrong and go too small you'll probably end up paying double.
Tuners pretty much just tune. They want you to be ready to go when you're on the dyno. So if you get up there and run out of fuel with the 19's you'll pay for that tuning session and they'll tell you to come back with larger injectors. Then you'll pay for that session too. It'll probably run between $500-$700 a session. If they happen to have a set of larger injectors on hand you'll have to pay for their markup. The likelihood of getting them installed and re-tuned that same day is probably pretty slim. It'll be someone else’s turn on the dyno once you get of, and the shop will probably be working on other cars to where they won't have time to swap them. You could do it in the parking lot but the tuner man won't wait on you I don't imagine.
As far as only running out of fuel at the upper rpm range, well, that's pretty much the only area the tuner will be tuning. They tune wide open throttle from like 3k to redline.
Yes I have 19# injectors and over 300 hp, but they wouldn't be enough if I didn't have the fmu spiking the fuel pressure way up.
They can tune for injectors being too large but I don't think too much can be done if they're too small.
Call the tuner and see what they like to use. Don't look at it as an "up sale," since you don't have to buy them from them.
One a side note, say you use 24's and install at home prior to going to the dyno, I'm not sure if it'd run well enough to get you there or not.
But at any rate I’d plan for the injectors to be in the budget until they tell you otherwise when you make the appointment.

Last edited by 90lxwhite; 08-21-2019 at 07:07 PM.
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post #13 of 22 (permalink) Old 08-21-2019 Thread Starter
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Fortunately I do have (2) tuners in close distance. I have yet to talk to either but am waiting till I am closer to getting things moving before I talk to them. One of them is Anderson Ford (who I know have a very good rep with all motors mustang), I know I would prefer them to do the tunning however I am not leaning towards their cams or brand of lt headers, and don't know if that will cause an "attitude" about the whole thing. The other outfit is literally about 5 miles away. They are called Redline Motorsport and they are all pretty serious circuit drag racers (3 of the 4 all being mustangs), they also specialize in Holley EFI kits (so I would think they have this fuel thing figured out). I personally know I could handle the injector swap myself, I am just under the impression that oversizing (for where I am right now) could really "f" up the ecu, and like LX mentioned I may not even be able to make it 5 miles down the road without a tow. Despite how much I would like to do the cam swap myself, I just really don't think I should take this on myself and figured if larger injectors are needed, the time to do them is with the cams.
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post #14 of 22 (permalink) Old 08-22-2019 Thread Starter
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Quote:
Originally Posted by 90lxwhite View Post
I once saw a gutted pi swap mustang with aftermarket cams running down the 1/8 mile. I’m not sure what injector size he was running, but judging by the rest of the “build,” or lack there of, I betcha he had the stock pump in there. It was awhile back but if remember right I think he said it made 260 or so rear horse. But anyway, his didn’t blow up. I tried to race him but I screwed the pooch on the start.
https://m.youtube.com/watch?v=0Jp3S-nALIQ

Jeeze LX, what happened there?
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The money smart answer...
Injectors might be easy to change, but if you gamble wrong and go too small you'll probably end up paying double.
Tuners pretty much just tune. They want you to be ready to go when you're on the dyno. So if you get up there and run out of fuel with the 19's you'll pay for that tuning session and they'll tell you to come back with larger injectors. Then you'll pay for that session too. It'll probably run between $500-$700 a session. If they happen to have a set of larger injectors on hand you'll have to pay for their markup. The likelihood of getting them installed and re-tuned that same day is probably pretty slim. It'll be someone else’s turn on the dyno once you get of, and the shop will probably be working on other cars to where they won't have time to swap them. You could do it in the parking lot but the tuner man won't wait on you I don't imagine.
As far as only running out of fuel at the upper rpm range, well, that's pretty much the only area the tuner will be tuning. They tune wide open throttle from like 3k to redline.
Yes I have 19# injectors and over 300 hp, but they wouldn't be enough if I didn't have the fmu spiking the fuel pressure way up.
They can tune for injectors being too large but I don't think too much can be done if they're too small.
Call the tuner and see what they like to use. Don't look at it as an "up sale," since you don't have to buy them from them.
One a side note, say you use 24's and install at home prior to going to the dyno, I'm not sure if it'd run well enough to get you there or not.
But at any rate I’d plan for the injectors to be in the budget until they tell you otherwise when you make the appointment.
Good points...with this additional......The OEM software system is designed to adjustthe fuel mixture up to 25% on the 2000+ mod engines.... so IMHO, given we are not changing CID via actual displacement or via 1000+ rpm increase, IMHO, it would be very difficult for the 19lb injectors to underflow for general/normal type driving, staying out of the upper range until the A/F ratio can be verified......on the other hand, with 24 lb injectors and software programmed to think their 19lb units, cylinder washing is more likely.....and would be of a much greater concern to me and the damage/contamination resulting.


BTW, their are plenty of well known tuners who can remotely view in general driving conditions what is going on and adjust/tune from there..... and for what you are doing, you won't be spending any more $ that what has already been discussed....


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