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injector upgrade question

6K views 21 replies 4 participants last post by  SonicBlue02 
#1 ·
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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#2 ·
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.
 
#3 ·
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?
 
#4 ·
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.
 
#5 ·
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.
 
#8 ·
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
 
#13 ·
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.
 
#20 ·
Yeah, I did come across that one some time ago. I dunno, I purchased this car 5 years ago with the original intentions of only doing pretty much what I have done up to this point and just enjoying it. I do enjoy her every summer (stored in the winters), but for the past 3 years or so, every year I always start thinking about cams and long tubes, and then I talk myself out of it.


I have thought about the F/I route also and always talk myself out of that one as well.
In a perfect world, I think what I am really looking for is an N/A motor that puts down similar power to a Mach 1 (just exchanging some of the higher RPM power for a little lower torque), pretty similar to that advertisement I posted.
I would have gone with a Mach if they only had made a convertible. I did look at some cobra's also (non-termi), but I am one weird guys that prefers the look of the GT to the cobra.


I think what I am chasing after is obtainable (at least I hope so), I am just trying to find the best recipe to get there and hopeful to not waste a whole lot of time or money in the process.


Who knows LX, I may wind up talking myself out of this again....lol
 
#22 ·
I completely agree with you that the best dollar for horsepower investment a 2v owner can make is to go FI. I have looked into KB, torque tech, saleen, and centri's (i would have to go centri or remove my STB (and don't really want to do that). Shop cost will play a big factor. I know how much a pita long tubes are to put on, so I would payout for that, would plan to use my current O/R/H, but I am not a welder so I would need them to modify it to fit. If the end result put me closer to the 350ish brake horse, i think I can live w/ a 2k investment to get there. Now if the price is 25 or up. Or if we are talking 260-270 rwhp is all I get, it changes everything. Truth is there is always something faster, hell by the next decade if electrical cars take over, we may be complaining about how slow a hellcat is. IMO it wont matter, I still like my mustang better. Hell there are a lot of old muscle sports cars that are not as fast 0-60 as our 2v's that are worth a whole lot more $$ and are still BA and desireable. the reason i am leaning more n/a is because i am trying to maintain a real stock look and feel to everything. I guess i am trying to do everything kind of like it got ordered from Ford this way. I know its modified, any other mustang guy will know its modified, but that is why i shy away from a blower. Trust me man, I know i'm an odd ball...lol.
 
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