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19 Lbl injector Limits

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Old 09-06-2013, 06:37 AM   #1
yurizx6r
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Default 19 Lbl injector Limits

Hey guys, I know this is sort of a grey area question that has been asked before, but I was just wondering how much hp I can have before I have to upgrade my fuel injectors. From what I read, the most consistent answer is around 280 hp.

My set up is this: BBK CAI, C&L 73mm MAF, 70mm TB, American Muscle Bama chip, and a full exhaust (long tube, off road H, and flowmasters catback). I would like to put in either an Edelbrock or trick flow intake manifold. Can I do the intake manifold without having to upgrade my fuel injectors? Will this hurt the motor if I do not? I know I have to upgrade when I do heads, but I need to save up more money because when I do the heads I want to redo the entire fuel system, cams, timing chain, etc. etc.

Thanks for any help in advance!
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Old 09-06-2013, 06:58 AM   #2
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you have no real power making mods to warrant anything other than 19's right now
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Old 09-06-2013, 07:05 AM   #3
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You'll be fine with 19's, save your money.

I'm at 300 rwhp right now and still running 19's. They are maxed out on duty-cycle at redline, but my wideband shows its not lean so I'm right at the limit. They can take short squirts at max duty cycle, just not long periods like in road racing. I've been running this car for 6 yrs as is and haven't had a problem. Yes, I'll be putting in 24's just for the safety margin. But you'll be fine with 19's.
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Old 09-06-2013, 07:21 AM   #4
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Perfect! Thanks! Just curious, how did you get to 300RWHP? I know once I do heads it's a good idea to upgrade, but I don't want to right now if I do not have to.
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Old 09-06-2013, 08:12 AM   #5
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I can't take complete credit for this motor, p.o. must have did his homework because it's a basic 306 with all bolt ons, letter cam and ported E7's. When I first bought the car it had a built AOD with a stall, dyno'd 270/300. All I did was swap to a T5, added a fender mount cai, and electric fan. Car then put down 300/316. It shouldn't be making those #'s, but I think it's one of those things where everything is working together. Good luck with yours, they are fun cars to play with.
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Old 09-06-2013, 03:01 PM   #6
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Both of these guys are right on with their advice! The factory 19lb fuel injectors are plenty for this setup. You'll probably be able to use them with aftermarket heads too. However, add a lumpy camshaft to the mix and you should upgrade to the 24lb'ers.

Have fun with your build! These push-rod 5.0's have always been one of my favorite Mustang engines.

Shane
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Old 09-09-2013, 06:25 PM   #7
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It's worth mentioning that the 280HP limitation is right on with the typical injector calculation formulas, but that this is 280 gross FWHP, not net, not rear wheel. That's just the engine, on a dyno, with no belt-driven accessories being attached to the engine.

You could exceed the 280 mark, but the duty cycle rises above the desired 80%. Why 80%? Because the injector driver circuit needs time to cool off or it will overheat. And because anything over about 90% doesn't really allow for proper fuel control. And finally, because all of the fuel is supposed to be injected onto the back side of a closed intake valve. At some point, that valve opens, and the fuel would be injected into an open intake valve, which is not ideal for complete atomization.
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Old 09-10-2013, 05:26 AM   #8
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Well as it turns out. Today I am picking up an Edelbrock Performer upper and lower intake manifold that comes with 24lbl injectors. So my total engine mods would be CAI, 73mm MAF, 70MM TB, Edelbrock intake manifold, bama chip from American Muscle, and a full exhaust. Should I put the 24 pounders on or leave the 19 pound injectors on?
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Old 09-10-2013, 06:55 AM   #9
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If the maf is calibrated to the 24's, definitely. Won't hurt you at all. Your still well below the limit of the 19's, maybe 220 at the wheels. If your maf is still calibrated for the 19's, leave them in. Your safe either way. Good luck.

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Old 09-10-2013, 07:01 AM   #10
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Well as it turns out. Today I am picking up an Edelbrock Performer upper and lower intake manifold that comes with 24lbl injectors. So my total engine mods would be CAI, 73mm MAF, 70MM TB, Edelbrock intake manifold, bama chip from American Muscle, and a full exhaust. Should I put the 24 pounders on or leave the 19 pound injectors on?
IMO it's still a waste, cause when you actually do some real mods like heads and cam, it'll all have to come back off again.
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Old 09-10-2013, 07:24 AM   #11
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You are correct, it is sort of a waste because the heads will limit the hp gain from the manifold, but it will be about 2 years or so before I do the heads, cams, timing chain, pistons, etc. Until then, I'm just wanting a little bit more tb response and fun for cheap. I'm about to go into the masters program at my college, so I cannot afford to put out 2,000 bucks on the things I want just yet (I don't want to buy that stuff used).
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Old 09-10-2013, 07:40 AM   #12
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What gears are you running? If your looking for the best bang for buck / butt-dyno improvement, fun-meter pegged, can't beat a gear swap. That's if you still have stockers. I know that's going a different direction than engine mods, but gears will feel like you have 300 hp. You said moneys tight and your just looking for "fun for cheap",so just a suggestion.

Last edited by 88 orangepeel notch; 09-10-2013 at 07:44 AM.
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Old 09-10-2013, 07:53 AM   #13
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I have the stock 308 gears. I have some suspension upgrades, so I'm good there, I'm just looking for that 1/4 mile fun.
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Old 09-10-2013, 07:56 AM   #14
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I was actually thinking of going 355 or 373 gears, but I'm worried about having to consistently shift so quick. Big difference on that?
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Old 09-10-2013, 08:47 AM   #15
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OH CRAP !!! You have to get those gears out of there. Since your alittle above stock power (with more to come)…… I'd do the 3:73's. You WON'T be dissappointed on spending that money. Or if your really cheap like me, keep an eye on Craigslist for a complete rearend with the gears already done. Plug and play then, as long as you know what your buying.

Yeah the intake will help alittle, but nothing compared to a gear swap. You'll be smiling till your face hurts, seriously.

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Old 09-10-2013, 08:52 AM   #16
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Why "OH CRAP?" That much of a difference?
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Old 09-10-2013, 08:57 AM   #17
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YES YES YES, You won't believe the difference. You cannot go wrong with gears. Well you may loose a mpg or 2, but still way worth it. The shifting will not bother you.
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Old 09-10-2013, 10:52 AM   #18
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YES YES YES, You won't believe the difference. You cannot go wrong with gears. Well you may loose a mpg or 2, but still way worth it. The shifting will not bother you.
Gears are without a doubt the biggest bang for the buck. If you are worried about overstepping the gear (especially if running stock size tires), a 3.55 will do nicely. Typically, guys run 3.73 with a 5 spd or 4.10 with an auto... but they will have taller and sticky tires too.

Using MAFs that are calibrated for injector size is right up there with leeching to cure ailments. In modern times, we properly calibrate for the injector size by changing the tune. Ford Racing gives us the injector characterization data we need for all Ford Racing injectors. Or if they are OEM Ford injectors, we can pull that data out of a stock tune in a car that came with those injectors.
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Old 09-10-2013, 01:01 PM   #19
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Well I have a T5 transmission in it with 255/40R17 tires (Nitto 555's), so I guess the 3.55's? As for the injectors, could I put the 24's on and just get the calibration tube (C&L MAF) for the 24lbl injectors? Or would I need an adjustable fuel pressure regulator?
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Old 09-10-2013, 01:25 PM   #20
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Using a calibrated MAF to compensate for injector size changes works ok for fox bodies, with 24# injectors. Anything bigger than that, and it gets problematic.

The better way to do it is to tell the computer (via a chip) that you've got 24# injectors. Ford uses a specific set of data tables to describe to the computer how to control the injectors. It's not just "24#". It's low slope, high slope, breakpoint, minimum pulsewidth, and most importantly voltage compensation tables. Each injector is controlled uniquely, and saying 24# (or using a calibrated MAF) only addresses the static flow rate setting (called hi slope).

Since the part throttle timing tables are based on load, and load is based on airflow versus engine size, and airflow is based on MAF readings, and MAF readings are being skewed by a calibrated meter, I don't care to ever use calibrated meters for that purpose.

We still use them for their larger airflow housing and increased electronic range. We just don't use them in the way they were intended, which was to "lie" to the computer about airflow so that the computer will command a lesser pulsewidth the the injectors (which were also changed without the computers knowledge in this case).

What we really want is to use the larger MAF housing, if NECESSARY use the increased electronic range of the larger MAF, and then properly calibrate for both the MAF and the injectors in the tune.

It's like this. We don't tell a calculator to do 12 plus 4 so we can an answer of 16, if the real numbers are 8 + 8 = 16. Sure, you can trick it with limited success... but why would you want to? Let that calculator do the real math with the real numbers. In tuning, there are unintended consequences to using the wrong numbers to come up with the right answer! And spark timing is that consequence.

As we increase the size of the meter electronically (using a calibrated MAF), we are basically making the computer think there is less airflow coming in. The computer then calculates less load, which calls for MORE spark. And the bigger the MAF calibration trick, the bigger the problem. So in effect, a calibrated MAF adds more spark timing at part throttle. This might not be noticeable with a simple 24/19ths MAF calibration (24# injectors where a 19# is supposed to be). But try a 30 or 42# injector, and drivability will quickly suffer.

An adjustable fuel pressure regulator is not necessary, unless you are trying to trim air/fuel ratios on your wideband, without tuning.
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Old 09-10-2013, 01:25 PM
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