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Discussion Starter · #1 ·
Im putting on a pi intake and 24 lb injectors. I haves sniper tuner or whatever it is, and im completely rebuilding my engine. Should i retune it or would it be fine how it is?
 

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Your maf has to match up with your injectors if they are not already.
 

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Depends on what you mean also by rebuilding the engine. For example if your gonna just throw stock parts back in them u should be fine how you are I mean to get the most out of your parts you should get it tuned to match but it won't be horrible however if you mean rebuilding the motor with performance stuff like cams and different compressions pistons etc your deff gonna need a new tune.
 

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Discussion Starter · #4 ·
Nah none of that. I might get pi heads later on but they're too expensive right now. Gotta save a few paychecks and all. But i have a pi intake and lt headers and 24 lb injectors so i dont know if i need another one!
 

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The headers it's not a necessity to have a new tune granite it will run better with a matched tune but the injectors u may need to retune because they go by a percentage of fuel and with bigger injectors your gonna dump more fuel because your car still thinks u have the smaller injectors.
 

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OP, yes you will need a tune. Your engine will run very rich at WOT, and may throw "rich" DTCs in normal closed loop operation...


As to MAFs, they do not have to "match up" with injectors, So-called "calibrated" MAFs are a kludge left over from the early days of EFI when tunes could not be easily (or at all) modified, and a MAFs output curve would be modified to allow a given stock tune to work with larger injectors--this is done by lying to the ECU about how much air is flowing at lower air flows. This causes the ECU to calculate shorter injector pulse widths that it would, causing the engine to not run rich because of the larger injectors.

At high loads and WOT a "calibrated" MAF lies less or not at all so that more fuel is injected.

More about "calibrated" MAFs and why they suck here...

On our cars there are only four scalar values that need to be changed to accommodate larger (or smaller) injectors:

  • Fuel Injector Low Slope - lbs/h at short pulse wdiths
  • Fuel Injector High Slope - lbs/h at other pulse widths
  • Fuel Injector Breakpoint - the point (in μlb/revolution) to switch to using the low slope lb/h
  • Fuel Injector minimum Pulsewidth - the shortest allowable pulse width (in ms)

The MAF (the stock 80 mm MAF can support up to 400 fwHP running n/a), and the MAF transfer function need to be changed.
 

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Discussion Starter · #8 ·
Wow thanks for then info cliffyk! I appreciate it! Ill tune it with my sniper tuner i have once i get it all done with! Hopefully it makes a noticeable difference! I havent driven my stang in about a year so itll definitely be an amazing first ride!
 

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Wow thanks for then info cliffyk! I appreciate it! Ill tune it with my sniper tuner i have once i get it all done with! Hopefully it makes a noticeable difference! I havent driven my stang in about a year so itll definitely be an amazing first ride!
What package/version of "Sniper" do you have (there has been no Sniper tuning for 4+ years¹). Is it Special Forces or Commando?

If SF does the "Tell us..." screen look like this:

version 1.x


or like this:

version 2.x


With either I suggest you download the upgrades; available here for v 1.x, and here for v2.x.

The most important part of the upgrades is that they permit improved fine tuning of the injector slopes...

---------------------------------
¹ - The company and products have been Delta Force Tuning since Holley claimed they had trademarked the brandname Sniper some time back--that is why Holley Performance NOS Products will get you to Holley's Nos website.
 

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Discussion Starter · #10 ·
Ill have to put it in and check but im 99 % sure its the second picture. Version 2 or whatever that is.
 

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So cliffky what your saying is that if I upgrade my injectors I don't need to do anything to the maf?
 

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So cliffky what your saying is that if I upgrade my injectors I don't need to do anything to the maf?
That is correct; assuming that:

  • Your MAF has sufficient capacity to measure your engine's air flow without "pegging" (reaching 4.9V output). The stock 80 mm MAF can meter up to 2450 lb/h--at 12.5:1 AFR running n/a. In theory that is enough for 400 flywheel HP, approximately 340 at the wheels. In practice people have gone to 375 rwHP or a bit better with the stock MAF;

  • You alter your tune to set the proper slope, breakpoint and minimum pulse for the new injectors;

"Calibrated" MAFs, those "matched to the injectors" are only needed if you cannot, or choose not to, do things properly and change the tune.

I am running 24 lb/h injectors, with the stock MAF, the only changes were to those scalar values I referenced above and as shown below:



The highlighted values are those for the 24 lb/h injectors, the others are the stock settings.

Ford's recommended value for the 24 lb units high slope was 24.3 lb/h; however I found this was too low, making the engine run rich, The value displayed in the table (25.6 lb/h) is what i arrived at after a few WOT runs...
 

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That is correct; assuming that:


[*]Your MAF has sufficient capacity to measure your engine's air flow without "pegging" (reaching 4.9V output). The stock 80 mm MAF can meter up to 2450 lb/h--at 12.5:1 AFR running n/a. In theory that is enough for 400 flywheel HP, approximately 340 at the wheels. In practice people have gone to 375 rwHP or a bit better with the stock MAF;

[*]You alter your tune to set the proper slope, breakpoint and minimum pulse for the new injectors;


"Calibrated" MAFs, those "matched to the injectors" are only needed if you cannot, or choose not to, do things properly and change the tune.

I am running 24 lb/h injectors, with the stock MAF, the only changes were to those scalar values I referenced above and as shown below:

The highlighted values are those for the 24 lb/h injectors, the others are the stock settings.

Ford's recommended value for the 24 lb units high slope was 24.3 lb/h; however I found this was too low, making the engine run rich, The value displayed in the table (25.6 lb/h) is what i arrived at after a few WOT runs...
Oooo now I know what you mean Iam srry my car is obd1 so it is not as easy to tune it as it is for you guys cause there is no handheld tuners for my car I was looking at the sct 4 bama chip on am has any of you guys heard about that?
 

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Oooo now I know what you mean Iam srry my car is obd1 so it is not as easy to tune it as it is for you guys cause there is no handheld tuners for my car I was looking at the sct 4 bama chip on am has any of you guys heard about that?
The 4-tune chip requires an EEC-IV or EEC-V PCM, with the J3 port--what PCM/ECU are you running that is OBD1?
 

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The 4-tune chip requires an EEC-IV or EEC-V PCM, with the J3 port--what PCM/ECU are you running that is OBD1?
Iam pretty sure it works with the stock ecu and stock PCM and my car comes obd1 it is a 94 gt
 
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