WHAT INJECTORS DO I NEED

dragin92gt · Dec 20, 2008

89 gt
331,h-beams, flat tops,
victor jr heads, p/p
victor jr 5.0 intake, port matched
aod
3.73
x cam(soon to be AFM of some sort)
255lph fuel pump

car had 19lbr's in it when i got it, ran lean as heck, added 24's still runs lean, so ima thinking since ive saved some dough, ill order some 30's or 42's

Foxfan88 · Dec 20, 2008

i'd say 36s or 42s should be a good match.

Cougar5.O · Dec 20, 2008

I go with 36's or 42's - 30's ain't gonna cut it either.

jrichker · Dec 21, 2008

Injector HP ratings: divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines.

Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

304 HP x .85 = 258 HP
385 HP x .85 = 326 HP
480 HP x .85 = 408 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See Automotive Performance Software / Interactive JavaScripts Calculators to get the calculators used in these examples.

Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Grn92LX · Dec 22, 2008

jrichker · Dec 22, 2008

How do you know that the engine is running lean? Do you have a broadband air/fuel gauge or did you get a custom dyno tune?

dragin92gt · Dec 22, 2008

no i honestly am just going by the glow in the headers. but i did order the innovative db3796 today so when it starts warming up i will know for sure. then i can order some injectors

Cougar5.O · Dec 22, 2008

Oh fer cryin' out loud - glowing headers is not how you tune a car! And glowing at idle tells you nothing about whether your injectors are sized properly, only that your MAF may not match your injectors, is defective or your timing is way retarded.

dragin92gt · Dec 23, 2008

well f 4 cryin out loud lol

as soon as it starts to warm up here, which may never happen, i will try adding a little timing at a time and watch the wideband to make sure the a/f ratio stays good

jrichker · Dec 23, 2008

jrichker said:
How do you know that the engine is running lean? Do you have a broadband air/fuel gauge or did you get a custom dyno tune?

dragin92gt said:
no i honestly am just going by the glow in the headers.

Next time I see one of these "I'm running lean" posts, I will ask this question first...

2000xp8 · Dec 23, 2008

FastDriver · Dec 23, 2008

You can tune any of these injectors to make the power but the 24s will need some pressure to do it. 30s will get the job done. If it were me I'd go with the 36s if I was staying N/A and with the 42s if I wanted room to grow.

Chris

dragin92gt · Dec 24, 2008

i think ima going to find some 42's because ive often thought about a lil spray. but i may just do the 30's and drive the piss outa it

thebullschmidt · Dec 25, 2008

go with the 42's and spray

91notch5.0 · Dec 27, 2008

i'd go 42. i'm ditching my 24's so i can spray too lol.

ID89GT · Dec 27, 2008

You could get a scanner and see what your 02 sensors are doing with the fuel trim numbers to see if it really is running lean or not..

jrichker · Dec 27, 2008

ID89GT said:
You could get a scanner and see what your 02 sensors are doing with the fuel trim numbers to see if it really is running lean or not..

The 86- 95 EFI Mustangs do not have this ability. There is no real time fuel trim data available via a scanner. Codes are all you get and thats all. If you want real time fuel trim data from the computer, you need a Tweecer.

joel5.0 · Dec 27, 2008

jrichker said:
The 86- 95 EFI Mustangs do not have this ability. There is no real time fuel trim data available via a scanner. Codes are all you get and thats all. If you want real time fuel trim data from the computer, you need a Tweecer.

SN95's are the exception, they do have datastream capabilities.... including short and long term fuel trim data/ bank. Did two '95 TwEECer tunes, using a a WB + centering STFT and LTFT values near 0% for both banks using my Genisys scanner.

dragin92gt · Jan 13, 2009

ok last nite i was looking through some old magizines. in one of the recent 5.0 and superfords, they did a h/c/i change on a 90 or 91 gt. i got 2 reading more on the story, and on the statistic page they had SUPPOSEDLY only ran 32psi fuel pressure.

i was wondering if anyone thought that this could be the issue with my 89. it has a 255lph pump, aeromotive fuel rails, 24lb injectors, and i for the life of me cannot get it to run right. i havent got the wideband hooked up yet, been to dam cold

lickem · Jan 13, 2009

ive got a 393 stroker, f cam, windsor jr world products heads, edelbrock performer intake, and everyone told me i needed 42's so i went 42's. i cant get it to idle worth a crap, cant get it to not stumble throughout the rpm range, i lowered my fuel pressure to 37psi, have checked everything atleast 3 times and im still getting way to much fuel! unless you are going to have it tuned to have the injector cycles lowered id go 30's if i were you. bigger isnt always better.

check your timing if your headers are glowing, if you timing reads right and the headers are still glowing then maybe you should check your balancer to see if maybe the elastomeric material is bad and the balancer isnt reading right.

did you put the motor together? maybe it has an aftermarket timing set and whoever installed it retarded it??

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