INJECTOR HELP

94excoupe said:

i need to know what size injectors to run and any possible upgrades to help. nothing crazy though.
mods:
stock 302 block
afr165 heads
b303 cam
trick flow intake
1.6 rr
70mm throttle body
msd ignition
under drives
stock cobra inj ecu and mass air
3.73 gears
lake wood shocks
tubular control arms

i have 30 lb injectors and 80mm pro m mass air that could be installed.just dont know which is better. also have crane 1.7 rr. any help is appreciated.

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If you plan on getting it dyno tuned then i would go with the 30s and pro m. but if tuning isnt in your budget then keep the 24's i think u will be fine with those for now

Injector HP ratings:

Calculating injector size: the first thing you need to do is to project the max HP you think you will make.

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



Other fuel system components you'll need with bigger injectors
Remember that if your increase injector size, you need to increase fuel pump size too. If you don't the larger injectors will run out of fuel pressure. The minimum recommended fuel pump size would be a 155 LPH unit which is good for 440 naturally aspirated HP. You can go larger if you want to, the excess is returned to the tank.

If you choose larger injectors, you will need a matching calibrated MAF or a custom tune. I recommend PMAS MAFs. See HOME - they are rebuilding their website as of 30-Sep-2010, so you may not find all the information you would like to have.

I would also recommend that you plan on installing a adjustable fuel pressure regulator with the new pump. It will help you tune the system. I recommend Kirban fuel pressure regulators. See Kirban Performance
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info 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

The 24 LB injectors would probably be your best bet. Don't forget that with bigger injectors you will need an aftermarket MAF calibrated to match them or a custom tune.

Put the PRO'm mass air in and the 30's then head to a tuner an get a tune on that thing. My tuner said he's never seen an aftermarket mass air that didn't need to be tweaked to get the tune right. If your not in the twelves with that set up there's something wrong!

MAC'n89Blckstng said:

Put the PRO'm mass air in and the 30's then head to a tuner an get a tune on that thing. My tuner said he's never seen an aftermarket mass air that didn't need to be tweaked to get the tune right. If your not in the twelves with that set up there's something wrong!

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i agree, if u have the extra money to throw into the tune.

My car has gt40's an a e cam and I'm running 30's and it has a really really nice tune. 12.3-12.6 across the board. I'm picking up my car from my tuner's tonight and I'm pumped to see the difference!