What size injectors ?

[ffemt1121]

I have a 88 mustang gt with a 302 . I just bought a holley systemax upper and lower intake. Im trying to find a set of gt-40 heads to port and match the intakes. I plan on using a tfs stage 1 cam. With all that in mind, what size injectors should I get. Some people tell me 24lb. others tell me 30 lb. I plan on running 12's on the motor and any help would be appreciated. Also, is there in difference in power between a 65mm and a 75mm tb with spacer ?

 

[84Ttop]

24lb injectors w/ a matching meter should be fine for this combo, with a good fuel pump of course. Do you plan on any type of power adder later down the road?

 

[earleys94gt]

24's will get you by, but you could also get some 30's or 36's in advance for future mods.

 

[84Ttop]

24's will get you by, but you could also get some 30's or 36's in advance for future mods.

Depending soley on what type of future mods. A boosted app, no but a small amount of nitrous yes, remember w/ a wet kit you are introducing more fuel w/ the nitrous. And there is such a thing as too much injector. You car will run and idle poorly if the injector duty cylce is too low at idle or part throttle.

 

[ffemt1121]

No power adder lately.

People tell me that anything more than 30 would require tuning with my computer. There isnt an idea yet on a power adder but you never know. A 255lph fuel pump is in the future. Also has there been problems with mix-matching parts such as tfs stage 1 cam with a holley upper and lower and gt-40 heads ? People have told me problems but to just make sure the rpm ranges match.

 

[84Ttop]

People tell me that anything more than 30 would require tuning with my computer. There isnt an idea yet on a power adder but you never know. A 255lph fuel pump is in the future. Also has there been problems with mix-matching parts such as tfs stage 1 cam with a holley upper and lower and gt-40 heads ? People have told me problems but to just make sure the rpm ranges match.

That combo seems reasonable. A bigger fuel pump is a must! Most cars that we do that have bigger than 30lb injectors have power adders and are all custom tuned.

 

[Cobra912]

I had 30's on my 331 without a tune and ran great. I upgraded to a blower so I swapped them out for 42's and therefore tuning was required. I would go with 30's, you'll have enough fuel for any N/A combo.

 

[jrichker]

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

 

[Manewaymja2]

I run 24lb injectors with calibrated MAF and i spray a 200shot (wet kit) all day long with 7 degrees retard, no problems and car isnt tuned yet.

 

[SMOKEDYA]

24's will get you by, but you could also get some 30's or 36's in advance for future mods.

is that your car in your avatar? post a bigger pic of it. national trails? peace










john

 

[Cobra912]

I knew jrichker would chime in, that's the info you need.