What Would Larger Injectors Get Me
- Thread starter meknow63
- Start date
I would recommend 24 lb. injectors with an aftermarket MAF to match.
At this time the stock intake manifold is the choke point or bottleneck. Look for an Explorer intake manifold and the 65 MM throttle body that comes with it.
Fuel injector sizing & injector photos
Revised 26-Dec-2014 to add statement about figures are for flywheel HP and not rear wheel HP
Injector HP ratings: this flywheel HP, not rear wheel HP.
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 at the flywheel.
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
36/.5 = 72, 72 x 8 = 576 HP
42/.5 = 84, 84 x 8 = 672 HP
The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.
19/.5 = 38, 38 x 8 = 304 HP x .85 = 258 HP
24/.5 = 48, 48 x 8 = 384 HP x .85 = 326 HP
30/.5 = 60, 60 x 8 = 480 HP x .85 = 408 HP
36/.5 = 72, 72 x 8 = 576 HP x .85 = 490 HP
42/.5 = 84, 84 x 8 = 672 HP x .85 = 571 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 http://users.erols.com/srweiss/calcpchg.htm 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.
If you did turn up the fuel pressure, you might be able to change the injector duty cycle to get the air/fuel mixture ratio you want since the injectors will have extra fuel delivery capability.
With larger than stock injectors or higher that stock fuel pressure, you will need an aftermarket MAF that matches the injector size. The MAF “lies” to the computer to get a fuel delivery schedule that meets the engine’s needs and isn’t too rich or too lean. The best strategy is an aftermarket MAF and a custom tune to insure the best air/fuel ratio over all the RPM range.
Don't forget to increase the fuel pump size when you increase injector size or significantly increase the fuel pressure
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 http://www.veryuseful.com/mustang/tech/engine/ 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
At this time the stock intake manifold is the choke point or bottleneck. Look for an Explorer intake manifold and the 65 MM throttle body that comes with it.
Fuel injector sizing & injector photos
Revised 26-Dec-2014 to add statement about figures are for flywheel HP and not rear wheel HP
Injector HP ratings: this flywheel HP, not rear wheel HP.
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 at the flywheel.
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
36/.5 = 72, 72 x 8 = 576 HP
42/.5 = 84, 84 x 8 = 672 HP
The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.
19/.5 = 38, 38 x 8 = 304 HP x .85 = 258 HP
24/.5 = 48, 48 x 8 = 384 HP x .85 = 326 HP
30/.5 = 60, 60 x 8 = 480 HP x .85 = 408 HP
36/.5 = 72, 72 x 8 = 576 HP x .85 = 490 HP
42/.5 = 84, 84 x 8 = 672 HP x .85 = 571 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 http://users.erols.com/srweiss/calcpchg.htm 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.
If you did turn up the fuel pressure, you might be able to change the injector duty cycle to get the air/fuel mixture ratio you want since the injectors will have extra fuel delivery capability.
With larger than stock injectors or higher that stock fuel pressure, you will need an aftermarket MAF that matches the injector size. The MAF “lies” to the computer to get a fuel delivery schedule that meets the engine’s needs and isn’t too rich or too lean. The best strategy is an aftermarket MAF and a custom tune to insure the best air/fuel ratio over all the RPM range.
Don't forget to increase the fuel pump size when you increase injector size or significantly increase the fuel pressure
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 http://www.veryuseful.com/mustang/tech/engine/ 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
I would go with 30# and matching MAF. You're probably in between 24 and 30#ers right now but I would error on the high side. Better to have to much injector than not enough. That goes for fuel pump also. Any excess fuel will just be returned to the tank.
mikestang63
SN Certified Technician
Totally agree with jrichker. That stock intake is killing your power. I also agree with a5literman about going right to 30#'ers and a 255lph fuel pump. Then get a chip burned- preferably by a local tuner on a dyno. Avoid Bama tunes at all cost. if you want a good mail order tune, I would look at Chris Johnson at SCT or Willie at Dirty Dirty Racing.
You shouldn't EVER recommend a calibrated MAF on an SN-95 pushrod car. With the way the load scaling is done inside the PCM, calibrated maf's can lead to improper timing and startability / driveability problems. The CORRECT answer, is to use a MAF that supports enough airflow metering for the engine it is being attached to. Then you have the PCM calibrated (tuned) for the components that are run on it.
Thank you for your input, I knew that there were some differences, but not to that extent.
I'd wouldn't got with anything less than 30lb/hr injectors on a 331. The 24's might get you buy as long as you stick with the stock intake and GT40 top end, but if you ever decided to swap out to a better head and intake set up, you'll have those 24's up in the 90-100% duty cycle range before you know it.
I'd skip the calibrated MAF route too. I went with 30's and calibrated Pro-M 80 on my 331 and it's been nothing but a PITA. Currently tuning the car with a Moates Quarterhorse and will never dick with calibrated meters again.
I'd skip the calibrated MAF route too. I went with 30's and calibrated Pro-M 80 on my 331 and it's been nothing but a PITA. Currently tuning the car with a Moates Quarterhorse and will never dick with calibrated meters again.
Thank you all for your input, I have a lot more knowledge to work with now (keep the comments coming as I will still check on this thread for more info). I will start looking for a explorer intake and 30# injectors. Is there a brand of injector that you recommend? Im not sure what year explorer intake to get. What should I look for on my engine to determine the right intake.
Thanks again,
Meknow63
Thanks again,
Meknow63
+1 you will grow out of a cobra style intake fast with a 331.
I have 30s on the shelf FRPP shoot me a pm if interested. Slightly used.
Or if you want brand new I will find the link for a FRPP supplier I used for my 50s
I have 30s on the shelf FRPP shoot me a pm if interested. Slightly used.
Or if you want brand new I will find the link for a FRPP supplier I used for my 50s
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