This webpage called Calculating the Right Fuel Injector (which is taken from the Accel performance fuel injector data sheets - linked below) has the mathematics for selecting a fuel injector based on your hp requirements.
I ran the 2.3L specifications through the magic formulas and used BSFC of 0.45, number of injectors = 4 and a duty cycle of 0.80 for a 100 hp engine. They indicated that I would need a stock 14 lb/hr fuel injector. If I wanted 130 hp from the engine, using the same BSFC and duty cycle, I would need an 18.3 lb/hr flow rating. Obviously, the flow rating of the stock fuel injectors is limiting the amount of hp the engine can produce.
I ran across the Accel performance fuel injector data sheets (pdf - Tech Info button) and they list 3 fuel injectors for the 2.3L Ford engine:
Unfortunately, they don't expand on what they mean by Level 1 and 2 performance. This leads to my research, I've found that you cannot just slap on any old higher output fuel injector and expect it to work. The size of the fuel injector and the mass air flow sensor should be matched together within the limits of the computer's (MCU) programming. If you replace any of the components and they are out of the limits of the MCU's programming, you will end up with a poorly performing engine.
From my research, there should be no problem in upgrading to a 15 lb/hr fuel injector without reprogramming the MCU. Now interestingly with the Accel fuel injector data sheets, it limits the available fuel injector flow rate to a maximum of 17 lb/hr. Why only 17 lb/hr and not higher as in the other engines Level 3 to 9 injectors? (Yes other engines have up to 9 levels of performance injectors!) This leads me to believe that the maximum flow rate that is within the MCU's programming limits is 17 lb/hr without changing any other component.
Level 1 - 15 lb/hr fuel injector sources
15 lb/hr from one of the following 2.3L engines:
This should give you 7% increase in fuel to the engine and hopefully 7% more power! I haven't done this yet but expect about 7 to 10 more hp at WOT (wide open throttle) which I use going up hills (I live next to the Rockies).
Level 2 - 17 lb/hr fuel injector sources
There are no stock Ford products that use the 17 lb/hr fuel injectors, but you can use the same Accel 17 lb/hr fuel injector listed as stock replacements for the following GM products (they are 100% compatible):
With a Stage 2 fuel injector, I would expect 21% better fuel flow over the stock 14 lb/hr fuel injectors. Hopefully, this would translate into a 21% increase in available horsepower or roughly an increase of 21 hp! Unfortunately, that's just wishful thinking...
19 lb/hr Fuel Injector
Most all Ford 5.0 V8s with EFI come with 19 lb/hr fuel injectors and are readily available and inexpensive. I figured that with all the intake and exhaust work that I did, I could use the 19 lb/hr fuel injectors. I picked up a set of 4 for $100 off of ebaymotors.
New Fuel Injector Results
I installed the 19 lb/hr fuel injectors and the results were not immediately as dramatic as I expected. It took about 100 km for the computer to learn the new settings. There is about a 10% increase in hp (10 hp) and lots of acceleration. The truck accelerates better and the bottom end is better at 1500 rpm in all gears. I haven't really tried the top end cause I just don't run the truck up there.
The truck is now much more drivable. I don't have to downshift on hills that I had to downshift from 5th to 4th or 4th to 3rd anymore. Whenever I shift gears, I feel a little kick of power as the new gear engages - this includes when shifting to 5th. I can accelerate in any gear starting at 1200 rpm. Oddly, the engine now idles at 600 rpm where with the stock injectors it was idling at 750 rpm. I'm happy to cruise along at 1800 rpm and can accelerate when the pedal is pushed.
Calibrate the MAF
If you change fuel injectors, you should calibrate the MAF to match the new injector size. Go to the Modifying the MAF page and calibrate your MAF. It is very easy, you just have to drill the MAF sample tube to a slightly larger size.
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