Picking fuel injectors?

I am currently trying to put my engine together and wanted to know a little more about which injectors to use (19lb, 24lb, 30lb, etc...)? I tried doing a search but didn't really find what I needed. This is the first time I have done this so my knowledge on the subject is weak. Here is what I have so far:

1995 351W "roller cam"
Lightning GT40 upper/lower intakes

I still need everything else and was hoping for a little help. I have read the fuel injection columns from Bronco Driver and have checked out the Fordfuelinjection.com site but still don't know what works best (or is working good for most). I plan on purchasing a 89-93 Mustang ECU and RJM harness. As always, any input is greatly appreciated.

I have 24 LB injectors on my 351W (non roller cam) GT 40 Upper and lower, Edelbrock Performer RPM Heads, with a MAF calibrated for 24's and a tweecer to tune the computer. The 351 can take 24LB injectors or bigger easily, but the only down side to changing the injectors is to really get load/timing dialed in correctly you will need to get a chip burnt. It really depends on how you are going to be using the engine. The place where bigger injectors really play a part is at higher RPM's and at WOT, - so it depends on what you want out of the engine. Some guys want to bounce their truck off of 6K redline, and need 42LB injectors. But also take into account if you go with much bigger than 24's you will probably have to start looking at alternative high flow fuel pumps.

Here's some info on choosing the right injector size - also check out the mustang sites like www.corral.net - where there is lots of good info
http://www.injector.com/injectorselection.php

Here is how the whole EFI thing works...
The MAF reads how much air is entering the engine. It is programed to produce a voltage based on the amount of air.
The computer looks at the voltage, since it has the program of the MAF (the "look up table") it reads the voltage and knows how much air is entering the engine. From this it does 2 things. Calculates load (interputed based on what its programming) and air/fuel ratios. Usually you want 14.7:1 air to fuel ratio for normal use, a bit lower under heavy load.
So the computer can calculate how much fuel the engine needs. The same computer is also programmed for how big the injectors are. So the computer can calculate what fraction of a second it needs to keep that specific sized injector open to get the right amount of fuel in the engine.

So the right sized injector... The size that is programmed in the computer is the right size. As noted above, a "chip" can reprogram the computer so it knows if you are running injectors a different size then the original programming. The tuned MAF is a cheap shortcut that halfway addresses the ratio issue while usually screwing up the load (ignition timing).

A stock 351 came with 19's
5.0 HOs came with 19's
A stock 460 big block came with 24's
The '93 Cobra came with 24's (although it was rumored to be a marketing ploy more then actually needed)

If the engine is stock, 19's will probably work just fine.

Sounds good. I want a good motor for "daily driving" and occasional trail use. The only "mods" to the engine will probably be the intakes, headers, etc...(peripheral stuff I guess).

Im running 30s with my 351w, but its not stock. World Products Windsor Sr. heads ported & polished. Edelbrock Performer RPM upper and lower intake. 73mm MAF, 65mm TB. FMS camshaft 214/224 duration.

I was running 19s and the stock MAF while I was waiting for a chip to be burned from SCT and my MAF to be recalibrated. I was hitting the duty cycle of the injectors when I would get into higher revs. Now it runs awesome.

If I was to get a "chip" to allow larger injectors, is this easy to do? Are there many places that do this? Cost? What are the major downsides to going this route? Thanks...

kholding said:

If I was to get a "chip" to allow larger injectors, is this easy to do? Are there many places that do this? Cost? What are the major downsides to going this route? Thanks...

Click to expand...

Yes its easy to do. I just went with SCT and game them the specs on my motor and mods and they built the chip accordingly. I believe it was around $200 but I cant remember anymore. The downside is that it costs money.