I'm trying to find the correct size injectors for my car. I am considering 30lb.
The formula requires the known horsepower. I have no idea what the car is putting out. Is there another way to determine the right size or is it more of a hit and miss kinda thing.
My car's info is in my signature.
I had no problem deciding the right size carbs on my older cars, the whole injector thing just blows me away.

Thanks.

 

Well seeing as you dont have any internal mods listed, just headers and cai, I would imagine 30 lb mustang injectors would be perfect. If you plan on upgrading cam and heads later you might consider 36's

 

Without mods your stock injectors are fine. Why did you replace the factory fuel pump?

 

Blown94- Thanks, I tried the formula a few different ways and kept hitting around 30lbs.
Tito- My old pump was going out and the fuel gauge sending unit needed to be replaced, while I had it all apart, I put in the Walboro. I knew I was going need it.

 

A few things to think about, WartHog:
First, you are estimating your horsepower, right?
Second, injuneer (who has a wealth of knowledge on the subject) believes those calculators to be inaccurate. You may wish to post both the hp. estimates you entered and the calculator you used (i.e. a link)
Third, those Ford injectors are rated at 30#. at the pressure Ford is using. IIRC, our LT1s, which use 3 bar or 43 p.s.i., run a higher pressure than the Ford. This has the effect of growing the injector value to something larger than 30#.
Fourth, you will need a tune as soon as the injectors are installed. You cannot drive the car without risking washing down the cylinder walls and possibly inducing engine damage.
Lastly, with a proper tune you can install injectors larger than the optimal size. Basically, you dial back on the fueling in the PCM tables. Doing this allows you to purchase larger than required injectors now. Later, as more mods are done, you can again retune to take advantage of the larger injectors rather than purchasing the optimal size injectors again.
Hope this makes sense. BOL.

 

Hey Koolaid, Good info.
The calculator I used is at http://www.rceng.com/technical.aspx
I used 300hp in the formula. It should be close. I just did a rebuild on the motor and add the headers, CAI and 52mm TB along with the madtuner tune.
I had heard that about the Ford injectors not matching their advertised flow on an LT1.
I knew about the re-tune, I am installing a set of 4:10 gears right now also, so I am sending my computer back to Madtuner for a re-tune.

 

The formula you used from RC Engineering is:

(300HP x 0.50 BSFC) / (8 cyl x .80 DC) = 23.44 #/HR

Stock injectors are programmed in the PCM for 24.9 #/HR. Using the RC Eng formula, they are good for 318.7 flywheel HP.

Seems like you had a problem with the math.

My feeling is that the generic, one-size-fits-all formulas like the one on the RC Engineering site (same as virtually every other site) is VERY conservative. My experieince with the LT1 indicates that you can simply multiply flywheel HP by 0.07 to get the MINIMUM required injector size. That corresponds to a BSFC of 0.476 #/HR/HP and an 85% duty cycle.

Using that basis, the stock injectors are good for 355 HP. You aren't there yet.

That said, using a larger that required injector will not hurt anything, as long as the tuner entered the correct flow constant and offsets. When you fill out the tuner's questionnaire, you have to tell him the type of injectors you are using, the rating of those injectors, and the fuel pressure you are running them at. They know the multiplier for running injectors rated at 2.7 bar (39.15psi) is 1.054 when the injectors are operated at 3.0 bar (43.5psi)