maxing out stock 19's? upgrading?

24's will be fine, also I would keep stock MAF

mustangman9812 said:

24's will be fine, also I would keep stock MAF

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Your running the same numbers as a Mach. 24's will do.

24's will do but why not leave room for future upgrades?

The 24 lb injectors should be good till about 330 hp and that is estimated at 85% duty cycle. The 30 lb injectors will be good till 410 on the came scale. Bigger is not always better because you will have some loss of tune ability with the 30 lb around idle because your pulse width will have to be decreased a little more than a third. Just some things to think about. If you are not planning on going much over 330 hp the 24 lb injectors will be nuts on for you.

Calculating Fuel Injector Size
Here is the formula for calculating injector size in pounds per hour:

Injector lbs./hr. = horsepower x BFSC/number of cylinders


BFSC is short for Brake Specific Fuel Consumption, which is the amount of fuel required to produce one horsepower. According to Accel, a BFSC of .45 is a good general figure for normally aspirated engines, and .55 is good for supercharged engines.

Let’s do a calculation for a 400 horsepower, unblown V8 engine:

Injector lbs./hr. = 400 x .45/8
Injector lbs./hr. = 400 x .05625
Injector lbs./hr. = 22.5


While nobody makes a 22.5 lbs./hr. injector, our aftermarket injector size chart shows several 24 lbs/hr. injectors, which would work fine on this engine.

Another thing to keep in mind is fuel pressure, which can affect injector flow. You can compensate for a smaller injector by boosting the fuel pressure. An adjustable fuel pressure regulator is ideal for doing this. With all things being equal, though, it’s best to use the right size injector.

Here are the injector sizes for the most popular Ford performance and truck engines. These engines are the most popular for swapping into early musclecars, street rods, and trucks.
•5.0L passenger (302), port EFI: 14 lbs./hr.
•5.0L HO and truck (302), port EFI: 19 lbs./hr.
•4.6L SOHC (Mustang GT), port EFI: 19 lbs./hr.
•4.6L DOHC (Mustang Cobra), port EFI: 24 lbs./hr.
•5.7L truck (351W), port EFI: 19 lbs./hr.
•7.4L truck (460), port EFI: 28 lbs./hr.


Fuel Pumps
Calculating fuel pump size also involves horsepower and BFSC. The formula is divided into two parts. First, you must calculate the pounds per hour (pph) of fuel your engine will require, as follows:

horsepower x BFSC = pph


Then, you divide the pounds per hour figure by six (one gallon of fuel equals approximately six pounds) to determine gallons per hour:

pph / 6 = gph


Let’s calculate the fuel pump size for our hypothetical 400 horsepower motor using a BFSC of .5:

400 x .5 = 200 pph
200/6 = 33.33 gph


To feed that hungry 400 horsepower engine, you will need a fuel pump that delivers 33 gallons per hour. This formula works for any type of engine, carbureted or fuel injected.

Stock EFI Fuel Pump Ratings
If you are swapping a complete factory EFI engine into an early car or truck, the factory fuel pump used with that engine (or an aftermarket pump of the same rating) will be more than enough to feed it. This chart shows the pump ratings for Ford EFI engines in the vehicles equipped with them.
•Mustang 5.0L HO and 2.3L Turbo: 23 GPH @ 50 psi
•Thunderbird 5.0L and 3.8L Super Coupe: 29 GPH @ 45 psi
•F-series trucks, 4.9L, 5.0L, 5.8L, 7.5L (in-tank pump): 50 GPH @ 70 psi
•F-series trucks, 4.9L, 5.0L, 5.8L, 7.5L (external pump): 36-40 GPH @ 70-95 psi

Your Welcome :>

Welcome Man

well said

Im surprised you're not leaning out a bunch up top. I peak at 92/93% duty on my 19's. What's you A/F again?

Edit: I just looked at your graph, it looks like it is leaning out. I see it reaching 14 almost. Most N/A guys shoot for 12.9-13.1, with heavy mods closer to 12.8. But with your compression and cams you're going to want to be closer to 12.4-12.6. going towards 14 at those rpms is no bueno.

98COBRA281 said:

you mean 330rwhp right?, im not sure how much is still in it, but i dont think i will be over 330, how are 24s only good to 330rwhp, when my 19s are making 310rwhp?

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Calculating with an 85% duty cycle 330 is right for 24lbers with your dyno graph it looks like you are over the 85% DC. 85%DC is a good safety factor for sizing your injectors but its not a set in stone number. Depending on what type of fuel injector you buy there is a limit on the amount of duty cycle you can run and keep your injectors at a linear rate. At the extreme bottom and the tippy top, injector flow is non linear hence the 85% factor.

Refer to me edited post, but yeah, most of the A/F line should be just under the dotted line at that power/compression

CobraRed_96_GT said:

Refer to me edited post, but yeah, most of the A/F line should be just under the dotted line at that power/compression

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Yep, below the dotted line is optimal, you can see that at 5100 you detonate and about 5600 **** gets worse . You really don't want to be above 13.0 at those RPM's.

98COBRA281 said:

yeah, i usually see N/A cars shoot for a 13.0AFR, but my tuner wants to get it about 12.5(thats where the dotted line is)

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Oh, thoght the line was 13. yeah 12.5 would be good, i'm in the 12.4-12.6 range under full throttle on the road.