ok wow so been doing some reading and looks like if i had the maf calibrated to its size and injector size i probably get away with stock ecm for a bit till i could get it in to really tweek it.also 24lbs injectors i would say would be fine for the hp our motors put out even with FI,i would think anything over 30lb would just be too much.also anyone that is running a larger maf on there 4.0 should get a new sample tube for sure.im going to email them and get a tube for my 70mm maf and 30lb injectors.good read
http://www.cnlperformance.com/MAF_info3.html
Let's use another example. This time for 30lb injectors on the same 1989-1993 Mustang 5.0:
19lb calibration vs 30lb
As you can see in this example, the 30lb injector calibration is much higher "vertically" on the graph, as it requires a higher level of airflow to achieve the same voltage output. In this particular application, a 76mm upgrade MAF housing with a "Purple" coded calibration tube is utilized with a conical filter mounted directly on the end of the MAF housing. This calibration requires 57.16% more airflow to achieve the 4.6 volt data point (as highlighted by the green vertical line) versus the "optimized" 19lb calibration. This calibration is almost "perfect", as when you divide 30 by 19, the result defines that the MAF calibration must require 57.8% more airflow to achieve the same air/fuel ratio as the optimized 19lb calibration does with the factory stock injectors. This means that your air/fuel ratio at 4.6 volts with 30lb fuel injectors will be within ONE PERCENT of the air/fuel ratio that is realized with the "optimized" 19lb calibration and factory 19lb fuel injectors.
Since your factory computer processor (without any custom tuning) still contains definitions for 19lb injectors and the stock factory mass airflow assembly (in the transfer function table), this is how ALL aftermarket mass airflow units are able to compensate for larger than stock injectors while still running the factory computer processor. Whether you use our calibration tube method, or if you have a unit that features a modified factory sensor, this is how you are able to upgrade the injector size without changing the computer programming. This is the way that it has ALWAYS been done, and this is the only way that the aftermarket has ever compensated for larger than stock fuel injectors with a factory stock processor in the Ford performance aftermarket. Even if you purchase a unit from another company that features a modified sensor, this is still what is taking place and is the method that is used to achieve a proper air/fuel ratio with larger fuel injectors and factory computer programming.
It is our belief that although the method of sending a re-calibrated MAF signal to the computer to adjust for larger injectors with the factory computer is tried-and-true, it does have its limitations. We believe that a re-calibrated MAF signal when used with a factory stock computer should only be utilized for up to 42lb injectors on vehicles that originally came equipped with 19lb or 24lb fuel injectors. As the injector size is increased, the MAF voltage output must be decreased at a given airflow rate. You reach a point at which the voltage must be reduced so much that it affects the quality of the signal at low airflow ranges such as idle. Once the voltage level goes below .5 volts it becomes very unstable (as mentioned before) because the sensor is most sensitive at low airflow rates and becomes less sensitive as the airflow rate increases and the signal output approaches 5 volts. This can be seen in all of the transfer function graphs provided on this page, as the graph ramps "upward" at an increasing rate as the output approaches the 5 volt level. As the injector size is increased, the MAF voltage output must continuously be lowered. All the while your computer processor STILL BELIEVES that you are running 19lb injectors and a factory stock mass airflow unit/calibration.
At a certain point, you are expecting far too much from the factory stock computer. When running large fuel injectors with custom tuning, you are able to re-define both the injectors installed with the ACTUAL injector slope values, as well as the corresponding MAF table for the ACTUAL mass airflow calibration that you are running on the vehicle. The result is a configuration that duplicates the programming and physical configuration that Ford would have utilized had your vehicle come from the factory with your same aftermarket MAF unit and installed fuel injectors. This results in a superior tune, and allows for high levels of power with the best drivability possible for your combination.
Although a lot of custom tuners do this by retrofitting newer MAF units (like the 2001-2004 Lightning or 2003-2004 Cobra assemblies) to older vehicle applications, the total "range" of these units will not support high levels of power, as their voltage output will exceed 4.99 volts at less than 500 rear wheel horsepower. This goes back to the fact that Ford chose the calibration for these applications based upon the maximum horsepower of the original application, with a certain amount of additional range to facilitate some typical modifications that would be performed to the vehicle (boost pulley upgrades, etc.) which would increase the MAF voltage output. In order to facilitate the needs of high horsepower 1989 to 2001 applications where large injectors and custom tuning is utilized, we have developed specific direct fit units that utilize a patented calibration method which provides the adequate range to meet or exceed the voltage range requirements of such applications. This will be expanded upon further in section 6: "Tuner Calibrations and Computer Tuning" .
Fuel Injector Size Considerations:
If you run a fuel injector that is much larger than what is needed for your application, then this will result in the computer processor not properly calculating load. This can lead to the computer delivering the wrong level of timing to the engine at various conditions, including wide open throttle. With the proper sized injector for your particular combination, your voltage output in a naturally aspirated arrangement will typically max out somewhere between 4.6 to 4.7 volts at wide open throttle at your maximum RPM level. The use of a "ram air" type system is not recommended, as it can cause the voltage value to become too high as a result of the sensor being exposed to (reading and reporting) more airflow to the computer than the engine is actually processing. This will be explained in detail in section 4: "How various factors affect a MAF calibration/signal" .
As a general rule, it takes .5 (or ½) pound of fuel per hour to generate one horsepower in a naturally aspirated application at a standard rated fuel pressure rate of 42 to 43 psi (roughly 3 times atmospheric pressure). To estimate your proper injector size, you can use the following formula:
Maximum Horsepower Estimate Divided by 2 (for ½ pound of fuel per hour to generate one HP) Divided by 8 (for number of injectors).
Using this formula, we will calculate the appropriate injector size for a 345 HP rated "crate engine" as: 345/2/8= 21.56 lb/hr. This means that a 24lb injector is more than capable of supporting the fuel requirements of a 345HP engine with 8 fuel injectors at a standard fuel pressure level at wide open throttle. If it were a 6 cylinder engine, the injectors would need to be larger (345/2/6 = 28.75 lb/hr) because there are two less fuel injectors available to deliver fuel. In such an application, a 30lb injector would be sufficient. For a V8 application, the following common injector sizes support up to the following horsepower levels:
19lb/hr: 304 HP
24lb/hr: 384 HP
30lb/hr: 480 HP
36lb/hr: 576 HP
42lb/hr: 640 HP*
*The most commonly utilized 42lb/hr injectors have an ACTUAL flow rate of 40lb/hr.
Since Supercharged or Turbocharged applications require a slightly richer air/fuel ratio, they need approximately 10% more fuel capacity than naturally aspirated applications. To estimate the HP capacity for each of the above injectors sizes in a forced induction application at a standard fuel pressure level (not using an FMU device), multiply the HP values by .9 to compensate for the additional fuel required.
Elevated fuel pressure levels will increase the maximum flow rate of the injector. The effects of this can be calculated as follows:
Raised Fuel Pressure Divided by Injector Rated fuel pressure equals percent difference of fuel pressure. Take the square root of this value and multiply it by the Rated Injector Size.
For example, if we take a 24lb rated fuel injector and run an FMU (fuel management unit) that elevates the fuel pressure under boost conditions to 65 psi, you would calculate the effective fuel injector flow rate by taking the maximum fuel pressure (65 psi) divided by the injector's rated fuel pressure (43 psi) to get a factor of 1.5116. You then take the square root of this number (1.2294) and multiply it with the original rated injector value of 24lb to get 29.507 lb/hr. This means that when the fuel pressure level on a set of 24lb rated fuel injectors reaches 65 psi, the effective flow rate (due to the increased pressure) becomes close to that of a 30 lb/hr injector at the standard 42-43 psi. This formula is universal, and can be used to calculate the flow rate changes for fuel injectors when adjustments are made with an adjustable fuel pressure regulator as well.
might just wing it and go with a 76mm with 36lbs tbird maf
