Your Brake Specific Fuel Consumption should be around 0.5, and you don't wanna run more than 80% of the injector duty cycle.
HP*BSFC / (8*0.8) = injector size
For example, with 300 FWHP,
300*0.5 / 6.4 = 23.4#
You can adjust the fuel pressure accordingly:
FLOW = (pressure/41psi)^.5 * injector flow rate
(61psi/41psi)^.5 * 19# = 24#
(but you need to calibrate the MAF or the computer).
These 'calibrated' meters typically reduce the voltage that's sent to the EEC so it seems like
there isn't as much airflow. Consquently, the injector pulse-length is shortened, and you get
proper fuel flow with the larger injector.
This can be an advantage cause the stock 19# MAF calibration will peg the max voltage (4.85V) around
330 HP (~530CFM, which is the maximum the stock TB can flow anyway). At this point, the EEC spits out an error code,
and reverts back to the stock lookup table. If you're running a larger MAF, you could be pulling
substantially more air than what the EEC thinks is possible, causing a serious lean condition.
Consequently, I wouldn't run a larger MAF with a stock 19# calibration... you wanna increase injector
size as well.
A 24# MAF calibration is good for around 415 HP, which should be sufficient for most naturally
aspirated combo's. If you're running forced induction, you'll wanna adjust accordingly. Just don't
forget that superchargers use HP, so the flywheel HP may actually be significantly higher than you think
(depending on it's drag).
Problem. Load calculations also depend on the MAF signal. Since the perceived load is lower,
the EEC now provides too much timing advance. As you go to larger injector calibrations, the
EEC's load perception gets worse. At WOT the EEC-IV reverts back to the stock lookup table, but
the EEC-V uses the load calculation all the time (SERIOUS DETINATION?).
The solution is to calibrate the EEC... not just the MAF. You can have a chip burned, or go for
a user programable EEC-tuner or twEECer.
Mass Airflow Meters:
Thermodynamically, HP ~ CFM / 1.6
So CFM = HP * 1.6,
Theoretically, the stock 606CFM MAF should be good for 380HP. It should be noted that the 1989 mustang did loose about 5-10 HP with the MAF addition... probably due to the abrupt 'steps' along the flowpath.
Similarly, the stock 526CFM TB should be good for 325HP, but it's probably not. A rat-tail file can easily smooth out the air path though (I tried a CNC mill, but it took too long, and I went too far).
The FMS 65mm TB is advertised to flow 10% more than stock... 580 cfm should be good for 360 HP.
As mentioned, the 24# MAF calibration reduces the output voltage, so it's actually good for 415HP (~670CFM). Thus, the stock cobra setup (24#, 70mm MAF) is more than enough for most naturally aspirated combo's.
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