Q&A / Tech

Mailbag: Mass Airflow Sensor Calibration vs. Fuel Injector Size

You’ve got questions. We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re discussing calibrating MAF sensors for your fuel injector size.

J.S. Franklin, TN

Q: I have a 1994 Mustang GT equipped with a manual transmission. I want to upgrade my mass airflow sensor now that I have a cold air intake kit, but I’ve noticed that MAF sensors seem to be based upon the size of the fuel injectors. Is that accurate? And if I add more horsepower to my car, will I need to increase fuel injector size and, by extension, MAF sensor calibration, too?

A: Yes to both questions. Yes, the MAF sensor should be calibrated for the injector size. And yes, at some point you’ll likely have to increase injector size if you keep adding horsepower. At that point, you’ll also want to match the MAF sensor up to the increased fuel injector size.

The key question for you becomes: When will you have to upgrade your fuel injectors?

Fuel injector size is a function of multiple factors: horsepower level, BSFC (brake-specific fuel consumption), and duty cycle. BSFC is the amount of fuel consumed per unit of power produced; duty cycle is the percent of time the fuel injector is open versus the total time between firing events. Both of these numbers can chance as engine modifications are made and the engine becomes more efficient. However, there are a few rules of thumb you can follow to get a good estimate of ideal fuel injector size. We covered those in this post.

In your case, Ford sent the 1994 GT 5.0L out into the world with 215 horsepower. Using Ford’s duty cycle for the factory injectors, you could be at or near the 225-235 horsepower level before considering a larger injector. Arguably, for somewhere around 280 horsepower through 320 horsepower, a 24-pound injector can be used.

Of course, engine dyno testing is the ideal way to determine BSFC, and the dyno would also allow you to work off of real world horsepower figures so you could dial in the size of your fuel injectors.

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  1. I had a question if i may,i have a 91 Mustang and ill be installing a 347 stroker here in the next few months,its considered a “mild” 347 it has a stage 1 trick flow cam, upper gt40 tubular and gt40 heads, not p but regular gt40s and i have some brand new 30 pounders laying around and i wanted to use those with a calibrated pro m mass air meter.

    Im not interested in doing any tuning,this will be a car ill drive around quite regularly and will not be abused in any way save for the occasional romp once in a while, anyhow would this injector size be overkill or just about a little extra room for maybe improvement later? thank you for your time

    • That size should be ok but “calibrated” MAFs are a bad idea and can cause other issues in the tune like over advanced timing. Tuning with the actual MAF curve, engine size and injector size is the best way to go.

  2. Not true at all. They alter the MAF to allow you to use bigger injectors but it screws up load calculations badly which alters the ignition timing also. The best way is a tuning device like a quarterhorse and put in the correct values for the MAF curve and injector size. That way the load calculations are correct and you don’t end up in a situation where you have too much timing advance.

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