24lb injectors question

[Takis31gk]

So I've got 24lb injectors in my 302, but recently changed my old MAF sensor after after the car was tuned by Dez Racing because at a certain RPM it would go haywire and replaced it with another stock one (I believe stock MAF sensors are paired with 19lb injectors). Should I go with a 93 Cobra MAF sensor because I know they used 24lb injectors on those motors, or should I have the new sensor calibrated?

 

[FISHTAIL]

So I've got 24lb injectors in my 302, but recently changed my old MAF sensor after after the car was tuned by Dez Racing because at a certain RPM it would go haywire and replaced it with another stock one (I believe stock MAF sensors are paired with 19lb injectors). Should I go with a 93 Cobra MAF sensor because I know they used 24lb injectors on those motors, or should I have the new sensor calibrated?

It doesn't work like you think. MAF sensor's aren't paired with anything, they just report different voltages as different amounts of air flow by the element. When placed into a particular housing, the amount of airflow represented by a given voltage can be known, and a transfer function is generated. It's from this transfer function that the computer can begin to calculate the injector pulse width at any given point (other factors come into play as well, including feedback from O2 sensors, IAT's, engine load, battery voltage, etc).

The whole "calibrated" MAF myth was started by the aftermarket companies that wanted to sell meters to folks that didn't want to pay for a tune. There are some good writeups on how this was done, but basically it's resulted in years of confusion for folks. The main point to take away from it all is meters are not calibrated to anything. They have a transfer function, and that's it.

That said, you can't use a 93 cobra MAF in your car without a re-tune. The transfer function is very different from stock, and the car won't run. Some other meter types work (like 94/95GT meters) because the transfer functions are sufficiently close to the stock one that the car can run.

If the car started acting funny at a certain RPM after a retune it's probably because they messed something up in the tune, not because you have a bad meter. A bad meter would likely not act up only at paticular RPM's, it sounds more like they have something screwy in your load/fueling tables, or they messed up the transfer function somewhere.

 

[Takis31gk]

It doesn't work like you think. MAF sensor's aren't paired with anything, they just report different voltages as different amounts of air flow by the element. When placed into a particular housing, the amount of airflow represented by a given voltage can be known, and a transfer function is generated. It's from this transfer function that the computer can begin to calculate the injector pulse width at any given point (other factors come into play as well, including feedback from O2 sensors, IAT's, engine load, battery voltage, etc).

The whole "calibrated" MAF myth was started by the aftermarket companies that wanted to sell meters to folks that didn't want to pay for a tune. There are some good writeups on how this was done, but basically it's resulted in years of confusion for folks. The main point to take away from it all is meters are not calibrated to anything. They have a transfer function, and that's it.

That said, you can't use a 93 cobra MAF in your car without a re-tune. The transfer function is very different from stock, and the car won't run. Some other meter types work (like 94/95GT meters) because the transfer functions are sufficiently close to the stock one that the car can run.

If the car started acting funny at a certain RPM after a retune it's probably because they messed something up in the tune, not because you have a bad meter. A bad meter would likely not act up only at paticular RPM's, it sounds more like they have something screwy in your load/fueling tables, or they messed up the transfer function somewhere.

That makes sense, Thanks! On the dyno, when you'd hit 4500RPM or so the air/fuel reading would be a bit erratic so tuners suggested I change out the MAF sensor, which was no big deal and I replaced the air filter as well because it was old and dirty. I just wasn't sure if I could have gone with the Cobra one. The car runs fine now so I'm not worried, just curious.

 

[FISHTAIL]

That makes sense, Thanks! On the dyno, when you'd hit 4500RPM or so the air/fuel reading would be a bit erratic so tuners suggested I change out the MAF sensor, which was no big deal and I replaced the air filter as well because it was old and dirty. I just wasn't sure if I could have gone with the Cobra one. The car runs fine now so I'm not worried, just curious.

Ahhh, now I understand. Yes, that can happen, especially if you have a CAI with a sharp bend right in front of the meter. You can end up with ratty samples at various RPM. I had serious problems with this using a C&L, and to rectify it I went with a 90mm LMAF and an Anderson Motorsports intake.

You could use the cobra meter if you wanted, but you'd need a retune to do so. You'd be better off going with 94/95 meter if you were going to do that, as they are larger anyway. Additionally, if your going to pay for a retune, I'd just go ahead and get something big enough to accommodate you as you continue to mod so you aren't constantly changing meters out. Something like the 90mm LMAF or a slot meter.