Cam Change with MAF Calibration

[1slowbusa]

Question came up this afternoon between me and a co-worker. When taking a stock LS1 engine and installing a bigger cam (just say G5X3), does the MAF airflow vs. output frequency have to be recalibrated?
It makes sense to me that it would need recalibrated because of the bigger duration of the cam will allow more air movement thru the MAF as compared to a stock engine at the same RPM? Or does the maf airflow vs. output frequency only need modified if a bigger MAF is installed?
Thanks,

[eficalibrator]

If you change only the cam (leave the airbox completely stock from filter to throttle body), then there should be no reason to update the MAF transfer in the tune. However, the pumping efficiency WILL be different. You should recalibrate the VE surface(s) since this plays a large role in airflow estimates, especially at low speed.

Many people change "just the lid" prior to installing a new camshaft and neglect recalibrating the MAF curve then. If this is the case, then whatever error you previously had will only get magnified when you add VE error from the new cam as well.

Greg Banish
Calibrated Success, Inc.

[1slowbusa]

If you change only the cam (leave the airbox completely stock from filter to throttle body), then there should be no reason to update the MAF transfer in the tune. However, the pumping efficiency WILL be different. You should recalibrate the VE surface(s) since this plays a large role in airflow estimates, especially at low speed.

Many people change "just the lid" prior to installing a new camshaft and neglect recalibrating the MAF curve then. If this is the case, then whatever error you previously had will only get magnified when you add VE error from the new cam as well.

Greg Banish
Calibrated Success, Inc.

Thanks,
I have read many tuning and performance books but i have not found one on how to recalibrate the MAF. Is there a book that you know of or do you have the procedure?

[pajeff02]

Calibrating the MAF is accomplished by disabling certain engine sensors and tables in the tuning file that affect the air/fuel ratio. Once these are disabled, readings are taken of the vehicle's actual air/fuel ratio with a wideband under steady state conditions. The difference between measured air/fuel and stoich provides the adjustment value needed to correct the MAF's output. The MAF tables are then adjusted accordingly before everything is returned to normal. Unfortunately, I can't give you a step-by-step on this at the moment.

[1slowbusa]

Calibrating the MAF is accomplished by disabling certain engine sensors and tables in the tuning file that affect the air/fuel ratio. Once these are disabled, readings are taken of the vehicle's actual air/fuel ratio with a wideband under steady state conditions. The difference between measured air/fuel and stoich provides the adjustment value needed to correct the MAF's output. The MAF tables are then adjusted accordingly before everything is returned to normal. Unfortunately, I can't give you a step-by-step on this at the moment.

Does recalibration of the MAF have to be done on a Dyno?

[pajeff02]

Does recalibration of the MAF have to be done on a Dyno?

You can do it on the street but it is more difficult. A load bearing dyno allows you to hold the engine at a steady rpm and load in order to obtain accurate readings. You can check out Banish's video to see tuning performed on a dyno. The same principles apply to what you need to do.

[0rion]

Thanks,
I have read many tuning and performance books but i have not found one on how to recalibrate the MAF. Is there a book that you know of or do you have the procedure?

what are you using to tune with? Are you also using a wideband?

[Frost]

If you change only the cam (leave the airbox completely stock from filter to throttle body), then there should be no reason to update the MAF transfer in the tune. ....

Hey Greg,

The OEM MAF table is seriously lower than actual everywhere above 7-ish KHz and it gets worse as frequency rises though. The newer cars have curves that are closer to real life, but not these 98-02 F-bodies. An easy illustration for the un-initiated... Take a stock car (stock lid and air intake) and turn off COT and set PE, for example, to 12.0:1 AFR / 0.82 λ. Log a run and see; the car will be leaner than 13:1 AFR / 0.89 λ on that 12:1 commanded.

I know your post is more of a generalization made to underscore that assuming the MAF was already good, if none of it's ducting changed, it shouldn't have to either. I'm not trying to correct you, just to point out that in this specific application, the OEM curve itself is in fact, no good

[eficalibrator]

Good point, Steve. You're absolutely right that my post was a generalization meant to point people in the right direction. Modern practice is that the OEM derives the MAF transfer function on a flow bench off the vehicle where they flow everything from the filter to the throttle body and just get the data they're looking for. In the aftermarket, we typically use the engine as our flow bench and correct based on lambda errors. There are still the occasional exceptions that prove the rule, so it's always a good idea to verify as you suggested.

Greg Banish
Calibrated Success, Inc.

[1slowbusa]

what are you using to tune with? Are you also using a wideband?

Tuning with HP Tuners and yes using a wide band.

[LSXZ28]

Every car I tune gets the VE tuned first with the MAF out of the equation (Speed Density) and then the MAF table is tuned after the VE is correct... the only way I trust that each table is correct is to tune it... as Steve said above, I have found many of the OEM curves to be off.

[1slowbusa]

Thanks to all.

[Tampa Tuning]

Every car I tune gets the VE tuned first with the MAF out of the equation (Speed Density) and then the MAF table is tuned after the VE is correct....

Me to, but I scale in the injectors first if they have been changed