Tune MAF/VE Question

Just learning, first post here.

This is for a 2006 Mustang GT with a Rousch m91 supercharger/intercooler. 1/4 mile usage. Car runs fantastic, it has a tune to slow it down to run in the 12.90 class.

Every once in awhile the car during a race day will run slower fro no apparent reason, low 13's, with same 60 ft times. We have been blaming this on the density altitude, which we keep track of on each run. But, now that I am attempting to be more factual about modern car EFI and tunes, this doesn't seem like it can be the case. My thought process is this. This is a MAF based system, which means the signal from the MAF includes effects of any temperature or density changes, i.e. it is measuring the actual mass of air prior to SC. So, this car should not be affected by changes in DA. Correct?

Second concept I'm unsure of. He's making the pass at WOT, which means an open loop status. Are the numbers in this table set or is this table a "learned" set of figures? It seems if we re-flash the tune in between rounds, that the car will run the number and be more consistent. Is this correct?

Thank you, I'm sure it's more complicated than what I have stated, but appreciate your comments and further points of study. :burnout:

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Originally Posted by mauitom

Just learning, first post here.

This is for a 2006 Mustang GT with a Rousch m91 supercharger/intercooler. 1/4 mile usage. Car runs fantastic, it has a tune to slow it down to run in the 12.90 class.

Every once in awhile the car during a race day will run slower fro no apparent reason, low 13's, with same 60 ft times. We have been blaming this on the density altitude, which we keep track of on each run. But, now that I am attempting to be more factual about modern car EFI and tunes, this doesn't seem like it can be the case. My thought process is this. This is a MAF based system, which means the signal from the MAF includes effects of any temperature or density changes, i.e. it is measuring the actual mass of air prior to SC. So, this car should not be affected by changes in DA. Correct?

Second concept I'm unsure of. He's making the pass at WOT, which means an open loop status. Are the numbers in this table set or is this table a "learned" set of figures? It seems if we re-flash the tune in between rounds, that the car will run the number and be more consistent. Is this correct?

Thank you, I'm sure it's more complicated than what I have stated, but appreciate your comments and further points of study. :burnout:

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The very first step in figuring out what is going on is to datalog it. It may be as simple as the air temp difference between on run and another. The amount of ignition timing may be changing due to that, and that would be enough to cause that much fluctuation in ET/MPH.

If you are bracket racing, I would suggest the tune be setup so that the timing is pretty much fixed, except in the case of extreme temps that may cause damage.

Thank you Eric for your reply. That certainly makes sense. It looks like we should be looking at,

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IAT Spark Advance Correction - Add (Base): This table is used to modify spark advance based on inlet air temperature. It adds to the current spark advance.

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Originally Posted by mauitom

Thank you Eric for your reply. That certainly makes sense. It looks like we should be looking at,

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You are correct..
Alot of bracket racers will disable not only that temp correction, but also the one for ECT. There are also other spark adjustment tables that alot of tuners go ahead and zero out as one of the first steps in building the tune. Ive found that some go and disable all while others dont do as much. But for a bracket car, a race tune with all the modifiers zero'd out (except in extreme temperature ranges) will be more consistent