Pro's c and Con's of going with speed density tune
10-29-2011, 12:46 AM
#21
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Measuring the current required to keep a wire hot is still measurrement of the incoming air charge. It takes a certain amount of air to cool the wire to a point where current changes. Its indirect measurement, but its still measurement. Just like using a differential pressure meter with an oriface plate to measure flow. In that case you're measuring pressure drop, which correlates to flow rate. With the maf, the change of resistance in the MAF resistors changes current, which is converted to frequency and correlates to a flow rate. Its done using known values. Yes the O2 sensors trim fuel, but like was said, they can't trim under high load conditions. My argument is not that SD is all together bad, but that it is not as good as a MAF+VE tune because it does not meter the incoming air charge. I'll go back to what I said earlier, if you are not metering the incoming air charge then you are making an educated guess. Metering something idirectly, as the MAF does, is still metering none the less. Having the MAF and the VE tuned correctly will give much smoother transitions between cells in the VE table, thus making the fueling more accurate which will cause your O2 sensors to have to trim less.
10-30-2011, 03:51 PM
#22
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Measuring the current required to keep a wire hot is still measurrement of the incoming air charge. It takes a certain amount of air to cool the wire to a point where current changes. Its indirect measurement, but its still measurement. Just like using a differential pressure meter with an oriface plate to measure flow. In that case you're measuring pressure drop, which correlates to flow rate. With the maf, the change of resistance in the MAF resistors changes current, which is converted to frequency and correlates to a flow rate. Its done using known values. Yes the O2 sensors trim fuel, but like was said, they can't trim under high load conditions. My argument is not that SD is all together bad, but that it is not as good as a MAF+VE tune because it does not meter the incoming air charge. I'll go back to what I said earlier, if you are not metering the incoming air charge then you are making an educated guess. Metering something idirectly, as the MAF does, is still metering none the less. Having the MAF and the VE tuned correctly will give much smoother transitions between cells in the VE table, thus making the fueling more accurate which will cause your O2 sensors to have to trim less.
Last edited by joecar; 10-30-2011 at 03:58 PM.
10-31-2011, 05:13 PM
#23
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But that's irrelevent. Every sensor on the car measures by correlation. It doesn't directly measure anything, all of the variables are converted to an electrical signal that correlates to their values. MAP pressure is measured via a strain guage and the computer correlates the change in resistance to pessure, IAT use an RTD which correlates resistance to temp. So nothing measures directly. My point is with SD you get no measurement of incoming air volume at all. The computer does a calculation as to air charge. With MAF you do measure the incoming air charge. Like I said, not advocating MAF only, but MAF+VE like it was designed to work with.
