Custom ATS Placement

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
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Re: Custom ATS Placement

Post by Dylan »

If this was my engine it would be going in the a manifold runner as per OEM. And from experience.
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Re: Custom ATS Placement

Post by antus »

The tune can be set up for anything, but the sensor for a hot wire type maf needs to be in the sensor as the air temp at the maf is part of the equation that is used to convert hot wire heat loss in to airflow. So when starting with a MAP type tune, the MAT sensor will typically be in the manifold somewhere and by keeping the location similar the stock values in the tune will be closer making it easier to get more accurate results. As noted air temp does not play a huge factor (except perhaps on turbos) but I would keep it closer to stock where possible.
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Re: Custom ATS Placement

Post by charlay86 »

Ant, I was under the impression that the GM MAF sensors had their own ambient air temp sensors built in to the sensor, as the sensor's control circuitry uses it for the compensation internally before it produces the output signal.
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Re: Custom ATS Placement

Post by antus »

Yes and its fed back to the pcm too. Thays why you need the splitter in the maf loom to wire in another one when you go mafless. Mind you im thinking ls1 maf, v6 delco pcm might be different.
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Re: Custom ATS Placement

Post by MAGP »

charlay86 wrote:Ant, I was under the impression that the GM MAF sensors had their own ambient air temp sensors built in to the sensor, as the sensor's control circuitry uses it for the compensation internally before it produces the output signal.
Not all MAFs have an air temp sensor as such. They have a hot wire that adjusts to suit the flow of air. More airflow requires more power to keep the hotwire at temp, less airflow requires less power to keep the hotwire at temp. The airflow is calculated by how much power is required to keep the hotwire at temp. Modern MAFs have both sensors in the 1 unit but the MAFs used by Holden until the series 2 VT (I don't know much about them after the series 1 VT) didn't have a dedicated air temp sensor like an IAT or MAT.
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Re: Custom ATS Placement

Post by antus »

Right ok. So that makes sense. But that is still why its at the MAF. The air temp at the hot wire makes all the difference to measured air flow (it'll take a lot more 80 degree air to remove the same amount of heat as 5 degree air). Then the air continues to heat as it travels further in the engine bay. So that is what the tune starts at and its simpler to leave it but you dont have to.
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Re: Custom ATS Placement

Post by vlad01 »

Yes that is correct and there is even management systems that take humidity measurements as well to get even higher accuracy as humid air absorbs more heat than dry air does.
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Re: Custom ATS Placement

Post by MAGP »

antus wrote:Right ok. So that makes sense. But that is still why its at the MAF.
Actually that was all about tooling and cost of parts. A plastic clip in sensor is cheaper to produce than a metal screw in sensor. Drill and thread a metal manifold or have a preformed hole in the airbox, what will be cheaper? it was all about cost.
antus wrote:The air temp at the hot wire makes all the difference to measured air flow (it'll take a lot more 80 degree air to remove the same amount of heat as 5 degree air). Then the air continues to heat as it travels further in the engine bay.
That's all correct
antus wrote:So that is what the tune starts at and its simpler to leave it but you dont have to.
I think you are mixing up the sensors here. The MAF sensor has the hotwire, the air temp sensor is a resistor. The air temp sensor merely calculates the temp of the air based on resistance like a coolant sensor does. Air at a MAF is going to be cooler than air at the manifold to head surface after the engine has been running for a couple of minutes. Having the air temp read near the inlet valve provides a more accurate measurement of real world conditions.
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Re: Custom ATS Placement

Post by vlad01 »

Ants point is the ECU needs to know the condition of the air before entering the MAF so that it can accurately calculate and compensate metered based on atmospheric conditions that effect the MAF readings.

Its a lot more accurate, easier and faster to calculate knowing before rather than trying to work backwards and fish out information when a heap of other influences have mixed in already effecting temp readout.

its like trying to work out a crime scene verses having witnesses standing around observing before it happens. I know which would be a lot easier to figure out.
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Re: Custom ATS Placement

Post by MAGP »

vlad01 wrote:Ants point is the ECU needs to know the condition of the air before entering the MAF so that it can accurately calculate and compensate metered based on atmospheric conditions that effect the MAF readings.
My point is it doesn't. No ECU needs to know what the atmospheric conditions are, all they need to know how much air is entering and what temperature it is. Where the temp is taken is neither here nor there because mathematical equations do the calculations but the mathematical equation is much more complex when air temp is taken without factoring in increases in temp because of engine heat. The amount of fuel required is based on air density and how much air in ingested. If you have an air temp sensor before the MAF the air temp is not going to be the same in the engine near the valve and therefore air density will not be the same. Change the thermostat to one cooler or hotter than the OEM temp and you throw the equations out of the window and everything is just a gues because an engine running at 160 degree has different fuel requirements to one running at 195 degrees. This is because the diference in temp changes the density of the air mass. If you measure air temp outside of the engine you need to add more to the equation to adjust for air temp and that doesn't take into account fluctuations within the cooling system.
vlad01 wrote:Its a lot more accurate, easier and faster to calculate knowing before rather than trying to work backwards and fish out information when a heap of other influences have mixed in already effecting temp readout.
It cannot possibly be more accurate because of the reasons explained in the last paragraph. It is a fudge at best because at any one time the ECU cannot compensate for an increase in air temp at the inlet valve or injection point. Measuring air temp at the injection point is a real world measurement, measuring 12" or so away and using a mathematical equation that doesn't take into account spikes in engine temp and how it affects air density is a fudge.
vlad01 wrote:its like trying to work out a crime scene verses having witnesses standing around observing before it happens. I know which would be a lot easier to figure out.
Methinks your analogy is a bit back to front. You think figuring out air temp at the injection point with a sensor right there is more difficult than figuring out air temp with a sensor 12" away?
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