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sd101 [2009/06/15 10:09]
dmertz
sd101 [2024/03/15 11:16] (current)
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 In calculating fuel requirements for an engine, the amount of air (n in the above equation) is the critical piece of data we need to solve for.  To solve for that, we need to know absolute pressure, absolute temperature and volume. In calculating fuel requirements for an engine, the amount of air (n in the above equation) is the critical piece of data we need to solve for.  To solve for that, we need to know absolute pressure, absolute temperature and volume.
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 ===== Pressure and Temperature ===== ===== Pressure and Temperature =====
-Pressure and temperature are easy enough to measure in our application using off the shelf sensors like the GM IAT and/or the GM 3-bar sensor. ​ Other pressure sensor options are listed on our [[externalsensorlist|Aftermarket Sensor List]]. ​ These include the GM 3.3-bar, AEM 3.5-bar and AEM 5-bar sensors. ​ Other sensors listed on that page can be logged, but are not suitable for SD operation because they do not provide a reliable **absolute** pressure reading.+Pressure and temperature are easy enough to measure in our application using off the shelf sensors like the GM IAT for temperature ​and the [[https://​www.ecmtuning.com/​product_info.php?​cPath=28&​products_id=47|4-bar sensor]] we provide on our site for pressure.  Other pressure sensor options are listed on our [[externalsensorlist|Aftermarket Sensor List]]. ​ These include the GM 3-bar, ​GM 3.3-bar, AEM 3.5-bar and AEM 5-bar sensors. ​ Other sensors listed on that page can be logged, but are not suitable for SD operation because they do not provide a reliable **absolute** pressure reading.  We also offer a [[https://​www.ecmtuning.com/​product_info.php?​cPath=28&​products_id=50|Speed Density bundle]] on our site as well, which includes the standard 4-bar pressure sensor and the IAT sensor along with necessary pigtails and bung.
  
 For air temperature,​ the only supported sensor is the GM IAT sensor (AEM IAT sensor is actually the same thing). ​ You can get part number information off the [[externalsensorlist|Aftermarket Sensor List]] page.  ​ For air temperature,​ the only supported sensor is the GM IAT sensor (AEM IAT sensor is actually the same thing). ​ You can get part number information off the [[externalsensorlist|Aftermarket Sensor List]] page.  ​
  
-When you connect these sensors to your ECU, note that you must connect the GM IAT sensor to the IAT input on the ECU.  There is no other supported IAT input. ​ For the pressure sensor, you can log that on any available (and compatible) input on the ECU.  ​+When you connect these sensors to your ECU, note that you must connect the GM IAT sensor to the IAT input on the ECU.  There is no other supported IAT input. ​ For the pressure sensor, you can log that on any [[externalsensorinput|available (and compatible) input]] on the ECU.  ​
  
 Accuracy is important, particularly for the pressure readings. ​ [[sdhose|The MAP sensor should be connected as intimately as practical to the intake manifold.]] ​ Long, narrow hoses and tee fittings in the path to the sensor slow the response of the pressure sensor, resulting in poor airflow determination. ​ The delayed pressure response will result in poor throttle response and poor control over air/fuel ratio whenever the intake manifold pressure changes. ​ Since both sensors are referenced to the ECU's sensor ground circuit, it's also important that the ECU's sensor ground circuit isn't disrupted by having high-current devices attached to sensor ground. Accuracy is important, particularly for the pressure readings. ​ [[sdhose|The MAP sensor should be connected as intimately as practical to the intake manifold.]] ​ Long, narrow hoses and tee fittings in the path to the sensor slow the response of the pressure sensor, resulting in poor airflow determination. ​ The delayed pressure response will result in poor throttle response and poor control over air/fuel ratio whenever the intake manifold pressure changes. ​ Since both sensors are referenced to the ECU's sensor ground circuit, it's also important that the ECU's sensor ground circuit isn't disrupted by having high-current devices attached to sensor ground.
  
 As normally installed, MAF translators do get their ground from ECU sensor ground via the Mitsubishi MAF connector and do draw a moderate amount of current, particularly when powering the GM MAF sensor at higher airflow, so expect the pressure and temperature readings to change a little when you unplug the MAF translator. ​ Changing the translator'​s ground from ECU sensor ground to chassis ground instead will eliminate this effect. ​ Cut the MAF translator'​s ground wire between the translator box and the Mitsubishi MAF connector and connect the end of this wire coming from the translator to chassis ground. ​ Leave the wire end that remains on the translators Mitsubishi MAF connector isolated and insulated. As normally installed, MAF translators do get their ground from ECU sensor ground via the Mitsubishi MAF connector and do draw a moderate amount of current, particularly when powering the GM MAF sensor at higher airflow, so expect the pressure and temperature readings to change a little when you unplug the MAF translator. ​ Changing the translator'​s ground from ECU sensor ground to chassis ground instead will eliminate this effect. ​ Cut the MAF translator'​s ground wire between the translator box and the Mitsubishi MAF connector and connect the end of this wire coming from the translator to chassis ground. ​ Leave the wire end that remains on the translators Mitsubishi MAF connector isolated and insulated.
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 ===== Volume ===== ===== Volume =====
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 Volume = displacement * VE[rpm, pressure] Volume = displacement * VE[rpm, pressure]
  
-If the VE for an engine running speed density is larger than the true VE of that engine at any given point, then the resulting airflow calculation will be higher than it should be and the resulting A/F mixture will be richer than intended as well.  So you can see that getting the VE table defined accurately is one of the more critical (and variable) pieces to smooth speed density operation.+If the VE table lookup ​for an engine running speed density is larger than the true VE of that engine at any given point, then the resulting airflow calculation will be higher than it should be and the resulting A/F mixture will be richer than intended as well (because the ECU will inject more fuel than is required because it's assuming there'​s more airflow going in than there really is).  So you can see that getting the VE table defined accurately is one of the more critical (and variable) pieces to smooth speed density operation.
  
  
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 A typical SD VE table might look something like the following (click to enlarge). A typical SD VE table might look something like the following (click to enlarge).
  
-{{  ​http://​www.ecmtuning.com/​images/​forums/​sddata/​sdtable.png?​446x244 ​ }}+{{  ​https://​www.ecmtuning.com/​images/​forums/​sddata/​sdtable.png?​446x244 ​ }}
  
 It may seem intimidating at first, but it's really not as bad as it looks. ​ We provide a number of tools and helpers to make dialing the VE table in on your own car pretty easy.  And, honestly, most people may find that they can just drop the "​stock"​ VE table we provide into their car and basically fire it up and drive around. ​ There'​s no doubt some amount of dial-in will be necessary, of course. ​ But for basic driveability,​ it should work fine. It may seem intimidating at first, but it's really not as bad as it looks. ​ We provide a number of tools and helpers to make dialing the VE table in on your own car pretty easy.  And, honestly, most people may find that they can just drop the "​stock"​ VE table we provide into their car and basically fire it up and drive around. ​ There'​s no doubt some amount of dial-in will be necessary, of course. ​ But for basic driveability,​ it should work fine.
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-====== ​Emperical ​Results - Temperature ======+ 
 +====== ​Empirical ​Results - Temperature ======
 The above discussion was all about the theory behind speed density operation based solely on air properties by themselves. ​ But the reality is that air temperature is also affected by engine temperature. ​ As air is entering the engine, it's heated by the temperature of the engine itself. ​ This effect is more pronounced with slower moving air (idle/​cruise) and gradually reduces in impact as airflow rate increases. The above discussion was all about the theory behind speed density operation based solely on air properties by themselves. ​ But the reality is that air temperature is also affected by engine temperature. ​ As air is entering the engine, it's heated by the temperature of the engine itself. ​ This effect is more pronounced with slower moving air (idle/​cruise) and gradually reduces in impact as airflow rate increases.
  
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 Because we know this concept may be not be mainstream, we offer the following datalogs that have *no* air temperature compensation. ​ All the temperature compensation in both these logs is based on coolant temperature. Because we know this concept may be not be mainstream, we offer the following datalogs that have *no* air temperature compensation. ​ All the temperature compensation in both these logs is based on coolant temperature.
  
-[[http://​www.ecmtuning.com/​images/​forums/​sddata/​hotidle-noiat.elg|Hot idle - no IAT]] \\  +[[https://​www.ecmtuning.com/​images/​forums/​sddata/​hotidle-noiat.elg|Hot idle - no IAT]] \\  
-[[http://​www.ecmtuning.com/​images/​forums/​sddata/​coolidle-noiat.elg|Cool idle - no IAT]]+[[https://​www.ecmtuning.com/​images/​forums/​sddata/​coolidle-noiat.elg|Cool idle - no IAT]]
  
 These were captured minutes apart from each other on the exact same car idling in the exact same spot in our parking lot.  In one, air temperature varies from 172F to 130F while in the other it's only 70F the whole time. These were captured minutes apart from each other on the exact same car idling in the exact same spot in our parking lot.  In one, air temperature varies from 172F to 130F while in the other it's only 70F the whole time.
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 However, at wide open throttle, the air temperature seen by the IAT sensor quickly takes over as the primary factor in determining air density. ​ We have logs showing this effect as well with measured A/F ratio dipping to 8.3:1 with IAT at 133F compared to A/F ratio of 9.1:1 at 65F with boost around 20psi. ​ These logs can be found below. However, at wide open throttle, the air temperature seen by the IAT sensor quickly takes over as the primary factor in determining air density. ​ We have logs showing this effect as well with measured A/F ratio dipping to 8.3:1 with IAT at 133F compared to A/F ratio of 9.1:1 at 65F with boost around 20psi. ​ These logs can be found below.
  
-[[http://​www.ecmtuning.com/​images/​forums/​sddata/​coolwot-noiat.elg|Cool pull - no IAT]] \\ +[[https://​www.ecmtuning.com/​images/​forums/​sddata/​coolwot-noiat.elg|Cool pull - no IAT]] \\ 
-[[http://​www.ecmtuning.com/​images/​forums/​sddata/​hotwot-noiat.elg|Hot pull - no IAT]]+[[https://​www.ecmtuning.com/​images/​forums/​sddata/​hotwot-noiat.elg|Hot pull - no IAT]]
  
 As before, these logs were taken minutes apart from each other on the same car.  The only difference between them is air temperature. ​ In the first, air temperature averaged 65F while in the second, it was 133F. As before, these logs were taken minutes apart from each other on the same car.  The only difference between them is air temperature. ​ In the first, air temperature averaged 65F while in the second, it was 133F.
  
 However, unlike the idle logs, measured A/F ratio in these actually *did* change, suggesting that air temperature in these log actually did have an impact on airflow entering the engine. However, unlike the idle logs, measured A/F ratio in these actually *did* change, suggesting that air temperature in these log actually did have an impact on airflow entering the engine.
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sd101.1245074955.txt.gz · Last modified: 2009/06/15 10:09 by dmertz